EFFECTS OF STAGE AND INTENSITY OF REPRODUCTIVE ORGANS PRUNING ON YIELD AND QUALITY OF PEPPER (Capsicum annuum L.) AT HUMBO, SOUTHERN ETHIOPIA

M. Sc. Thesis

ASHENAFI W/SELASSIE

January 2011 Haramaya University

ii

EFFECTS OF STAGE AND INTENSITY OF REPRODUCTIVE ORGANS PRUNING ON YIELD AND QUALITY OF PEPPER (Capsicum annuum L.) AT HUMBO, SOUTHERN ETHIOPIA

A Thesis Submitted to School of Plant Sciences School of Graduate Studies

HARAMAYA UNIVERSITY

In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN AGRICULTURE (HORTICULTURE)

By

Ashenafi W/Selassie

January 2011 Haramaya University

iii

SCHOOL OF GRADUATE STUDIES HARAMAYA UNIVERSITY

As Thesis research advisor, I hereby certify that I have read and evaluated this thesis prepared under my guidance, by Ashenafi W/Selassie, Entitled: Effects of Stage and Intensity of Reproductive Organs Pruning on Yield and Quality of Pepper (Capsicum annuum L.) at Humbo, Southern Ethiopia

I recommend that it be submitted as fulfilling the thesis requirement.

Tekalign Tsegaw (PhD) ___________________ _____________ Name of Major Advisor Signature Date

As members of the Board of Examiners of the M. Sc. Thesis Open Defense examination, we certify that we have read and evaluated the thesis prepared by Ashenafi W/Selassie, and examined the candidate. We recommend that the Thesis be accepted as fulfilling the Thesis requirement for the degree of Master of Science in Agriculture (Horticulture).

____________________ ___________________ ________________

Name of Chairman Signature Date

____________________ ___________________ _______________

Name of Internal Examiner Signature Date

___________________ ____________________ _______________

Name of External Examiner Signature Date

Final approval and acceptance of the thesis is contingent upon the submission of the final copy of the thesis to the Council of Graduate Studies (CGS) through the Departmental Graduate Committee (DGC) of the candidates major department.

iv

DEDICATION

I dedicate this thesis manuscript to my father Ato W/SELASSIE TESHALE, and my mother W/ro BIZUAYEHU BEKELE, for nursing me with affection and love and for their dedicated partnership in the success of my life.

v

STATEMENT OF THE AUTHOR

First, I declare that this thesis is my bonafide work and that all sources of materials used for this thesis have been duly acknowledged. This thesis has been submitted in partial fulfillment of the requirements for an advanced M.Sc. degree at the Haramaya University and is deposited at the University Library to be made available to borrowers under rules of the Library. I solemnly declare that this thesis is not submitted to any other institution anywhere for the award of any academic degree, diploma or certificate.

Brief quotations from this thesis are allowable without special permission provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the School of Graduate Studies where in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

Name: Ashenafi W/Selassie Teshale Signature: _______________

Place: Haramaya University, Haramaya

Date of submission: _____________________

vi

LIST OF ABBREVIATIONS

ANOVA Analysis of Variance CV Coefficient of Variation DAP Di Ammonium Phosphate DF Degree of Freedom DWIFP Dry Weight of Individual Fruit per Plant ECSA Ethiopia Central Statistical Authority EEPA Ethiopian Export Promotion Agency EYP Early Yield per Plant FD Fruit Diameter FL Fruit Length FV Fruit Volume FWIFP Fresh Weight of Individual Fruit per Plant m.a.s.l Meter above sea level MFNP Marketable Fruit Number per Plant MFYP Marketable Fruit Yield per Plant P Parameters PT Pericarp Thickness SDWF Seed Dry Weight per Fruit SNF Seeds Number per Fruit SNNPRS Southern Nation Nationalities and Peoples Regional State TDWP Total Dry Weight of the Plant TDWFP Total Dry Weight of Fruit per Plant TFYP Total Fruit Yield per Plant TFYPH Total Fruit Yield per Hectare TLA Total Leaf Area UMFNP Unmarketable Fruit Number per Plant UMFYP Unmarketable Fruit Yield per Plant VDWP Vegetative Dry Weight of the Plant

vii

BIOGRAPHICAL SKETCH

The author was born in Arsi Zone, Jeju Woreda, Addis Hiwot Kebele in May 08, 1985. He attended his Elementary School Education at Birra Elementary School, and he also attended his Secondary School Education at Kersa Secondary School (grade 9-grade 10) and at Asella Comprehensive Secondary School (grade 11-grade 12). He joined Haramaya University in 2004 and obtained the Bachelor of Science Degree in Agriculture (Plant Sciences) in 2006. He was employed by Wolaita Soddo Agricultural Technical Vocational Education and Training College in 2007. He served the college as an instructor in the Department of Plant Sciences. He joined the School of Graduate Studies of Haramaya University in 2008.

viii

ACKNOWLEDGMENTS

This study owes its existence to the help, support, and inspiration of many people. In the first place I would like to express my sincere appreciation and gratitude to my advisor Dr. Tekalign Tsegaw, for his close friendship, amicably motivating, scientifically supporting and genuinely criticizing me from the time the study was conceived right up to its completion. The genuine understanding of him as the author was a self sponsor student and multidirectional support made by him never been forgotten. I am extremely honored to be one of his students and I wish to boost the knowledge and confidence he has given me.

My special thanks go to Helen Teshome for her dedicated assistance, encouragement and ever ready help through the entire period of this work. The visit made by her to my research field at Humbo was highly appreciated and never to be forgotten.

I am highly indebted to Ato Meseret Meskele for his dedicated help in mobilizing and organizing all the necessary facilities that enabled me to accomplish this work successfully.

I also would like to extend my best appreciation to all academic staff members of Wolaita Soddo ATVET College, particularly Kassaw Bishaw, Solomon Yohannes, Hailu Gebru, Abera Habtaie, Abebe Fikadu, Milkias Asmamaw, Bisrat Hailemechael, Alemayehu Ayele, Abera Aanja, Alebachew Dejene, Messele Kassaw, Dereje Kassaye, Getnet Mekonnen, Mihiretu Shirko, Sintayehu Shibru, Belayhun Bezabihe, Addiszemen Aklilu, Amanuel Anjulo, Wondossen Mitiku, Selamawit Bekele, Melkamu Bezabihe, Gerawork Belaynehe, Muleken Kinfe, Biruk Molla, Messfin Assamenew and Shambel Bekele, for their valuable comments in the execution of the project.

Sincerely thanks are also due to all friends, especially Fanuel Leakemariam, Bizuayehu Desta, Degife Assefa, Getachew Kiffole, Mebratu Abera and Gizachew W/Senbet. who accord me technical and moral support during the study period. I also would like to express my heartfelt gratitude to my family members for their endless encouragement and financial support during the study period.

Above all, I would like to thank the Almighty God for He made all things possible to finish the study.

ix

TABLE OF CONTENTS

STATEMENT OF THE AUTHOR v LIST OF ABBREVIATIONS vi BIOGRAPHICAL SKETCH vii ACKNOWLEDGMENTS viii LIST OF TABLES xi LIST OF TABLES IN THE APPENDIX xii ABSTRACT xiii 1. INTRODUCTION 1 2. LITERATURE REVIEW 4

2.1. Taxonomy of Pepper 4 2.2. Origin and Geographical Distribution of Pepper 4 2.3. Botany of Pepper 5 2.4. Ecology of Pepper 6 2.5. Uses of Pepper 6 2.6. Flower and Fruit Physiology of Pepper 7

2.6.1. Flower and fruit abortion in pepper in relation to source and sink strength 7 2.6.2. Assimilate partitioning and sink strength 8

2.7. Effects of Fruit Pruning 10 2.7.1. Effect of fruit pruning on vegetative growth and Fruit size 10 2.7.2. Fruit pruning and assimilate production 11 2.7.3. Effect of fruit pruning on assimilate partitioning 12 2.7.4. Effect of fruit pruning on earliness of harvest period 13 2.7.5. Fruit pruning and physiological disorders 14

2.8. The use of plant growth regulators to regulate fruit number and size 15 3. MATERIALS AND METHODS 16

3.1. Description of the Study Site 16 3.2. Field Experiment 16

3.2.1. Planting material 16 3.2.2. Treatments and experimental design 16

3.3. Cultural Practices 17 3.4. Data Collected 18

3.4.1. Yield assessment 18 3.4.2. Fruit quality 20

3.5. Data Analysis 20 4. RESULTS AND DISCUSSION 21

x

TABLE OF CONTENTS (continued)

4.1 Yield and Yield Components 21 4.1.1. Fresh and dry weight of individual fruit per plant and seed dry weight per fruit 21 4.1.2. Total dry weight of fruit per plant 22 4.1.3. Total leaf area 23 4.1.4. Vegetative dry weight of the plant 23 4.1.5. Total dry weight of the plant 24 4.1.6. Seed number per fruit 25 4.1.7. Early yield per plant 26 4.1.8. Marketable and unmarketable fruit yield per plant 26 4.1.9. Marketable and unmarketable fruit number per plant 27 4.1.10. Total fruit yield per plant and per hectare 28

4.2 Fruit Quality 29 4.2.1. Fruit length 29 4.2.2. Fruit diameter 29 4.2.3 Fruit volume 30 4.2.4. Pericarp thickness of fruit 30

5. SUMMARY AND CONCLUSIONS 32 6.REFERENCES 35 7. APPENDICES 43

xi

LIST OF TABLES

Table Page 1. Fresh and dry weight of individual fruit per plant, seed dry weight per

fruit, total dry weight of fruit per plant and early yield per plant of pepper as affected by stage and intensity of reproductive organs pruning ....................................... 22

2. The interaction effect of stage and intensity of reproductive organs pruning on seed number per fruit, vegetative and total dry weight of the plant and total leaf area of pepper ......................................................................................... 25

3. Marketable and unmarketable fruit yield per plant, and number of marketable and unmarketable fruit per plant as affected by stage and intensity of reproductive organs pruning .............................................................................. 28

4. The interaction effect of stage and intensity of reproductive organs pruning on fruit length, fruit diameter, fruit volume and pericarp thickness of pepper fruit ....................................................................................................................... 30

xii

LIST OF TABLES IN THE APPENDIX

AppendixTable Page 1. Correlation coefficient of the parameters measured ............................................................. 44 2. The ANOVA output of all parameters in respect to mean sum of square

and coefficient of variation ................................................................................................... 46

xiii

EFFECTS OF STAGE AND INTENSITY OF REPRODUCTIVE ORGANS PRUNING ON YIELD AND QUALITY OF PEPPER (Capsicum annuum L.)

AT HUMBO, SOUTHERN ETHIOPIA

ABSTRACT

The continuous growth of pepper plant in tropics increase the number of fruits per plant and this in turn increases the potential for competition between fruits with consequent reduction in fruit size. Field experiment was conducted on farmers field from November 2009 to June 2010 at Humbo, Southern Ethiopia, to assess the effects of stage and intensity of reproductive organs pruning on yield and quality of pepper. Four levels of pruning (control, one-reproductive organ, two-reproductive organs and three-reproductive organs) and three stages of pruning (bud, anthesis and fruit set), were arranged in factorial combination in Randomized Complete Block Design with three replications. Pepper cultivar called Marekofana was used. The interaction effect of three- reproductive organs pruned treatment with fruit set stage gave the highest for total leaf area (6945.88 cm2) of pepper and the least was obtained from the control. Three- reproductive organs pruning improved fresh and dry weight of individual fruits per plant and seed dry weight per fruit by about 109.64%, 52.8% and 65%, respectively. The highest total dry weight of fruit per plant (54.11 g) was from the control plants and the least (38.72 g) being at three- reproductive organs pruning. The highest vegetative dry weight (71.87 g) of the plant and total dry weight of the plant (110.59 g) were obtained three- reproductive organs were pruned at anthesis stage and the lowest (56.9 g) and (102.18 g) were obtained from the control respectively. The highest (148.21) and the lowest (100.15) seed number per fruit recorded two- reproductive organs were pruned at bud stage and from the control treatment, respectively. The highest early yield per plant (110 g) was obtained from the control and significant reduction was observed with reproductive organs pruning. The highest (170.63 g) and the lowest (151.3 g) marketable fruit yield per plant were obtained from one- reproductive organ and the three- reproductive organs pruned treatment, respectively. On the contrary, the highest (8.24 g) and the lowest (4.49 g) unmarketable fruit yield per plant were obtained from the three- reproductive organs and one- reproductive organ pruned treatment, respectively. The highest marketable (36.44) and unmarketable (3.76) fruit number per plant were obtained from the control while the lowest marketable (16.4) and unmarketable (1.04) fruit number per plant were obtained from the three- reproductive organs pruned treatment. The highest total fruit yield per plant (174.94 g) and total fruit yield per hectare (8334.4 kg) were obtained from one- reproductive organ pruned treatment and the lowest total fruit yield per plant (159.54 g) and per hectare (7543.20 kg) were obtained from the three- reproductive organs pruned treatment The interaction effect of three- reproductive organs pruned treatment with fruit set stage gave the highest fruit length (14.64 cm), pericarp thickness(3.65 mm) and fruit diameter(2.98 cm) and the least values were obtained from the control. The interaction effect of three- reproductive organs pruned treatment with anthesis stage gave the highest fruit volume (33.98 cm3) and the least values were obtained from the control. From the result of this study, intensity of pruning had a better effect than stage of pruning in evaluation of source-sink relationships of pepper. Therefore, it can be concluded that one- reproductive organ pruned treatment gave better yield and quality without affecting total and marketable fruit yield per plant. While the combination of three- reproductive organs pruned at fruit set stage and anthesis stage gave the better qualities of pepper fruit at the expense of yield loss, but to reach at a conclusive result and recommendation, further study should be done across location and season.

xiv

1

1. INTRODUCTION

Pepper (Capsicum annuum L.) is an important horticultural crop belonging to the family Solanaceae. Capsicum genus includes many species of which the major ones are Capsicum frutescens L. and Capsicum annuum L. (Osman, 2003). According to FAO (2007) report, world production of pepper was 28.4 million tons in both dry and green fruits from 3.3 million hectare of land, with annual growth rate of 0.5 percent. Correspondingly, ECSA (2009/2010) reported that peasants produced 61,463.7 tons of green pepper and 159,327.5 tons of red pepper on 7,850 ha and 89,866 ha of land, respectively with average productivity of 78.3 qt ha-1 of green pepper and 17.73 qt ha-1 of red pepper. Even though there is no written information, pepper was believed to be introduced to Ethiopia probably by the Portuguese in the 17 century (Hafnagel, 1961). The author also reported that Ethiopia is one of a few developing countries that have been producing paprika and capsicum oleoresins for the export markets.

Pepper is an economically and traditionally important crop in Ethiopia. ). It is a major spice and vegetable crop produced by the majority of farmers in SNNPRS, Oromia, and Amhara regions (EEPA, 2003). In addition to its export value, the powder from the dried pod is the main component in the daily diet of Ethiopians. Woredas such as Awassa, Alaba, Ziway, Mareko, Boditti, Humbo, Meki, and Koka in the rift valley parts are the major producing areas of the crop. In these areas, pepper serves additionally as income generating crops for on-farm activities of farmers particularly in the time of cereal deficit (Tameru et al., 2003). Humbo is one of the Wolaita woreda where pepper is highly grown and it uses for income generation and for the preparation of traditional sauce called Datta which is a popular sauce mainly eaten with meat and other foods.

Pepper is warm season crop which is annual in temperate regions, but can produce continuous growth in tropical areas. The continuous growth of the plant in tropics increase the number of

fruit per plants and which increases the potential for competition between fruits and the consequent reduction in fruit size (Van Ravestijin and molhoek, 1978). Different cultural methods can be used to manipulate fruit size, pericarp thickness and freedom from defects and

most of these methods, however, entail chemicals that may not be acceptable to the consumer.

2

A non-chemical method is by pruning some of the flowers of young fruits. However, removing potential fruit will influence the sink in the sink: source interaction and the partitioning of assimilate. Furthermore, if pruning is not done at the appropriate level and time, fruit disorder, yield loss and inhibition of dry matter production may occur (Tsedal, 2004). Therefore, research activities are needed to establish the optimum level of pruning and stage of pruning to increase yield and quality of pepper. Pruning of some of the flowers or fruits from crops like tomato and pepper results in assimilate re-distribution to the remaining fruits and increase their size. However, the extent of re-distribution of assimilates to the remaining fruits appears to depend

mainly on the sink-strength of fruit which varies with age of fruit and on the transport path way (Kinet and Peet, 1997). Since fruits utilize the major portions of the photo assimilates in crops like tomatoes and peppers, variation in fruit number will influence their size (Gautier et al., 2001). It is possible to maintain fruit size with in a preferred size range by altering fruit number. This can be achieved by fruit pruning, thus increasing the supply of assimilates to the remaining fruit (Cockshull and Ho, 1995). If too many fruits are pruned from the plant, those remaining may be more prone to growth disorders such as cracking, blossom end-rot and fruit deformation (Aloni et al., 1996).

Redistribution of assimilates to the remaining fruit may not be completely compensated for the

loss of fruit if pruning is done in excess, or too late, for instance; if the fruit is subjected to pruning after it has already accumulated a large quantity of assimilates. The degree to which

plants can compensate for reduced fruit numbers by increased fruit size depends on factors like the cultivar, seed number, and fruit position (Tsedal, 2004). To avoid yield losses the degree of thinning must be adjusted to obtain a desirable fruit size in the remaining fruit (Cockshull and Ho, 1995).

It has been reported that time and intensity of pruning significantly influenced dry matter production as well as sink:source interaction and ultimately fruit yield and quality. Moreover, identification of the optimum time and intensity of pruning is critically important for

commercially cultivated tomato varieties to avoid under and over truss pruning which is known to influence the productivity of tomato (Terry and Boyhan, 2006). A lot of researches have been conducted and much information is available on the source-sink relationships of

3

tomato, on the contrary, little information existed in pepper (Tsedal, 2004). The available previous works in source-sink relationships of pepper were carried out in the greenhouse conditions (under controlled environment). No works have been studied in source-sink relationships of pepper as a means to improve quality and maximizing productivity in Ethiopia in general and at Humbo area specifically. Therefore, studies on a non chemical method of reproductive organs pruning had significantly importance as the pepper cultivar Marekofana is widely grown in the different parts of the country as fresh market and dried pods. Ethiopians have strong attachments to dark red pepper, which has high value principally for its high

pungency. The fine powdered pungent product is an indispensable flavoring and coloring ingredient in the common traditional sauce wot where as the green pod is consumed as

vegetable with other food items. There is a general belief among Ethiopians that a person who frequently consumes hot pepper has resistance to various diseses. Besides, it has significant economic importance in the country, vital role as a means of income generation to the farmers

and immense potential in the country for expansion and for export markets. Hence, there is no recommendation when and at what intensity reproductive organs pruning should be effected to regulate fruit size and ultimately to influence fruit yield and quality. Therefore, this study was initiated with the objective of assessing the effect of stage and intensity of reproductive organs pruning on yield and quality of pepper.

4

2. LITERATURE REVIEW

2.1. Taxonomy of Pepper

The genus Capsicum perhaps comes from the Latin word capsa, meaning chest or box because of the shape of fruits, which enclose seeds very neatly, as in a box. The Capsicum (2n=24) encompasses a diverse group of plants producing pungent or non-pungent fruits. At present, it is widely accepted that the genus consists of approximately 25 wild and five cultivated species. Based on the genus flow through natural and conventional hybridization,

the capsicum species are grouped in five species complexes. Among the cultivated species,Viz, Capsicum annuum, Capsicum frutescens, Capsicum chinense, Capsicum baccatum and Capsicum pubescens, the cultivation of Capsicum annuum is the most widely spread all over the world (Berke et al., 2005). All the five cultivated species of capsicum are represented by genotypes with pungent (hot pepper) and non-pungent (sweet pepper) fruits. Furthermore, these species have huge variability for fruit size/shape and pungency and often genotypes with similar fruit morphology exists across the species. Hence, assigning a given genotype to a

specific cultivated species based on fruit size, shape and pungency is difficult. Nevertheless,

certain flower and fruit descriptors may be used to assign a genotype to a cultivated species without much doubt (Govindarajan and Sathyanarayana, 1991).

2.2. Origin and Geographical Distribution of Pepper

Pepper (Capsicum annum L.) was domesticated in the highlands of Mexico and includes most of the Mexican Chile (syn.chilli) of Asia and Africa and sweet pepper of temperate countries. However, due to the non- adaptability of Capsicum annuum in lowland tropic of Latin

America, its cultivation was replaced by Capsicum frutescens and Capsicum chinense. The cultivation of Capsicum baccatum and Capsicum pubescens is mostly restricted to Latin

America countries like Peru, Bolivia, Columbia and Brazil. In India, although Capsicum annuum is most widely cultivated, Capsicum frutescens, Capsicum chinense and Capsicum baccatum are also known in specific regions. Except for Capsicum pubescens, wild forms of the remaining four cultivated species are known (Govindarajan and Sathyanarayana, 1991).

5

2.3. Botany of Pepper

Pepper (Capsicum annuum L.) is a very variable herb, or sub-shrub, sometimes woody at the base, erect, much branched, 0.5-1.5 m high; grown as an annual; peppers are erect or sometimes prostrate in growth habit (Purseglove, 2000). Root structure develops from a strong tap root that succumbs to laterally branched fibrous roots; vegetative growth patterns can be discerned form a dichotomous branching of the main stem and lateral shoots. Alternately appearing leaves are simple, petiole, and ovate, sometimes lanceolate, and have entire leaf

margins; on the main stem, leaves are arranged spirally. Perfect flowers and fruits are usually borne singly at each terminal node. Pedicels may be erect or pendant. Calyx shape is

campanulate with smooth to dentate margins. The peduncle and calyx are normally attached to mature fruit (Bosland and Votava, 2000).

There is no abscission layer at the attachment of the peduncle to the calyx, flowers are white,

with five to seven lobes per corolla and five to seven stamens with blue anthers. Corolla diameter ranges from 8-15mm. Fruits are multi seeded berries with crisp flesh and a central cavity partitioned into two or more locules (Messiaen, 1992).

Capsicum annuum is an autogamous or self-pollinating species; however, a considerable amount of cross-pollination occurs mainly through insects and to lesser extent through wind (Bosland and Votava, 2000). Among pepper cultivars, there is noticeable heterosty where flowers differ in the position of their stigma in relation to the anthers. The long-styled flower in

which the stigma extends beyond the stamens favor cross-pollination where as a high degree of self-pollination is expected from the short-styled flowers; protogyny, that phase when the

stigma is receptive before pollen shedding, is common also in some varieties (Simonne et al., 1998).

Capsicum annuum can be divided between sweet and hot peppers. The sweet pepper also known as bell pepper and is relatively non pungent, has thick flesh and the hot or spicy peppers are pungent due to the volatile phenol compounds known as capsaicin (C12H27NO3) (Bosland and Votava, 2000). This may vary between 0.2 - 4 % in different cultivars (Jansen,

6

1981). The pungent (hot) principles of these spices is capsaicin which is present at about 0.2% abundance in the mild types of Capsicum and up to about 1 % in the most pungent types of chilies; Paprika (a ground product valued principally for coloring power, bell or green peppers (fresh vegetable pepper) (Jackson et al., 1985).

2.4. Ecology of Pepper

Pepper (Capsicum annuum L.) is a dicotyledonous woody perennial small shrub in suitable climatic condition, living for a decade or more in the tropics. It has erect growth habit

sometimes prostate growth habit that may vary in certain characteristics depending on types of species. Pepper (Capsicum annuum L.) is a tropical species, but adapted to cultivation of temperate regions during summer, or in protected cultivation, or year round. Pepper is quite adapted to hot weather. Optimum temperature for growth and production are between 18 oC and 30 oC. Seed germinate well at 25-30 oC. When temperature falls below 15 oC or exceeds 32 oC, growth is usually retarded, blossoms drop, and fruit set is prevented (Knott and Deanon, 1967). Pollen viability is significantly reduced at temperatures above 30 oC and below 15 oC. Cool night down to 15 oC favors fruit setting. Capsicum is day-neutral, but certain forms show photoperiodic reactions; long day may slightly delay the first flowering. It tolerates shade up to 45% of solar radiation. The crop is grown at wide range of altitudes from low land up to 2000 m.a.s.l. In Ethiopia even up to 3000 m.a.s.l where extremely rain fed condition, and High yields are obtained with a rain fall of 600 mm up to 1250 mm that are well distributed over the growing season (Smith et al., 1998). Pepper (Capsicum annuum L.) grows on almost all soil types, but is most suited to well drain sandy or loamy soils, rich in lime, with a pH of 5.5-6.8 and high water retention capacity. Severe flooding or drought is injurious. Water logging causes poor fruit setting, diseases and fruit rotting. Capsicum is moderately sensitive to soil salinity (Berke et al., 2005).

2.5. Uses of Pepper

Pepper (Capsicum annuum L.) is an important agricultural crop, not only because of its economic importance, but also due to nutritional and medicinal value of its fruits (Qumer,

7

2009). It is an excellent source of natural colors and antioxidant compounds (Howard et al., 2000). A wide spectrum of antioxidant vitamins, carotenoids, capsaicinoids and phenolic compounds are present in pepper fruits. The intake of these compounds in food is an important health-protecting factor by prevention of widespread human diseases. As consumption continues to increase, hot peppers could provide important amounts of nutritional antioxidants to the human diet. Level of these antioxidants can vary with genotype, stage of at harvest, storage and processing conditions (Daood et al., 1996; Marin et al., 2004).

The Capsicum fruits are an excellent source of natural micronutrients (vitamins C, E and carotenoids) which appear to be critically important in preventing or reducing chronic and age-related diseases. Fruits from the pungent hot type pepper plant are historically employed in traditional medicine and are currently being used in modern herbology and conventional medicines. Capsaicin, the predominant compound in pungent types of Capsicum, induces depletion of substance Phosphorous and other neuropeptides from sensory nerve terminals. A capsaicin cream has been introduced into dermatologic therapy and proven useful in preventing chronic pain associated with post-herpetic neuralgia, diabetic neuropathy, and other pain syndromes (Palevitch and Craker, 1996).

2.6. Flower and Fruit Physiology of Pepper

2.6.1. Flower and fruit abortion in pepper in relation to source and sink strength

Abscission of flower buds, flowers, and fruits is an important yield-limiting factor in many

crops including pepper (Wien et al., 1989a). However, the simulation of organ abortion is one of the weak features of crop growth models, despite the strong influence on partitioning and yield (Marcelis et al., 1998).

Environmental stresses such as heat, drought, and low light conditions or failure of pollination/fertilization are important factors that may induce abscission (Wien et al., 1989a; Aloni et al., 1996; Marcelis and Baan Hofman-Eijer, 1997). Pepper, like some other fruit vegetables, shows a cyclic growth pattern where periods of high fruit set and slow fruit growth

alternate with periods of low fruit set and rapid fruit growth (Kato and Tanaka, 1971; Marcelis, 1992).

8

Several studies suggested that fruit set is related to the assimilate supply (source strength). For example, shading decreased fruit set in many crops (Guinn, 1974; Kinet, 1977; Wien et al., 1989b, Aloni et al., 1996). Differences in susceptibility to abortion of pepper cultivars have been related to assimilate production of the plant and partitioning into reproductive organs (Turner and Wien, 1994).

2.6.2. Assimilate partitioning and sink strength

The actively growing pepper fruit is believed to be a stronger sink than a flower or maturing fruit (Ali and Kelly, 1992). However, the studies done by Marcelis and Baan Hofman-Eijer (1995) on growth analysis studies showed that the sink-strength of pepper fruit was hard to determine. This was due to the occurrence of fruit deformation and blossom-end rot when fruits were grown under non-limiting assimilate supply.

Competitive limitations on the growth rates of fruit begin as increasing numbers of fruit mobilize nutrient supplies for their growth. Since the pattern of such mobilization is mainly determined by the sink strength (Schapendonk and Brouwer, 1984), which in turn is determined by the age (developmental stage) of the sink, earlier formed fruit inhibit the growth of younger fruit and flowers in many plant species. Ali and Kelly (1992) demonstrated the limitations exerted by older fruit at the upper fruiting nodes on younger fruit of the third and fourth nodes, and the negative consequences on their size in sweet pepper plants. At the time when the lower fruit were actively mobilizing assimilates and nutrients for their growth, those on the upper nodes were at a less competitive flower bud stage.

As fruits are important sinks for assimilates, the effect of earlier formed fruits are probably not only mediated through assimilate availability, but also hormonal control (Ruiz and Guardiola, 1994) or a combination of these factors (Schapendonk and Brouwer, 1984). Generally, a clear distinction between dominance and competition for a limited assimilate supply is difficult to

make. Frequently, dominance can be observed very early in the ontogeny of fruit/sinks where in many cases competition for assimilates is less likely, because of the low demand of small sinks

for assimilates (Bohner and Bangerth, 1988). In some instances, elimination of the dominating Organs during these early stage lead to a yield over- compensation of the remaining sinks

9

(Ojehomon, 1970), indicating that assimilate availability was not limiting. Therefore, dominance was most likely the reason for the depressed growth of these organs. Dominance of the first formed fruit may be exercised in several ways, which include a pressure gradient, sink development sequence, growth inhibitors and seed number.

Earlier formed fruit may constitute a stronger sink for assimilates, due to a higher pressure-gradient between sink and source (Bangerth and Ho, 1984). This gradient may be in part mediated by the action of growth hormones such as auxins and cytokinins activity in the

growing fruit. However, levels of extractable auxins in the fruit have not correlated well with relative fruit growth (Ho et al., 1982; Bohner and Bangerth, 1988).

A hypothesis reviewed by Bangerth (1989) stated that the sequence of sink development might establish the dominance effect. Results in the same study show that the polar Indole Acetic Acid (IAA) export of the earlier developed sink inhibits the IAA export of later developed sinks. This inhibition occurs at the junctions where Auxin streams from various sinks meet. It is suggested that this depressed IAA export of the subordinated fruit/sink acts as the signal that leads to inhibited development.

Another possible way in which dominance could be maintained by tomato fruit may be through the production of a growth inhibitor such as Abscisic Acid (ABA) (Tsedal, 2004). Abscisic Acid content of competing tomato fruit has, however, not shown any relationship with fruit growth

inhibition (Ho et al., 1982; Bohner and Bangerth, 1988).

In many species, including peppers and tomatoes, fruit size has been reported to be positively correlated with seed number (Stephenson et al., 1988). Apart from stimulating growth of a fruit, the seed number was also found to increase the inhibitory effect of the fruit on growth of later developing fruit. Fruit with low and medium seed numbers seem to be far less capable of

inhibiting younger fruit with high seed numbers than vise versa. Thus, it was concluded that differences in seed number among developing fruit could override the dominance of the first fruit. Stephenson et al. (1988) predicted that reductions in seed number would reduce the dominance of the first fruit. Consequently, first-fruit dominance is nearly absent from

10

Parthenocarpic plants; whereas seeded lines of the same species exhibit strong first-fruit dominance (Cantliffe, 1974).

Seeds are well known to be rich sources of plant growth regulators (Hedden and Hoad, 1985). Sjut and Bangerth (1984) reported that auxin production and export by a fruit is predominantly confined to the seeds. As the result of this auxin export, seeds of a fruit may affect competition between fruit, either by increasing the sink strength (competitive ability to attract assimilates) of the fruit, or by suppressing the sink strength of other fruit (Bangerth, 1989). In a study by Zhiyuang et al. (1982) removal of the two earliest flowers of capsicum plants increased the seed content of the remaining fruit.

2.7. Effects of Fruit Pruning

2.7.1. Effect of fruit pruning on vegetative growth and Fruit size

Vegetative growth of fruit-bearing plants appears to be regulated by the developing fruit (Gautier et al., 2001). As fruit are the major sink of the plant, a reduction in fruit load could favor the distribution of dry mass to the vegetative parts of the plant (stem, leaves and root). Heuvelink and Buiskool (1995) observed that changes in dry matter distribution under high fruit load were correlated with lower leaf areas. Their data suggested that leaves and fruit compete for assimilates. For this reason, it is common practice to remove the flower buds from the first and second layers, so that fruit development does not check the plants before they build up sufficient foliage to support maximum yields, and fruit will then grow to the optimum size. Excessive fruit loads can also stress the plant in other ways. The root system may degenerate, allowing attack by pathogens. Thus, it is recommended that growers control fruit load in young plants. This process also allows for the removal of any misshapen fruit that have formed (Morgan and Lennard, 2000). Gautier et al. (2001) found an increase in mean dry weight of stems and petioles (up to 43%), and lamina (up to 22%) along with an increase in mean dry weight of fruit (up to 42%), when tomato flowers were pruned. Thus, maintaining an optimum balance between partitioning to the harvestable organs (fruit) and the other plant parts (vegetative parts) is recommended (Marcelis and Heuvelink, 1999).

A number of studies show that the influence of pruning on fruit size. Saglam et al. (1999)

11

conducted a study to determine the effect of the number of fruit per truss (four, six or eight) on quality of tomatoes. Average fruit size was increased by decreasing the number of fruit per truss. Likewise, in a field trial of tomato, growth limited to six inflorescences and removal of 10% of the flowers from the trusses produced the best quality in terms of fruit size (Ramirez et al., 1977).

2.7.2. Fruit pruning and assimilate production

Apart from inducing fruit disorders, intensive pruning of reproductive sinks have been found to influence the production of assimilates. Hall and Milthorpe (1978) showed that removal of rapidly growing pepper fruit caused a 30% reduction in net CO2 uptake. Bhatt and Rao (1989) found a higher net photosynthetic rate in fruiting than de-blossomed bell pepper plants. Associated with this phenomena is the hypothesis that the concentration of assimilates in leaves

alters the net photosynthetic rates of those leaves (Ho, 1976) and referred to as end-product- inhibition.

The inhibition of leaf photosynthetic rate after sink removal may have several causes. (Gifford and Evans, 1981) explained the negative feedback control on photosynthesis by means of a hormonal mechanism influencing stomatal or mesophyl resistance. Similarly, stomatal closure

resulting from a build-up of abscisic acid in the leaf blade of peppers was found by Kriedemann et al. (1976). In some species, fruit removal results in an accumulation of starch grains in the leaves, which may interfere with the radiant energy reception in the chloroplasts (Schaffer et al., 1986). In others, accumulation of starch in the plastids may distort the membrane structure of the chloroplast enough to lower gas exchange rates (Goldschmidt and Huber, 1992). In a study by Tanaka and Fujita (1974), removing one out of three trusses from a tomato plant had no influence on dry matter production. Removal of all trusses, however, reduced final dry weight by 40%. The authors also observed that pruning three out of six fruit per truss reduced dry matter production by 20%. To the contrary, Bhatt and Rao (1997) found a higher net photosynthetic rate in two sweet pepper cultivars where reproductive sinks were pruned than in

control plants. The result of this study indicated that the developing fruit on lower nodes are the dominant sink in bell pepper and the removal of these fruit resulted in faster growth of other fruit on upper nodes.

12

Heuvelink and Buiskool (1995) stated that the reduction in dry matter production for plants with low sink: source ratios does not necessarily reflect a reduction in leaf photosynthetic rate. Growth reductions resulted, at least partly, from reduced light interception. Plants with only one fruit per truss showed strongly curled leaves, which pointed downwards, instead of being almost horizontal. Leaf curling at low sink: source ratio was observed by Nederhoff et al. (1992). Light interception by these plants was decreased further as the plants were shorter, whereas neighboring plants (with no fruit or truss pruning) were of normal height.

Reduced leaf photosynthetic rate may be compensated for by a higher leaf area index, as fruit pruning favors assimilate distribution towards the vegetative plant parts, including the leaves

(Marcelis, 1991).

2.7.3. Effect of fruit pruning on assimilate partitioning

Cockshull and Ho (1995) found that removal of distal tomato fruits increased the size of proximal fruits. However, the redistribution of assimilates within the truss did not completely compensate for the loss of weight by removal of distal fruits, and there was redistribution of assimilates between trusses. Slack and Calvert (1977) also found that removing a truss resulted in an increased yield on some of the remaining trusses and the largest increase occurred on the trusses adjacent to the one that was removed. The effect was primarily through increased mean fruit size. Since fruit are the strongest sink for assimilates in tomatoes and peppers, a change in fruit number is mainly compensated by a corresponding inverse change in mean fruit size rather than by a substantial change in fruit: shoot ratio (Cockshull and Ho, 1995).

A study conducted by Bhatt and Rao ( 1997) indicated that removal of the fruit in the first flowering node of bell pepper plants ten days after fruit set did not increase the partitioning of dry mass to fruit on upper nodes of the plant. With the advancement of fruit growth, the first flowering node fruit acts as a major sink for photosynthates (10.2%) up to 20 days after flowering, and afterwards becomes a weaker sink (Bhatt and Rao, 1993). Ali and Kelly (1992) found that the inhibitory effect of old fruit on the increase in fresh weight, length, diameter and

pericarp thickness of younger ones was significant only from flower bud inception through weeks two and four after fruit set. In line with this, Bertin et al. (2002) concluded that cell

13

division is a main limiting factor for fruit growth under low assimilates supply, although cell enlargement during further fruit development is also affected.

In addition to sink-strength, relative distance of sources and sinks is assumed to affect assimilate partitioning. Slack and Calvert (1977) investigated the effect of removing individual trusses on yield of glasshouse-grown tomatoes. It was found that removing a truss resulted in yield increases on some of the remaining trusses both above and below the one removed. The largest increases occurred on the trusses immediately above and below the one removed and

there was a general tendency for the increases to be smaller the further away (in both directions) the truss was from the removed truss. Heuvelink and Buiskool (1995) argued that the results of Slack and Calvert (1977) could also be explained without assuming a distance effect on assimilate partitioning. Trusses closest to the excised truss show the highest yield increase as earlier initiated trusses have a shorter growth period left to profit from removing a truss, while later-initiated trusses miss a larger part of the period where removal of the truss plays a role.

It was concluded that the effect of distance (transport resistance) and the compartmentation of the plant into source-sink units could be omitted when modeling dry matter distribution and one common assimilate pool available to all sinks can be assumed. Andriolo et al. (2000) conducted a similar trial with tomato, and comparisons of fruit dry mass indicated that fruit position did not affect dry matter distribution, supporting the hypothesis of one common pool of assimilates

circulating freely in the plant. In contrast to this, Marcelis (1996) reasoned that some of these results could be explained by the fact that sometimes sinks were functioning close to assimilate saturation (sink limitation). The model on phloem transport proposed by Minchin et al. (1993) accepts that transport resistance does not affect partitioning when sinks are functioning at saturation. Hence, the role of distance on translocation is still controversial.

2.7.4. Effect of fruit pruning on earliness of harvest period

From the growers' point of view, fruit quality and earliness of production are as important as

14

the quantity of fruit production (Schapendonk and Brouwer, 1984). In indeterminate flowering plants, an uncontrolled increase of the demand for assimilates leads to a surplus of slowly growing fruit. This is supposed to be overcome by manipulation of the number of fruit that are growing simultaneously. Bhatt and Rao (1997) found that the removal of fruit on lower nodes of bell pepper, which were major reproductive sinks for photosynthesis, resulted in faster growth of fruit on upper nodes. In contrast to this, Saglam et al. (1999) found that earliness was not significantly influenced by the number of fruit per plant in tomato. Neither did they observe a shorter harvesting period by decreasing the number of fruit per truss. In most cases, organ

size is directly related with ontogeny, and therefore, it is difficult to discriminate between effects of organ size and ontogeny (Tsedal, 2004).

2.7.5. Fruit pruning and physiological disorders

Blossom-end rot is the most serious physiological disorder (Kaloo, 1986). The first symptom is a small, water-soaked spot at or near the blossom scar of green tomatoes. As the spot enlarges the affected tissue dries out and becomes light brown to dark brown. Then the lesion develops in to a well-defined sunken spot with the affected tissues collapsed and leathery (Atherton and Rudich, 1986). The immediate cause of blossom-end rot is a deficiency of calcium at the growing point (blossom-end) of locular tissue. The number of vascular bundles decreases from the weeks after anthesis, rapid expansion of the fruit takes place thus reducing the density of bundles dramatically. As a result, deposition of calcium in the distal pulp tissue decreases and the calcium requirements of cell walls and cell membranes may not be met. De Kreij (1992) reasoned that excessive vegetative growth and low fruit load (severe pruning) is said to favor a disequilibrium between xylem and phloem sap absorption by the fruit, in favor of the phloem

sap, and lead to calcium deficiency in the fruit and increase the appearance of blossom-end rot. In peppers, small, deformed and Parthenocarpic fruit develop after severe fruit/flower pruning (Aloni et al., 1991). Such fruit develop from flowers with enlarged ovaries in which self-pollination is inefficient due to the large distance between the stigma and stamen. Aloni et al. (1999) suggested that assimilates which are normally transported to developing fruit may be transported, upon fruit removal, to the flower buds. According to Aloni et al. (1999) the sensitivity of the flower to carbon supply depends on its stage of development. Depending on the extent, fruit cracking reduces fruit appeal (Peet and Willits, 1995), reduces fruit shelf-life

15

(Hayman, 1987), increases fruit susceptibility to pathogens (Peet and Willits, 1995) and reduces fruit marketability (Peet, 1992). Generally, fruit cracking is associated with the rapid movement of water and sugars towards the fruit when cuticle elasticity and resistance are weak during ripening (Dorais and Papadopoulos, 2001). High foliage: fruit ratio resulting from fruit pruning significantly increases the number of fruit affected by cracking (Ehret et al., 1993). Similarly, pruning of tomato plants to three trusses resulted in the highest percentage of cracked fruit as compared to plants pruned to five or seven trusses. Moreover, Oliveira et al. (1996) observed that while a reduction in the number of fruit per plant increased their size, it also increased the

number of fruit affected by cracking.

2.8. The Use of Plant Growth Regulators to Regulate Fruit Number and Size

Plant growth regulators (PGR) are used extensively in horticulture to enhance plant growth and improve yield by increasing fruit number, fruit set and size. Improvement in vegetative growth and yield attributes may enhance crop productivity. Productivity in horticultural system is often

depend on manipulation of physiological activities of the crop by chemical means (Yeshitela et al., 2004) and this is modulated by the interaction of the PGR with plant development processes. According to Gianfagna (1978), plant growth regulators can modify development by interfering with biosynthesis, metabolism or translocation of endogenous hormones, or may supplement endogenous hormones when their levels are reduced. Developmental process reported to be influenced by plant growth regulators application include, induced flowering in Arabidopsis thaliana by gibberellins (Richard et al., 2001), increased fruit fresh weight in cucumber by Benzyladenin (BA) plus Gebberellins (GA4+7) (Batlang et al., 2006). In the study conducted by Batlang (2008) in green house grown hot pepper, accel (BA plus GA4+7) treatment increased fruit yield but did not significantly affect number of fruits, number of branches and plant height. The increase in yield due to accel treatment was associated with significance increase in fruit fresh weight and length. Therefore, they concluded that the increase in yield was due to increase in fruit size and suggested that accel application has the

potential to be used as a management practice in green house production of hot pepper.

16

3. MATERIALS AND METHODS

3.1. Description of the Study Site

The study was conducted on farmer field at Humbo woreda of Wolaita Zone in 2009/2010 belg growing season. Humbo is located in the Southern Nation Nationalities and Peoples Regional State. It is located at 6o4046"N latitude and 37o4656"E longitude at an altitude of 1450 m.a.s.l and 408 km south of Addis Ababa.

The area has bimodal rainfall distribution with mean annual rainfall of 500 mm. Seventy percent of the woreda has hot to warm climate with mean minimum and maximum air temperature of 24oC and 32oC, respectively. The soil is Nitisol, reddish brown in color and classified as sandy loam in texture (Gebre, 2007).

3.2. Field Experiment

3.2.1. Planting material

Pepper (Capsicum annuum L.) cultivar Mareko Fana was used for the study. As Peppers show a lot of variability, two main branches were retained per plant and the other ones were pruned just above its first leaf. In this way, plants with two main branches were formed.

3.2.2. Treatments and experimental design

The experiment was laid in a Randomized Complete Block Design (RCBD) in a 4x3 factorial arrangement with three replications. There were a total of twelve treatment combinations; four pruning intensities and three stages of pruning. The gross area of each plot was 10.5 m2, with 3 m length and 3.5 m width. The spacing between plots and adjacent replication were 1 m and 1.5 m, respectively. There was a total of 634.5 m2 area for experimental site.

17

Pruning intensities

Treatment 1: no reproductive organs pruned (control) Treatment 2: the first reproductive organ pruned Treatment 3: the first two reproductive organs pruned Treatment 4: the first three reproductive organs pruned

Stage of pruning

At bud stage

At anthesis of the first flower

At fruit set (when the first fruit was attained 2 mm in diameter).

3.3. Cultural Practices

Land preparation for nursery bed and main field were done in October 2009 and December 2009, respectively, using oxen and human labor. Seedlings of pepper were sown on November 1, 2009 on well prepared seed beds of 1 m width and 5 m length at spacing of 15 cm between rows. After sowing, the beds were covered with hay mulch until emergence. In the nursery 10

kg P2O5 ha-1 in the form of DAP (46% P2O5 and 18% N) at sowing and 10 kg N ha-1 in the form of urea (46% N) was applied after thinning. Well established seedlings (standard seedlings) at 3 to 4 leaves stage, were transplanted in January 29, 2010 to experimental field on ridges in five rows per plot at spacing of 70 x30 cm with 10 seedlings per row to obtain 50 plants per plot. The recommended fertilizer, 100 kg DAP ha-1 was applied once at transplanting and 100 kg urea ha-1 was applied 50% at transplanting and the remaining 50% at the onset of flowering. The fertilizers applied during transplanting were applied in a band form on the ridges and incorporated in the soil to facilitate nutrient up take by the plants. The crop was cultivated under supplementary irrigation conditions. No major disease and pest incidences were encountered, but weeding and other necessary cultural practices were employed uniformly to

all treatments during all the stages of crop growth.

18

3.4. Data Collected

Data on yield and quality components were taken from five randomly selected plants in the three central rows. Fruits were harvested at the mature red stage.

3.4.1. Yield assessment

Fresh weight of individual fruit per plant (g): this was obtained by dividing total fruit fresh weight per plant by the number of fruit per plant.

Dry weight of individual fruit per plant (g): five fruits of different size (very large, large, medium, small and very small) were selected from each plant and all the selected fruits were chopped in to pieces for hastening the time of drying and they were dried in an oven at a temperature of 72 oC until constant weight was obtained. The dry weight of fruit was added and the sum was divided by the number of fruits to obtain the mean dry weight of individual fruit.

Seed dry weight per fruit (g): Five fruits of different size (very large, large, medium, small and very small) were collected from each randomly selected plants and all the selected fruits seeds were squeezed out of the fruit in to a Petri-dish, and dried in an oven at 72 oC until constant weight was obtained, and the dry weight of seeds was added and the sum is divided by the number of fruits to obtain the mean dry weight of the seeds per fruit.

Total dry weight of fruit per plant (g): this was obtained by multiplying average total number of fruit per plant by the average dry weight of individual fruit.

Total leaf area (cm2): Five plants were randomly selected from the center three rows and the mean total leaf area of a plant in a plot was obtained by adding the total leaf area of the selected plants and then dividing the sum by the number of selected plants. The leaf area was

measured 30 days after the last treatment application date. The area of each leaf was

calculated using a formula developed by (Erik et al., 2004) as: LA= 0.69 x LxW Where: LA= Leaf area, L=Leaf length, W= Leaf width

19

Vegetative dry weight of the plant (g): The vegetative part (aboveground) of the selected plants were harvested and dried in an oven at a temperature of 72 oC until constant weight was

obtained. This was done at the time of the last harvest.

Total dry weight of the plant (g): This was obtained by adding dry weight of individual fruit per plant and vegetative dry weight of the plant.

Seeds number per fruit: this was obtained by collecting five fruits having different size (very large, large, medium, small and very small) from each selected plant and the seed number of each fruit was counted. The mean seed number of a fruit was obtained by adding the seed count of all the selected fruits and then dividing the sum by the number of selected fruits.

Early yield per plant (g): fruits were harvested in the first four weeks out of the total harvest period were considered as early yield and obtained by adding the early yield collected from the selected plants and dividing the sum by the number of selected plants.

Marketable fruit yield per plant (g): this was obtained by adding the marketable fruit yield (fruits > 1 cm3 in volume of pepper) and free from disease, crack and discolor. Obtained from selected plants and then dividing the sum by the number of selected plants (Tsedal, 2004). The total marketable fruit yield per plant was the sum of successive harvests.

Unmarketable fruit yield per plant (g): was obtained by adding undersized fruits (fruits < 1 cm3 in volume of pepper), diseased, cracked and discolored. These were obtained from selected plants and then dividing the sum by the number of selected plants. The total unmarketable fruit yield per plant was the sum of successive harvests.

Marketable fruit number per plant: was obtained by the sum of successive harvests of pepper fruit having > 1cm3 in volume and free from disease, crack and discolor etc.

Unmarketable fruit number per plant: was obtained from the sum of successive harvests of pepper fruit having < 1 cm3 in volume and diseased, cracked, discolored etc.

Total fruit yield per plant (kg): This was obtained by adding average marketable and unmarketable fruit yield per plant of successive harvests.

20

Total fruit yield per hectare (kg): At each harvest, the marketable and unmarketable fruits were harvested from the net harvest area of the plot (4.20 m2) and the sum of marketable and unmarketable fruit yield of successive harvests was converted into hectare.

3.4.2. Fruit quality

Fruit length (cm): this was measured by selecting five fruits having different size (very large, large, medium, small and very small) collecting from each selected plants and the length of each fruits were measured by ruler. The mean length of fruits was obtained by adding the length of all the selected fruits and then dividing the sum by the number of selected fruits.

Fruit diameter (cm): this was measured by selecting five fruits having different size (very large, large, medium, small and very small) from each selected plant and the diameter of each fruit was measured (at the wider portion) by using caliper and the mean value was computed.

Fruit volume (cm3): pepper fruit shape is conical, fruit volume was estimated by selecting five fruits having different size (very large, large, medium, small and very small) collecting from each selected plant and the fruit volume was measured from the length and diameter of the fruit, using the formula d2h/12 (where d and h represents diameter and length, respectively) (Garvey and Hewitt, 1991).

Pericarp thickness (mm): five fruits of different size (very large, large, medium, small and very small) were collected from each selected plant. Each fruits were cut in to two halves though the equator and the thickness of the pericarp was measured by a caliper. The mean thickness of the pericarp was obtained by adding the pericarp thickness of all the selected fruits

and then dividing the sum by the number of selected fruits.

3.5. Data Analysis

The data were subjected to analysis of variance using SAS statistical software (SAS Version 6.12, 1997). Means were compared using the Least Significant Difference (LSD) test at 5% or 1% probability levels. Correlations between parameters were done when seemed necessary.

21

4. RESULTS AND DISCUSSION

4.1 Yield and Yield Components

4.1.1. Fresh and dry weight of individual fruit per plant and seed dry weight per fruit

Fresh and dry weights of individual fruit per plant and seed dry weight per fruit were not significantly affected by the stage of pruning (Table 1). This shows that whether pruning is done at bud or at anthesis or at fruit set, it does not make significant difference on fresh and dry weight of individual fruit per plant and seed dry weight per fruit. However, there was highly

significant (P < 0.01) increase in fresh and dry weight of individual fruit per plant and seed dry weight per plant in response to increased intensity of pruning (Table 1 and Appendix Table 2). Three-reproductive organs pruning improved fresh and dry weight of individual fruits per plant and seed dry weight by about 109.64%, 52.8% and 65% respectively, compared to the unpruned treatment. The increase in fresh and dry fruit weight of individual fruit per plant and seed dry weight per fruit in response to the pruning treatment could be due to the reduction of inter-fruit competition. Similarly, Ali and Kelly (1992) found a similar increase in the size of sweet pepper fruit as the result of removal of flower buds, flowers and set fruits on the first

three flowering nodes. In addition, it is appeared that the enhancement of fresh and dry weight of individual fruit per plant and seed dry weight in response to the pruning treatment could be

due to leaf area increment that maximized light interception and probably assimilate production. Total leaf area was strongly and positively correlated with fresh weight of individual fruit (r = 0.93**), dry weight of individual fruit (r = 0.71**) and seed dry weight per fruit (r = 0.911**) that supported the speculation. In agreement, Tekalign and Hammes (2005b) noted that removing flowers and fruits significantly increased percent dry matter of potato due to the largest proportion of assimilates being diverted to the developing tubers rather than for flower and fruit production. On the contrary, Heuvelink and Buiskool (1995) reported that a decreased sink-source ratio, as a result of fruit or truss pruning, reduced the fraction of dry matter distributed to the fruit. Ho (1979) has explained that as excess assimilate accumulate in the assimilate pool it may be diverted to vegetative growth. Fresh and dry weights of individual fruit per plant and seed dry weight were not significantly affected by the interaction of intensity and stage of pruning.

22

Table 1. Fresh and dry weight of individual fruit per plant, seed dry weight per fruit, total dry weight of fruit per plant and early yield per plant of pepper as affected by stage and intensity of reproductive organs pruning

Treatments

Fresh weight of individual

fruit per plant (g)

Dry weight of individual

fruit per plant (g)

Seed dry weight

per fruit (g )

Total dry weight of fruit per plant (g)

Early yield per plant (g)

Stage Bud 5.73 2.19 0.52 46.68 102 Anthesis 5.51 2.22 0.51 47.28 99 Fruit set 5.73 2.08 0.52 45.28 101 F-test ns ns ns ns ns Intensity Control 4.23d 1.78c 0.40d 54.11a 110a One-RO 5.00c 1.83c 0.47c 48.30b 101b Two-RO 6.71b 2.31b 0.52b 44.50bc 96b Three- RO 8.91a 2.72a 0.66a 38.72c 95b F-test ** ** ** ** ** CV (%) 10.8 10.97 6.91 12.76 8.2 ns and ** refers to non significant at 5% and significant at 1% probability level, respectively. Mean values within column followed by the same letter are not significantly different 1% probability level. RO= Reproductive Organ

4.1.2. Total dry weight of fruit per plant

Total dry weight of fruit per plant was not significantly affected by the stage of pruning but it

was highly significantly (P < 0.01) influenced by intensity of pruning (Table 1 and Appendix Table 2). The highest total dry weight of fruit per plant (54.11 g) was from the control plants and as the intensity of pruning increases it had significantly decreased the total fruit dry weight and the least value (38.72 g) being at three-reproductive organs pruning. This could be due to reduction in dry matter accumulation in the fruit and a decrease fruit number that was not significantly compensated by individual fruit size improvement in response to pruning. The result was in agreement with the observations of Guinn and Mauney (1980), Gifford and Evans (1981) and Nederhoff et al. (1992) where profound increase in source: sink ratio due to intensive pruning reduced dry matter production (source activity). The requirements of the sink organs for photoassimilates regulate the rate of photosynthesis (Ho, 1992). Total dry weight of fruit per plant was negatively correlated (r = -0.49**) with dry weight of individual fruit per

23

plant, which may proved that the compensation of yield loss due to intensive pruning by inverse increase in mean fruit weight is limited in pepper. Similarly, Gifford and Evans (1981) stated that the inhibition of leaf photosynthetic rate after sink removal by means of a hormonal mechanism which influences stomatal or mesophyl resistance and causes the negative feedback controls on photosynthesis. In line with this, Kriedemann et al., (1976) observed a stomatal closure resulting from a build-up of Abscisic acid in the leaf blade of peppers. In some species, fruit removal results in an accumulation of starch grains in the leaves, which may interfere with

the radiant energy reception in the chloroplasts (Schaffer et al., 1986). Besides this Goldschmidt and Huber (1992) stated that accumulation of starch in the plastids may distort the membrane structure of the chloroplast enough to lower gas exchange rates. Total dry weight of

fruit per plant was not significantly affected by the interaction of intensity and stage of pruning.

4.1.3. Total leaf area

Total leaf area of pepper was significantly (P

24

assimilate to the vegetative parts. In agreement with the current finding, Heuvelink and Buiskool (1995) stated that fruit and truss pruning led to higher average fruit weight, heavier stems and leaves and thicker leaves in tomato. In this connection, Tekalign and Hammes (2005a) reported that flowering and fruiting in potato had a reduction effect on the growth and development of above ground vegetative parts because of the higher assimilate demand for reproductive growth since they are strong sinks. There is evidence indicating that after fertilization the developing seed and fruit structures are strong sinks and gain priority over vegetative organs in attracting assimilates (Ho, 1988). The result was also supported by Wien et al. (1989b) who stated that sink removal will not invariably lead to adverse effects on photosynthesis, as most vegetable crops have alternate sinks that can become principal sinks

after fruit removal.

4.1.5. Total dry weight of the plant

Total dry weight of the plant was highly significantly (P

25

4.1.6. Seed number per fruit

Seed number per fruit was highly significantly (P

26

4.1.7. Early yield per plant

Early yield per plant was not significantly affected by the stage of pruning indicating that whether pruning is done at bud, anthesis or fruit set stage; it does not make significant difference on early yield per plant. However, early yield per plant was highly significantly (P

27

potential yield due to pruning that could not be fully compensated by mere increase of an individual fruit size in response to the fruit pruning. The increase in unmarketable fruit yield per plant in two- and three-reproductive organs pruned treatments could be associated with the diversion of more assimilates to the remaining fruits that might have caused physiological disorders. In agreement with the current finding, Dorais and Papadopoulos (2001) indicated that over pruning can cause yield loss and increase physiological disorder like fruit cracking, discolored and diseased which are associated with the rapid movement of water and sugars towards the fruit when cuticle elasticity and resistance are weak during ripening. Similarly,

Morgan and Lennard (2000) stated that if too many fruits are pruned from the plant, those remaining may be more prone to growth disorders such as cracking, blossomend rot (De Kreij, 1992) and as well as fruit deformation (Aloni et al., 1999). Besides to this Aloni et al. (1991) stated that in peppers small, deformed and parthenocarpic fruits develop after sever flower/fruit pruning. In the current study, although it was not quantified the incidences of cracking and deformed pepper fruits were higher in the three-fruit pruned treatment than the other treatments. Marketable and unmarketable fruit yield per plant were not significantly affected by the interaction of intensity and stage of pruning.

4.1.9. Marketable and unmarketable fruit number per plant

Marketable and unmarketable fruit numbers per plant were not significantly affected by the stage of pruning however, both were highly significantly (P < 0.01) decreased by intensity of pruning (Table 3 and Appendix Table 2). The highest marketable (36.44) and unmarketable (3.76) fruit number per plant were obtained from the control while the lowest marketable (16.4) and unmarketable (1.04) fruit number per plant were obtained from the three-reproductive organs pruned treatment. The observed high percentage of unmarketable fruit per plant in the control treatment may be due to the presence of naturally many fruits and high competition

between them for assimilates. In agreement, Aloni et al. (1991) stated that an increase in total number of flowers and fruits has been shown to increase competition for photosynthates and

thus, decrease fruit size. Similarly, Ali and Kelly (1992) stated that the competition for assimilates exerted by older fruit on the lower fruiting nodes of younger fruits caused the reduction of fruit size. Numbers of marketable and unmarketable fruits per plant were not significantly affected by the interaction of intensity and stage of pruning.

28

Table 3. Marketable and unmarketable fruit yield per plant, and number of marketable and unmarketable fruit per plant as affected by stage and intensity of reproductive organs pruning

Treatments

Marketable fruit yield per plant

(g)

Unmarketable fruit yield per

plant (g)

Marketable fruit number

per plant

Unmarketable fruit number

per plant

Total fruit

yield per plant (g)

Total fruit yield per ha (kg)

Stage Bud 160.65 6.49 26.53 2.62 167.14 7965.1 Anthesis 160.57 6.14 27.87 2.35 166.71 7895.5 Fruit set 159.36 6.22 26.7 2.20 165.58 7996.8 F-test ns ns ns ns ns ns Intensity Control 165.59a 4.49b 36.44a 3.76a 170.08a 8099.50a One-RO 170.63a 4.34b 31.96b 3.24b 174.94a 8334.40a Two-RO 153.23b 8.06a 22.93c 1.51c 161.29b 7832.80b Three-RO 151.30b 8.24a 16.80d 1.04d 159.54b 7543.20b F-test ** ** ** ** ** ** CV (%) 5.34 11.2 11.6 17.69 4.54 4.32

ns and ** refers to non significant at 5% and significant at 1% probability level, respectively. Meanvalues within column followed by the same letter are not significantly different at 1% probability level. RO = Reproductive Organs

4.1.10. Total fruit yield per plant and per hectare

Total fruit yield per plant and per hectare were not significantly affected by the stage of pruning. However, both parameters were highly significantly (P < 0.01) influenced by intensity of pruning (Table 3 and Appendix Table 2). The highest (174.94 g) total fruit yield per plant was obtained from one-reproductive organ pruned treatment and it was statistically at par with the control treatment. The lowest (159.54 g) was obtained from the three-reproductive organs pruned treatment, which was statistically at par with the two-reproductive organs

pruned treatment. In the same manner, the highest (8334.4 kg) total fruit yield per hectare was obtained from one-reproductive organ pruned treatment and statistically at par with the control and the lowest (7543.20 kg) was obtained from three-reproductive organ pruned treatment. The observed reduction in total fruit yield per plant and per ha in response to an increased intensity of fruit pruning could be due to a significant reduction in fruit number and a

29

concomitant loss in potential yield. The loss in total yield due to fruit number reduction could not be significantly compensated by an increase in fruit size in response to the pruning treatment. Similarly, Marcelis (1996) showed that distribution of assimilates among sinks is primarily regulated by the sink strength and generative sink strength is assumed to be proportional to the number of fruits. On the other hand, Heuvelink (1997) stated that the reduction in total fruit yield per plant can be explained by a decreased partitioning of assimilates to the fruits due to the reduced generative sink strength as a result of fruit pruning.

4.2 Fruit Quality

4.2.1. Fruit length

Fruit length of pepper was highly significantly (P

30

4.2.3 Fruit volume

Fruit volume of pepper was significantly (P < 0.05) affected by the interaction effects of stage and intensity of fruit pruning (Table 4 and Appendix Table 2). All the pruning treatments tended towards higher fruit volume than the control, the highest fruit volume (33.98 cm3) was found in the combination of three fruit pruned at anthesis stage and the lowest (9.96 cm3) was from the control treatment. Fruit volume was not significantly correlated with number of seed per fruit. Such result may have appeared because reducing the number of fruit allows the plant to distribute assimilates to a lesser number of fruit which will attain a bigger size. Therefore, potential fruit size may be determined by factors regulating the cell number and seed number rather than the seed number per pod. As parthenocarpic fruit still can grow to appreciable size, seed number may not be a suitable measure of sink size, which is defined as physical constraint

of sink strength (Ho, 1992).

4.2.4. Pericarp thickness of fruit

Pericarp thickness of pepper fruit was significantly (P

31

Table 4. The interaction effect of stage and intensity of reproductive organs pruning on fruit length, fruit diameter, fruit volume and pericarp thickness of pepper fruit

Treatment

Fruit length (cm)

Fruit diameter (cm)

Fruit volume (cm3)

Pericarp thickness (mm)

Stage of Level of Pruning pruning Bud Control 9.44j 1.96h-j 10.59g-i 2.44i

One- RO 11.71e-i 2.36d-f 18.20d 2.58g-i Two- RO 12.34c-i 2.47c-f 19.50d 2.69e-i Three- RO 12.33d-i 2.49b-f 27.69bc 2.96c-f

Anthesis Control 9.61j 1.97g-j 10.53hi 2.62f-i One- RO 11.27i 2.22f-i 15.29d-h 2.73c-h Two- RO 11.53f-i 2.34ef 15.61d-f 2.70d-i Three- RO 13.14b-d 2.75a-c 33.98a 3.10bc

Fruit set Control 9.82j 1.90j 9.96i 2.49hi One- RO 11.34hi 1.94ij 11.91f-i 2.90c-g Two- RO 11.36g-i 1.94ij 12.06e-i 2.94c-f Three- RO 14.64a 2.98a 26.17c 3.65a

F-test * ** * * CV (%) 6.12 8.01 16.34 6.25

* and ** refers to significant at 5% and significant at 1% significance level, respectively. Interaction means followed by the same letter are not significantly different at the prescribed level of significance. RO = Reproductive Organs

32

5. SUMMARY AND CONCLUSIONS

The continuous growth of pepper plant in tropics increase the number of fruit per plants and this in turn increases the potential for competition between fruits with consequent reduction in fruit size. Field experiment was conducted on farmers field from November 2009 to June 2010 at Humbo, Southern Ethiopia. The objective of the study was to assess the effects of stage and intensity of reproductive organs pruning on yield and quality of pepper. Four levels of pruning

(control, one-reproductive organ, two- reproductive organs and three- reproductive organs) and three stages of pruning (bud, anthesis and fruit set), were arranged in factorial combination in Randomized Complete Block Design with three replications. Pepper cultivar called Marekofana with spacing of 70 cm x 30 cm was used.

In the evaluation of source-sink relationships of pepper, stage of pruning had a little effect than intensity of pruning. Total leaf area of pepper was highly significantly (P < 0.01) affected by the interaction effects of stage and intensity of pruning. The highest total leaf area (6945.88 cm2) was obtained three-reproductive organs were pruned at fruit set stage. Fresh weight of individual fruit per plant, dry weight of individual fruit per plant , seed dry weight per fruit, total dry weight of fruit per plant, early yield per plant, marketable fruit yield per plant,

unmarketable fruit yield per plant, number of marketable fruit per plant, number of unmarketable fruit per plant, total fruit yield per plant and total fruit yield per hectare were not

significantly influenced by stage of pruning, but they were highly significantly (P < 0.01) influenced by intensity of pruning.

Fresh and dry weight of individual fruit per plant and seed dry weight per fruit were highly significantly (P < 0.01) increased in response to increased intensity of pruning. Three- reproductive organs pruning improved fresh and dry weight of individual fruits per plant and seed dry weight per fruit by about 109.64%, 52.8% and 65% respectively, compared to the unpruned treatment. The highest total dry weight of fruit per plant (54.11 g) was from the control plants and as the intensity of pruning increases it had highly significantly (P < 0.01) decreased and the least value (38.72 g) being at three- reproductive organs pruning.

33

Vegetative dry weight of the plant and total dry weight of the plant were highly significantly (P < 0.01) affected by the interaction effect of stage and intensity of fruit pruning. The highest vegetative dry weight (71.87 g) per plant and total dry weight (110.59 g) of the plant were obtained three- reproductive organs were removed at anthesis stage and the lowest (56.9 g) and (102.18 g) were obtained from the control respectively. Seed number per fruit was highly significantly (P < 0.01) affected by the interaction effects of stage and intensity of reproductive organ pruning. The highest mean seed number per fruit (148.21) was recorded two- reproductive organs were pruned at bud stage while the lowest seed number per fruit (100.15) was obtained from the control

Early yield per plant was highly significantly (P < 0.01) influenced by intensity of pruning. The highest early yield per plant (110 g) was obtained from the control and significant reduction was observed with reproductive organ pruning although one-, two- and three- reproductive organs pruning gave comparable yield. Marketable and unmarketable fruit yield per plant were not significantly affected by the stage of pruning. However, fruit pruning highly significantly (P

34

hectare (7543.20 kg) were obtained from the three- reproductive organs pruned treatment.

Fruit length, fruit volume and pericarp thickness of fruit were significantly (P < 0.05) affected by the interaction effects of stage and intensity of reproductive organs pruning. The combination of three-reproductive organs pruned at fruit set stage gave the longest fruit length (14.64 cm) and the thickest pericarp (3.65 mm) and the shortest (9.44 cm) and thinnest (2.44 mm) fruits were obtained from the control respectively. With the same manner the highest fruit volume (33.98 cm3) was obtained in the combination of three- reproductive organs removed at anthesis stage and the lowest (9.96 cm3) was obtained from the control. Fruit diameter was highly significantly (P < 0.01) affected by the interaction effects of stage and intensity of reproductive organs pruning. The combination of three reproductive organs removed at fruit set stage produced fruit with the largest (2.98 cm) fruit diameter and lowest (1.9 cm) was obtained from the control.

In all the parameters considered, the effect of source-sink relationships on the performance of pepper was thoroughly investigated. Concerning stage of pruning, even though it is difficult to decide the optimum time of pruning for better yield and quality it can be concluded that stage of pruning had a lesser effect for yield components of pepper but in quality parameters it was

significantly correlated with intensity of pruning. All the parameters considered were affected by intensity of reproductive organs pruning. Therefore, for the determination of yield and

quality parameters of pepper, pruning intensity had a better magnitude effect than stage of pruning. Regardless of the physical quality parameters of pepper pruning three- reproductive organs at fruit set and anthesis stage gave the better quality at the expense of marketable fruit yield per plant, total fruit yield per hectare and total dry weight of fruit per plant. Therefore, pruning one reproductive organ gave better yield and quality without the loss of marketable and total fruit yield per plant. However, to come up with a conclusive recommendation for the area, similar experiments including economic feasibility needs to be carried out across location.

35

6. REFERENCES

Ali, A. and W. Kelly, 1992. The effects of inter fruit competition on the size of sweet pepper (Capsicum annuum L.) fruit. Journal of Scientia Horticulturae. 52: 69-76.

Aloni, B., E. Pressman and L. Karni, 1999. The effect of fruit load, defoliation and night temperature on the morphology of pepper flowers and on fruit shape. Journal of Annals of Botany. 83: 529-534.

Aloni, B., L. Karni, Z. Zaidman and A.A. Schaffer, 1996. Changes of carbohydrates in pepper (Capsicum annuum L.) flowers in relation to their abscission under different shading regimes. Journal of Annals of Botany. 78: 163-168.

Aloni, B., T. Pashkar and L. Karni, 1991. Partitioning of [14C] sucrose and acid invertase activity in reproductive organs of pepper plants in relation to their abscission under heat stress. Journal of Annals of Botany. 67: 371-377. Amroszczyk, F. and S. Cebula, 2003. The effect of pruning and training on the productivity of eggplant (Solanum melongena L.) in greenhouse production. Journal of Acta Agraria et Silvestria. 41: 71-81.

Andriolo, J., L. Ludke, T. Duarte and E. Skrebsky, 2000. Fruit position and its effects on dry matter distribution on tomato plants. Journal of Sciencia Rural. 30: 235-240.

Atherton, J. and J. Rudich, 1986. The tomato crop. A scientific basis for improvement. Chapman and Hall, London. pp.167-200.

Bangerth F., 1989. Dominance among fruits/sinks and the search for a correlative signal. Journal of Physiologia Plantarum. 76: 608-614.

Bangerth, F. and L.C. Ho, 1984. Fruit position and fruit set sequence in a truss as factors determining final size of tomato fruit. Journal of Annals of Botany. 53: 315-319. Batlang, U., 2008. Benzyladenine plus gibberellins (GA4+7) increase fruit size and yield in green house grown hot pepper (Capsicum annum L.). Journal of Biological Sciences. 25: 35-38.

Batlang, U., V. E. Emongor and F. Pule-Meulenberg, 2006. Effect of benzyladenine plus gibberellic acid on yield and yield components of cucumber (Cucumis sativus L. cv.tempo). Journal of Agronomy. 5(3): 418-423.

Bertin, N., H. Gautier and C. Roche, 2002. Number of cells in tomato fruit depending on fruit position and source-sink balance during plant development. Journal of Plant Growth Regulators. 36: 105-112.

36

Berke, T., L.L. Black, N.S. Taleker, J.F. Wang and P. Gniffke, 2005. Suggested cultural practice for chilli peppers. Asian vegetable research and development center pepper project. Taiwan Agricultural publication. pp.620.

Bhatt, R. and N. Rao, 1989. Effect of deblossoming on photosynthesis and dry matter distribution in bell pepper (Capsicum annuum L.). Journal of Photosynthetica. 23: 466-471.

Bhatt, R. and N. Rao, 1993. Partitioning of [14C] photosynthate in fruiting and deblossomed bell pepper plants. Indian Journal of Experimental Botany. 31: 389-391. Bhatt, R. and N. Rao, 1997. Growth and photosynthesis in bell pepper as affected by sink manipulation. Journal of Biologia Plantarum. 39: 437-439.

Bohner, J. and F. Bangerth, 1988. Effects of fruit-set sequence and defoliation on cell number, cell size and hormone levels of tomato fruit (Lycopesicon esculentum Mill.) with in a truss. Journal of Plant Growth Regulators. 7: 141-155. Bosland, P. W. and Votava, E. J. 2000. Peppers: Vegetable and Spice Capsicums. Crop Production Science in Horticulture. CABI Publishers. pp304.

Cantliffe, D., 1974. Promotion of fruit set and reduction of seed number in pollinated fruit of cucumber by chlorflurenol. Journal of Horticultural Science. 9: 577-578.

Cebula, S. and A. Kalisz, 2001. The effect of side shoots pruning on the growth and fruiting of sweet pepper plants trained to one main shoot in greenhouse production. Veg