MARDI Res. J. 18(2)(1990): 19 1-196

Response of papaya (Carica papala L.) to limited soil moisture atreproductive stage[Tindak balas betik (CaricapapoyaL.) terhadap kandungan airtanahyangterhadpada peringkat reprodukti fl

M. Masri*, A. S. Razak**, and M. Z. Ghazalli***

Key words: soil moisture deficit, stress, growth, papaya

AbstrakKajian terhadap kesan p€ngurangan air tanah pada peringkat reproduktif betik(Carba papaya L.) varieti Eksotika telah dijalankan. Perlakuan terdiri daripadategasan, tadahan hujan dan pengairan. Didapati bahawa kadar penambahantinggi dan garis pusat batang bagi perlakuan tegasan ialah masing-masing52Vodan 36Vo lebih rendah berbandingdengan perlakuan pengairan. Bilanganpelepah hidup sepokok pula5OVo lebih rendah. Pengurangan kandungan airtanah pada pcrlakuan tegasanjuga telah mengurangkan bilangan bunga danbuah masing-masing sebanyakS6Vo dan 58% berbanding dengan perlakuanpengairan. Tegasan airjuga didapati merencatkan pertumbuhan dan pembesaranbuah betik.

AbstractThe effects ofdepleting soil moisture at the reproductive stage on papaya(Carica papaya L.), Eksotika variety, were studied under field conditions.Treatments consisted of stress (not irrigated and sheltered), rainfed (not irrigatedbut exposed to rainfall) and irrigated. In the stress treatment, height and trunkdiameter increments were 52Vo and 36Vo resp€ctively less than those of irrigatedplants. Consequently, plant under stress treatment had 50Vo fewer attachedleaves per tree. Water deficit significantly reduced number of flowers andfruit by 86Vo and 58% respectively. Water stress also retarded growth anddevelopment of papaya fruit.

Introduction year to year (Nieuwolt 1982). TheseConsiderable attention is currently given to variations could lead to drought of varyingthe soil moisture level as a factor that can intensities during the cropping season.affect fruit production in Malaysia. This is The effects of drought on crop growthdue to the varying rainfall duration and and development are a consequence ofdistribution in this country. The diumal, ffioqphological and physiological alterationsseasonal and annual distributions of rainfall of plant growth. Therefore, the overallvary widely from region to region and from response of plants to water stress is thetFruits Research Division, MARDI, I-ot. 9, Ban&r Baru l-aka Temin, 06050 Bukit Kayu Hitam, Malaysie

"Fruits Research Division, MARDI, P. O. Box l23o1,50774 Kuala l,umpur, Malaysia

"f Basic Research Division, MARDI, P. O. Box lZ30l,50'174 Kuala Lumpur, MalaysiaAuthors' full nemes: Masri Muhamad, Abdul Razak Shaari and Mohd. Zki Ghazalli**Present address: Agriculture Attache', Embassy of Malaysia, Via Nomenhna 87,00162 Rome, Italy@Malaysian Agricultural Research and Development Institute 1990

191

Response of papaya to limited moisture

Ptate 1. Rainfall was excfuded from treated. plots using plastic covers installed along the tree rows

f$*

result of complex interactions of manyphysiological processes.

Studies on the effects of water str€ss ongrowth and development of papaya underMalaysian conditions are relatively limited.Chan and Tee (1975) reported that dry spellscaused abortions of floral and fruitstructure,s, leading to sterile phases andfruiting skips along the stem. In anotherstudy, Ong and Chan (1983) found thathigh temperature interacted with dry spellresulted in flucxuations of fruit yield of threetypes ofpapaya. Constant availability ofsoil moisture was associated withcontinuous growth of papaya which resultedin the regular production of flowers and fruit(Anon.1982).

In this study, the effects ofdepletingthe soil moisture at the reproductive stageon growth, flowering and fruit set ofEksotika papaya were evaluated under fieldconditions.

Materials and methodsSeeds of papaya variety Eksotika were sownin 15 cm x 23 cm polyethylene bags andwere raised in the nursery with a 5OVoshade level. At 6 weeks after sowing, the

L92

seedlings were transplanted to field plotsarranged in a randomis€d complete blockdesign with four replications. The plantingdistance was 1.8 m x 3 m and eachrepiicated plot consisted of four sample treeswith adequate border rows. All plots weredrip irrigated to ensure uniform andvigorous crop growth before the varioustreatments were imposed.

Three treatments namely, stress (notinigated and sheltered), rainfed (notirrigated but exposed to rainfall) andirrigated, were established at the fourthmonth after transplanting. Soil moisturedeficit in the stress treatment was induced bywithholding irrigation as well as excludingrain water using transparent plastic sheetcovers. These sheets were supported bywooden frames installed 1-m high along thetree rows. Such structures permitted free airmovement under the covers (Plate 1).Trenches of l-m wide and L-m deep wereconstructed to prevent interference of soilmoisture among plots.

Soil moisture in the top 30 cm soildepth was monitored every 2 days by usingthe neutron scattering method (HydroprobeModel ELE-503 DR). The average readings

Soil

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M. Masri. A. S. Razak and M. Z. Ghazalli

Rainfed

tsD 0.05

-240

0 4 8 1 2 1 6 2 0 t 4 z 6

Days after treetmeDts were imposed

Figure 1. Changes in soil moisture tension in the top 0-30 cm soil depth as affected by the treatments

and rainfall

moisture lension ftPa)

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from two accsss tub€s installed in eachplot were considered as one replication.Data on the volumetric soil moisture were

transformed into soil moisture tension CI/s)using the soil moisture characteristic curvedeveloped by Wong (1981).

Weekly recordings of vegetativegrowth parameters such as plant height,stem diameter and number of attached leavesstarted immediately after the treatmenlswere imposed. Plant height was measured

from the collar at the bas€ of the trunk to thetip of the youngest shoot. Stem diameterwas determined at 15 cm above the collarusing vemier calipers. Ten healthy fruit pertreatment separated as hermaphrodite andfemale were tagged 1 day after anthesisand their lengths and circumferences weremonitored so ils to quantify the effects ofstress on fruit growth and development.Treatments of differential moisture levelswere terminated 30 days after they were

Irrigated

193

Response of papaya to limited moisture

Fleight increnrcnt

(cm/month)

Trunk diamete r incremenl(cm/month)

No. of .ttrched lerves/tree

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imposed. After the 14th day of withholdingwater. the Ws in the stress treatmentincreased tremendously from -65 kPa to-260 kPa. This suggested that the plants inthe stress treatment experienced moisturedeficit. Visual symptoms of wilting werefirst noticed in these plants on the 14th dayafter withholding water. The wilting ordrooping of leaves in mid-aftemoon is asign of plants beginning to experiencemoisture deficit (Masri and Boote 1987).

Plant height and trunk size were used tocharacterise vegetative growth of papayatrees. The height and trunk diameterincrements of plants under stress treatmentwere 52Vo and 36Vo respectively, which aresignificantly lower (p = 0.05) than those inthe irrigated treatment (Figure 2). Thissuggested that the growth of papaya treeswas retarded under moisture strqssconditions. The lower height and trunkdiameter increments in stress plantscorresponded closely to the higher Ws values

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Figure 2. Effects of soil moisture deficit on vegetative grov'th of papaya

imposed and reproductive parameters suchas number of flowers and fruit wererecorded.

Reults and discussionPoor water availability in the soil and hightranspiration result in a negative waterbalance. Plants suffer moisture stress whenthe loss of water by plants is greater than itsuptake. In this experiment, moisture stresswas defined as a function of soil moisturetension fVs). For most crop species,optimum Vs are in the range of -20 to -50

kPa (Mengel and Kirkby 1982).In the irrigated and rainfed treatments,

the Vs flucluated between -12 and -18

kPa(Figure 1), indicating that th€ plantsdid not suffer any moisture deficit. Bycontrast, the rys in the stress treatmentgradually increased and were significantly(p = 0.05) higher (-65 kPa) than the Vs inthe rainfed (-20 kPa) and irrigated plots (-16kPa) 14 days after the treatments were

194

(Figure 1). In comparison, height and trunkdiameter increments of plants under rainfedtreatment did not differ significantly

@ = 0.05) from that of the irrigated plansand this also corresponded closely to theirraspective Vs values.

Limited soil moisture causedsignificant (p = 0.05) reduction in leafnumber (Figure 2,). Planls under moisturestress had 5OVo fewer attached leaves pertre€ than that of the irrigated plans. Thefewer leaves in the stress treatment weredue to premature senesc€nce. Fewer leavesp€r tree will mean a loss of photosyntheticsurface for the plant. Increased leafsenescen@ under water stress was alsoreported in corn (Zea mays L.) (Sharp andDavies 1985), and in com and soybean(Glycine rutx L.) by Masri and Boote(1e88).

As for the reproductive parameters,plants under rainfed and stress treatmentshad significantly fewer flowers per tre€compared with irrigated plants (Figure 3).Moisture stress caused 35% and {J6Voreduction in flower number in the rainfedand stress treatments respectively ascompared with the irrigated treatment.Similarly, fruit number in the stress andrainfed treatments were 58Vo and 45Vorespectively fewer compared with theirrigated plants (Figure 3).The reduction inthe number of flowers and fruit may beattributed to the exiessive abortion. It hasbeen reported that dry spells cause abortionof floral and fruit struclures of papaya(Chan and Tee 1975).

Moderate water deficit as depicted bythe rainfed treatment did not significantlyretard vegetative growth during thereproductive stage. These were manifestedby the non-significant differences(p = 0.05) in height and trunk sizeincrements as well as leaf number per tre€between the rainfed and irrigatedtreatments. However, the effects weresignificant (p = 0.05) for reproductiveparameters (number of flowers and fruit). Itappears that reproductive parameters were

M. Masri. A. S. Razak and M. Z. Ghazal|i

No. of flowers/tree No. of fruiVtree

l s l

Irrigated

Rainfed

Stress

Figure 3. Effects of soil moisture deficit onnumber of flowers and fruit of papaya

more sensitive to water stress comparedwith vegetative parameters during this stageof crop growth (4-5 months aftertransplanting).

Data on the weekly increment in fruitlength and circumference of each treatmcntare shown in Figure 4. T\e rates of lcngthand circumference increment in the rainfedand stress treatments are slower than thoscof the irrigated. This indicated that the ratesof fruit growth and developmenl wcreslower under water stress conditions.

'lhe

slower rate of fruit growth was true for bothfemale and hermaphrodite fruits.

ConclusionThe induced soil moisture stressconditions during the reproductive growthstage had caused significant reduction invegetative and reproductive growth ofpapaya. Plant beight and trunk diameterincrements were significantly reduced andpremature leaf senescenc€ was excessive.Flower production and fruit set were

25 T

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Response of papaya to limited moisture

Fernale fruit

Circumference (cm) kngth (cn)

:

Hermaphrodite fmit

Circumference (cm) l-ength (cm)

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Drys rfter tre.tments were imPosed

Figure 4. Fruit growth and development as affectedby different soil moisture levels

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greatly suppressed while fruit growth anddevelopment were relarded.

AcknowledgementThe authors gratefully acknowledge thetechnical assistance of Mr Ali Sulaiman.

ReferencesAnon. (1982). Upland crops condition. Ilre

Philippines recontntends for irrigation watermanagementYol.Z, p. 64. [-os Banos:Philippine Council for Agric. Resource Res.

Chan, Y. K. and Tee, T. S. (197-5). Studies on thesunrise solo papaya in Malaysia. IvIARDI Rep.No. 36 lO p. Serdang: MARDI

Masri, B. M. and Boote, K. J. (1987). Kesankekurangan air terhadap pertumbuhan daundan fotosintesis tanaman jagung dan kacangsoya. MARDI Res. Bull. 15(2): 73-8

Accepted for publication on 13 June 1990

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o------o Irrigatedo o Rainfed" - sfess

_ (1988). Effects of water stress on leaf areaindex, crop growth rate and dry matteraccumulation of field-grown corn andsoybean. MARDI Res. J. 16(l): 5741

Mengel, K. and Kirkby, E. A. (1982). Principles ofplant ruttrition 665 p. Swiuerland: Inter.Potash Inst.

Nieuwolt, S. (1982). Climate and agriculturalplanning in Peninsular Malaysia (SpecialReport) p. 139. Serdang: MARDI

Ong, H. T. and Chan, Y. K. (1983). Cl imaticinfluence on the yields of fruit numbcr inthree types of Carica papaya in Serdang,Malaysia. Pertanika 6(2) : 7 -'1,4

Sharp, R. E. and Davies, W. J. (198-5). Root growthand water uptake by maize in drying soils. J.Exp. Bot.36. ' 1141--56

Wong, N. C. (1981). Detai led soi l survey of theMARDI B€rtam Station, Seberang Perai, AnnRep., Soil Science Branch, MARDI (mimeo.)

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