Philippine Journal of Crop Science (PJCS) April 2017, 42 (1):69-74 Copyright 2017, Crop Science Society of the Philippines

Optimizing Seed Potato Production by Aeroponics in China

Kexiu Wang1, 2, Wei He 2, Yingwei Ai1, Jianjun Hu2, Kaiyun Xie4, Mingxia Tang2, Yuming Wang2

and Peter Vander Zaag 3*

1Key Laboratory of Bio-resources and Eco-environment (Ministry of Education), College of Life Sciences, Si-chuan University, Chengdu 610064, P. R. China; 2 Crop Research Institute of SAAS, China; 3 Yunnan Normal University, Kunming, China, 4International Potato Center. *Corresponding author, pvzaag@gmail.com

Aeroponics is being enthusiastically adopted by many private companies and public institutions in China as a viable means to produce minitubers. A series of experiments were conducted, with two contrasting varieties: Chuanyu 117 and Mira, to help refine the techniques and to strive for greater productivity. Experiments were conducted at Chengdu, Sichuan during the spring season from February to June and the autumn season from late September to February. Large differences were observed between nutrient solutions tested. The cheapest MS based treatment with NH4Cl as the nitrogen source produced the highest tuber number per plant. The MS based solution with NH4NO3 as the nitrogen source yielded the highest tuber weight per unit area. Misting the nutrient solution for 30 sec every 10 min appears to be better than doing it at a 20-min interval. For the variety Chuanyu 117, the 20-min interval had a dramatic negative effect in contrast to Mira which was minimally affected. Maximum tuber number per unit area was obtained with plant densities between 54 and 80 plants m-2. Harvesting the tubers at 2-wk interval during the bulking period did significantly improved yields of Chuanyu 117 but not Mira. Assessing all 3 experiments, considering the best treatments, the tuber number per plant ranged 22-34 for Chuanyu 117 and 23-28 tubers per plant for Mira. The main limitations that need to be overcome are the management of the plants so that they develop adequate haulm growth to support tuber growth through nutrient and hormonal manipulation for both the spring and autumn seasons, which have contrasting climatic conditions.

Keywords: aeroponics, minitubers, seed potato production, tuber number, tuber yield

INTRODUCTION Aeroponics as a way to grow virus free basic seed has rapidly gained acceptance in China by both the private and public sectors (He et al. 2014). National government financial support and incentives have spurred on the rapid adoption. This was initiated after the devastating earthquake that struck Sichuan in May 2008. This received international attention and financial support from the World Bank and technical support from the International Potato Center to assist the farmers of Sichuan who survived the earthquake to receive clean planting materials as soon as possible. Aeroponics was adopted as a way to accomplish this mandate. The national priority is to produce clean seed and multiply it only for 3 field generations as seed. This strategy has helped increase national average potato yields and the area under production (He et al. 2008). With the rapid adoption, little attention was given as to how it maximizes productivi-ty in the various ecological zones of China. Sichuan is a major potato growing province with basically 2 potato greenhouse growing seasons. The Spring crop going from the cool winter into a hot summer and an Autumn crop going from a hot summer into a cool winter. Numerous challenges faced are the abiotic stresses that occur in reverse order between the 2 seasons which includes light intensity, temperature and daylength and their

influence on hormone levels and plant growth (Demagante and Vander Zaag 1988; Vreugdenhil and Struik 1989). The variables that need to be addressed include optimal nutrient solutions, plant densities and the number of harvests that is optimal (Tierno et al. 2013). Published data to date showed that productivity per plant ranges 12-45 minitubers per plant (Mateus-Rodriguez et al. 2013). The major objective of this series of experiments was to optimize potato tuber production for two widely grown varieties in Sichuan. The influence of various nutrient solutions, frequency of misting the roots, plant density and frequency of harvest were evaluated.

MATERIALS AND METHODS Climatic Conditions The minimum and maximum monthly average temperatures, day length and solar radiation for the Chengdu plains of Sichuan Province, China (Latitude 30N and altitude 500 m above sea level) for the years 2011-2013 are presented in Figure 1. Noteworthy is the extremely high temperatures from June - August. It is under these conditions that the experiments were conducted in the Spring and Autumn seasons in a semi controlled temperature greenhouse in the Campus of the Sichuan Academy of Agricultural Sciences. Heating was done as needed. Fans were

Full Paper

K Wang et al.

used for cooling and a shade cloth that can be automatically rolled over the greenhouse not only provide cooling effect but also reduced light entry by 33%. Experimental Facilities and Design Figures 2 and 3 showed how the facilities were designed and operated. The overall beds were 4 m x 1.2 m with a vertical depth of 45 cm inside the bed for Experiments 1 and 3. Within each bed four 0.6m x 2m treatments were established with partitions separating each treatment inside the bed. Four rows of nozzles, which were staggered, spaced 40 cm apart were placed at the bottom of each bed. Plants were spaced at 10 cm x 15 cm with a total of 65 plants per treat-ment, comprising of 5 rows of 13 plants. A border empty space was kept on the back and front of each treatment. For Experiment 2, the design was 0.6m x 0.9 m plot size per treatment. Other details are the same as Experiments 1 and 3. Chemical composition of nutrient solutions used for experiments 2 and 3 are listed in Table 1. All nutrient solutions were renewed weekly. From 28 days after establishment, 80 ppm Propamocarb hydrochloride (722 g L-1) along with 50 ppm Streptomycin (72% ai.) were added to the nutrient solution every week to control fungi and bacteria, respectively. No foliar sprays were required for these greenhouse grown experiments. Treatments were arranged using CRD with 3 replications. Data on tuber number and tuber weight were collected and analyzed. Plant Materials and Varieties Virus-free in vitro plantlets were multiplied and placed in hydroponic culture for hardening and for growing uniform and sturdy plants that are fit for transplanting. Apical cuttings with simple leaves were excised from this plant and placed in the aeroponic system to root, grow and develop tubers. It takes about 5 d for the plants to root. Once the plants were well established, the lower 3-4 compound leaves were removed and the plant was pulled down to have more nodes available for stolon production. Five extra plants were planted as possible replacement in case any plant did not grow well at 3 wk after planting. The variety Chuanyu 117, which originated from CIP germplasm with S. Andigena background, is sensitive to high temperatures. The European cultivar, Mira, is more adapted to higher temperatures. Both cultivars, which are widely grown in Sichuan because of their resistance to P. Infestans, were utilized in all experiments. Experiment 1: Nutrient Solution Composition This experiment was done in both the Spring (January 29 to June 3, 2011) and in the Autumn seasons (September 25 to January 15, 2012). Four nutrient solutions with MS based micronutrients and pH of 5.5-6.0 were evaluated (Murashige and Schoog 1962). Electrical Conductivity (EC) was 1.7-4.8 ms•cm-1.There were 4 macronutrients combinations (Table1). Nutrient Solution III, included ammonium chloride as the nitrogen source while the other 3 treat-ments used ammonium nitrate.

Experiment 2: Plant Density Plant densities established were: 16, 26, 44, 54, 63, 80, and 95 plants m-2. Nutrient solution II was used in this experiment (Table 1). The plot size/treatment was altered in this Experiment to 60 cm x 90 cm. The aeroponics system, management, operation including frequency and duration of misting was the same as in Experiment 1. The Experiment was planted on

Compound Nutrient Solution

I II III IV

NH4NO3 1.25 2.5 0 3.75

NH4Cl 0 0 4.99 0

KH2PO4 0.9 1.8 1.8 2.7

KNO3 8.85 17.7 17.7 26.55

MgSO4·7H2O 0.7 1.4 1.4 2.1

Ca(NO3)·4H2O 0.8 1.6 1.6 2.4

NaCl 0.65 1.3 0 1.95

Initial EC (dS/ m) 1.7 3.2 3.5 4.8

Table 1. Chemical composition of macronutrients of the 4 different nutrient solutions in experiment 1

Figure 1. Minimum and maximum monthly average temperatures, day length, and solar radiation in Chengdu plains of Sichuan Province (2011-2013)

Aeroponics production of seed potato 70

September 22, 2011 and tubers were harvested on December 10 and 24 and final harvest was on January 10, 2012. Experiment 3: Misting and Harvesting Frequency Treatments included misting for 30 sec every 10 and 20 min. Nutrient solution II was used in this experiment, which started on October 16, 2012. At 90 d and every 2 wk thereafter, tubers greater than 3 g were harvested. The final harvest was on February 11, 2013.

RESULTS Experiment 1: Nutrient Solution Composition Significant differences were obtained both for tuber number and tuber weight per unit area and per plant (Table 2). Nutrient solution III produced the highest overall tuber number in both seasons with both varieties. Nutrient solution II and IV were similar and a distant second for tuber number (Table 2). The variety Mira did best in the Spring season going into longer hotter days. Chuanyu 117 did best in the Autumn season as the temperature decreased and days be-came shorter. In general, the tuber number per plant was low with only Nutrient Solution III having an over-all average that exceeds 20 tubers per plant. Experiment 2: Plant Density Plant density had a very dramatic influence on both tuber number and weight produced per unit area and on a per plant basis (Figure 4). On a unit area basis, 63 plants m-2 was the optimum for tuber weight produced per unit area. On a per plant basis the lower densities produced more tubers per plant (Figure 4). Chuanyu 117 did produce significantly more tubers than Mira during this Autumn season with the 5 lowest densities all producing more than 25 tubers per plant. Experiment 3: Misting and Harvesting Frequency During the Autumn season experiment, there was only a slight benefit from doing 3 bi-weekly harvests as compared to doing only a single harvest of tubers

(Table 3). Chuanyu 117 was only slightly more responsive to the periodic removal of greater than 3 g tubers. At the final harvest, all tubers which had formed, were harvested. Many were less than 2 g. Mira produced fewer tubers per plant compared to Chuanyu117. Decreasing the misting frequency from every 10 min to every 20 min was detrimental for Chuanyu 117 but not so for Mira (Figure 5). Chuanyu 117 produced an average of over 30 tubers per plant while Mira produced 20-22 tubers per plant.

DISCUSSION Tuber yield per plant obtained in our aeroponics experiments were similar with the results already published (Chiipanthenga et al. 2012; Farran and Mingo-Castel 2006; Otazú 2010). In our first Experiment, the 4 nutrient solutions had varied levels of EC. Based on results by Chang et al. (2011) some of our solutions may have had EC levels that were too high. This would have inhibited the plants from optimally utilizing the nutrients provided, especially in Nutrient Solution IV. Chang et al. (2011) did show strong varietal differences to EC levels in the solution. We have not yet determined varietal response to EC levels. It may well be that nutrient solutions II and III could have given higher tuber yield had the EC been adjusted downward to around 2 mmol-1. Chang et al. ( 2011) showed that the higher the EC, the greater is the uptake of K with the reverse trend for Ca and Mg and that tuberization was delayed. We will need to fully understand the consequences of EC levels for our varieties being grown aeroponically. Higher plant densities can lead to more foliar disease and lower light availability per plant (Farran and Mingo-Castel 2006). At lower plant densities, failure to make full use of light could reduce potential yield. In the autumn season in Sichuan, plant growth is generally less. Shorter days and decreasing temperatures help induce early tuberization (Figure 1). But in spring, the

Figure 2. Schematic of aeroponic production system. Figure 3. Potato plants growing in aeroponics in the experimental greenhouse

71 K Wang et al.

temperature is high in the later period of the plant life cycle and delayed the tuber initiation. Warm root zone temperature and air temperature sharply reduced mini-tuber number and weight (Levy and Veilleux 2007; Menzel 1980; Oraby et al. 2015), So it is important to

cool the nutrient solution to 18℃ and get higher tuber yield. Choosing proper varieties (such as middle and early maturity varieties in spring, and middle and late maturing varieties in autumn) is important. Mira, a Tu-berosum type does best in the Spring season, while Chuanyu 117, Andigena type does best in the Autumn

season (Table 2). Increased plant densities up to 63 plants m-2 reduced the average tuber weight, but in-creased the yield per square meter. The results of this plant density study confirm the trends presented by Tierno et al. (2013). Our yield of tubers per plant were generally much higher than those reported by Tierno et al. (2013). Sequential harvests can promote the removal of dominant tubers which encouraged the development of new tubers situated on lateral stolons of the main

Nutrient Variety Tuber Weight (g m-2) Tuber number per m-2 Tuber number per Plant

spring autumn spring autumn spring autumn

Nutrient Solution I Chuanyu117 1516 c 1971 b 754 d 896 de 14.0 c 16.6 c

Mira 1849 b 1639 c 837 cd 748 e 15.5 c 13.9 c

Nutrient Solution II Chuanyu117 1844 b 2222 a 976 bc 1098 bcd 18.1 b 20.3 bc

Mira 2170 a 1795 bc 1064 ab 1049 cd 19.7 ab 19.4 ab

Nutrient Solution Ⅲ Chuanyu117 1542 c 2020 ab 1189 a 1450 a 22.0 a 26.8 a

Mira 2092 a 1643 c 1223 a 1151 bc 22.6 a 21.3a

Nutrient Solution Ⅳ Chuanyu117 1308 d 1956 b 902 bcd 1287 de 16.7 bc 23.8 ab

Mira 1674 bc 1341 d 983 bc 919 de 18.2 bc 17.0 bc

Table 2. The effect of different nutrient solution on tuber weight and number in aeroponics in spring and autumn

Means followed by the same letter between rows are not significantly different at p<0.05

Figure 4. The effect of different plant densities on tuber production. (a) The number of tubers m -2; (b) Yield m-2; (c) The number of tubers per plant; (d) Yield per plant.

Aeroponics production of seed potato 72

16 plants m-2

26 plants m-2

54 plants m-2

44 plants m-2

63 plants m-2

80 plants m-2

95 plants m-2

16 plants m-2

26 plants m-2

54 plants m-2

44 plants m-2

63 plants m-2

80 plants m-2

95 plants m-2

16 plants m-2

26 plants m-2

54 plants m-2

44 plants m-2

63 plants m-2

80 plants m-2

95 plants m-2

16 plants m-2

26 plants m-2

54 plants m-2

44 plants m-2

63 plants m-2

80 plants m-2

95 plants m-2

stolon and consequently increased the overall yield (Lommen 1995). In this study, sequential harvests increased the mini-tuber number per plant but did not increase the yield per plant. The initiation of the sequential harvests was too late, being started at 90 d after planting. Ideally, harvesting should commence when tubers weigh 3 g regardless of days after planting. Kim et al. (1997) and Farran and Mingo-Castel (2006) found that highest yields were obtained with shorter intervals of 7-10 d. Lommen and Struik (1992) showed distinct advantages from sequential harvests as the larger tubers are no longer the primary sink for photosynthate. Meanwhile, repeated harvesting offers the possibility of obtaining tubers of a desired size (Ritter et al. 2001). The disadvantage of sequential harvests is the different physiological ages of the harvested tubers when they are replanted. Tubers harvested during the first harvest sprout earlier while the ones harvested last would sprout later. Irregular emergence after planting will potentially reduce final yield although this irregularity could be partially corrected by storing the different harvested tubers at varying temperatures, followed by a diffused light storage. The results of these experiments proved to be extremely valuable in assisting the commercial

aeroponic sector in Sichuan to apply the best available technology to produce pre basic seed tubers. On an area basis, the productivity of producing seed tubers is efficient with well over 1,200 tubers m-2. The advantages of using a soilless media avoids the risk of soil borne diseases, creating a high demand for these seed potatoes.

ACKNOWLEDGEMENT The World Bank and the International Potato Center provided the funds and expertise to initiate this work after the severe Earthquake in May 2008, under a project to help replenish the seed potato supply of the farmers who lost everything but their lives

REFERENCES Chang DC, Cho IC, Suh JT, Kim SJ, Lee YB. 2011.

Growth and yield response of three aeroponi-cally grown potato cultivars (Solanum tu-berosum L.) to different electrical conductivi-ties of nutrient solution. Am J Potato Res. 88: 450-458.

Chiipanthenga M, Maliro M, Demo P,Njoloma J. 2012.

Potential of aeroponics system in the produc-tion of quality potato (Solanumtuberosum L.) seed in developing countries. Afr J Biotechnol 11: 3993-3999.

Demagante AL,Vander Zaag P. 1988. The response of

potato (Solanum spp.) to photoperiod and light Intensity under high temperatures. Pota-to Res. 31: 73-83.

Farran I, Mingo-Castel AM. 2006. Potato minituber

production using aeroponics: Effect of plant density and harvesting intervals. Am J Potato Res. 83: 47-53.

He W, Hu JJ, Wang KX,Tang M. 2008. Production,

technology and development of virus-free seed potato in China. Southwest China Jour-nal of Agricultural Sciences. 21: 187-189.

He W, Xie KY, Vander Zaag P. 2014. Experience with

aeroponics for pre- basic seed potato production in Sichuan China. Am J Potato Res. 91: 49.

Figure 5. The effect of misting frequency on tuber production (a)Yield per plant; (b) Average number of tubers per plant. Treatment 1, misting 30 sec per 10 min; Treatment 2, misting 30 sec per 20 min.

TN/P First harvest Second harvest Third harvest Total

Cultivar A B A B A B A B

Chuanyu117 0 2.9 a 0 3.5 a 0 27.4 a 29.3 a 33.8 a

Mira 0 2.5 a 0 3.8 a 0 16.6 b 19.5 b 22.9 b

LSD (0.05) - ns - Ns - 5.9 5 5.6

Y/P

Chuanyu 117 0 9.9 a 0 10.4 a 0 33.6 a 54.0 a 53.8 a

Mira 0 10.2 a 0 7.5 a 0 15.7 b 31.4 b 33.4 b

LSD (0.05) - ns - ns - 3.4 4.1 12.1

Table 3. Tubers per plant harvested with one final harvest (A) or 3 sequential harvests (B)

TN/P: Numbers of tubers per plant, Y/P: Yield per plant (g). A: One-time harvest, B: Several harvest; Means followed by the same letter between rows are not significantly different at p<0.05

73 K Wang et al.

Kim KT, Kim SB, Ko SB, Park YB. 1997. Effects of minituber picking intervals on the yield and tuber weight of potato grown in aeroponics. RDA J Horticult Sci. 39: 65-69.

Levy D, Veilleux RE. 2007. Adaptation of potato to

high temperatures and salinity-a review. Am J Potato Res. 84: 487-506.

Lommen WJM. 1995. Basic studies on the production

and performance of potato minitubers. [MS Thesis, No. 1912]. Wageningen: Wageningen University.181 p.

Lommen WJM, Struik PC. 1992. Production of potato

minitubers by repeated harvesting: Effects of crop husbandry on yield parameters. Potato Res. 35: 419-432.

Mateus-Rodriguez JR, De Haan S, Andrade-Piedra

JL, Maldonado L, Hareau G, Barker I, Chuquillanqui C, Otazú V, Frisancho R, Bastos C, Pereira AS, Medeiros CA, Montesdeoca F, Benítez J. 2013. Technical and economic analysis of aeroponics and other systems for potato mini-tuber production in Latin America. Am J Potato Res. 90: 357-368.

Menzel CM. 1980. Tuberization in potato at high

temperatures: Responses to gibberellin and growth inhibitors. Ann Bot. 46: 259-265.

Murashige T, Schoog F. 1962. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiol Plant. 15: 473-497.

Oraby H, Lachance A, Desjardins Y. 2015. A low

nutrient solution temperature and the application of stress treatments increase potato mini-tubers production in an aeroponic system. Am J Potato Res. 92: 387-397.

Otazú V. 2010. Manual de producción de semilla de

papa de calidadusandoaeroponía. Lima (Peru):CIP. 44 p.

Ritter E, Angulo B, Riga P, Herran C, Relloso J, San

Jose M. 2001. Comparison of hydroponic and aeroponic cultivation systems for the production of potato minitubers. Potato Res. 44: 127-135.

Tierno R, Carrasco A, Ritter E and Ruiz De Galarreta

JI. 2013. Differential growth response and minituber production of three potato cultivars under aeroponics and greenhouse bed culture. Am J Potato Res. 91: 346-353.

Vreugdenhil D, Struik PC. 1989. An integrated view of

the hormonal regulation of tuber formation in potato (Solanum tuberosum). Physiol Plant. 75: 523-531.

Aeroponics production of seed potato 74