Introduction

Papaya (Carica papaya L.) is an evergreen herbaceous commercial fruit crop of tropical and subtropical regions. It belongs to the family Caricaceae. Papaya is best suited in tropical climatic condition with assured irrigation facilities. The mature fruits are available for harvesting after 150-160 days of flowering, and fruits remain available for four to five months. It yields 70 to 80 mt fruits per hectare under proper management. Further, Red Lady is early, vigorous, productive, and tolerant to papaya ring spot virus (PRSV). Micronutrients can tremendously boost crop growth and yield. Foliar application of micronutrients has gained importance in recent years because the nutrients are sprayed directly to leaves and can be made available to the plants at proper time when needed. Zinc and Boron occupy an important place due to its ability to positively influence plant growth and development which imparts resistance to biotic and abiotic stresses (Cakmak, 2008). Boron is a constituent of cell membrane and is essential for cell division. It acts as a regulator of potassium/calcium ratio in the plant and helps in nitrogen absorption and translocation of sugars in plant. Zinc is the important constituent of several enzymes which regulate various metabolic reactions in the plant and is also essential for auxin and protein synthesis (Trivedi et al., 2012). The present investigation was carried out to find the influence of boron and zinc on growth and yield of papaya fruits.

1 Results

1.1 Vegetative Growth Parameters

The vegetative growth parameters such as plant height, number of leaves, petiole length, leaf area, and stem girth of papaya at 120 days after planting showed significant differences with application of different micronutrients treatments (Table 1). However, the maximum plant height, number of leaves per plant, petiole length, and stem girth were recorded with the application of Borax @ 0.3% + ZnSO₄ @ 0.2% and maximum leaf area was recorded with the application of Borax @ 0.3% + ZnSO₄ @ 0.3% . The treatment control recorded the minimum values for vegetative growth parameters.

Table 1 Effect of foliar spray of boron and zinc on vegetative growth parameters of papaya cv. Red Lady in Chitwan, Nepal, 2016 Note: Means are separated by DMRT and columns represented with same letter (s) are non-significant at 5 % level of significance

1.2 Days for Flowering, Fruit Set, and Days to Harvest

The application of different concentrations of borax and ZnSO₄ in combination through foliar spray has significantly reduced the days for flowering, fruit set, and harvest (Table 2). Application of borax @ 0.3 % and ZnSO4 @ 0.2 % significantly resulted in lesser days for first flowering, fruit set and days to harvest, whereas maximum days to harvest were recorded with control and water spray.

Table 2 Effect of foliar spray of boron and zinc on days for flowering, fruit set and days to harvest of papaya cv. Red Lady in Chitwan, Nepal, 2016 Note: Means are separated by DMRT and columns represented with same letter (s) are non-significant at 5 % level of significance

1.3 Yield Characters

Yield parameters were significantly influenced by application of boron and zinc (Table 3 and Table 4). Application of borax @ 0.3 % along with ZnSO₄ @ 0.2 % significantly resulted in maximum fruit length, fruit girth, fruit weight, number of flowers per plant, number of fruits per plant, fruit yield, and pulp weight. The minimum values for yield parameters were recorded with the treatment control. This might be due to the beneficial effect of zinc and boron directly or indirectly.

Table 3 Effect of foliar spray of boron and zinc on yield parameters of papaya cv. Red Lady in Chitwan, Nepal, 2016 Note: Means are separated by DMRT and columns represented with same letter (s) are non-significant at 5 % level of significance

Table 4 Effect of foliar spray of boron and zinc on yield parameters of papaya cv. Red Lady in Chitwan, Nepal, 2016 Note: Means are separated by DMRT and columns represented with same letter (s) are non-significant at 5 % level of significance

2 Discussion

2.1 Vegetative Growth Parameters

Increment in vegetative growth parameters with all concentrations of boron and zinc in combination as compared to control might be due to involvement of boron and zinc in cell division, cell enlargement, and cell wallAs boron helps in nitrogen absorption and boron helps in formation of chlorophyll in the plants. The higher level/concentration of nitrogen results into higher biomass production and this is reflected by the increment of vegetative parameters as like plant height, leaf number, petiole length, stem girth, and leaf area too. Singh et al. (2002) also reported similar results in papaya with the foliar application of zinc and boron.

2.2 Days for Flowering, Fruit Set, and Days to Harvest

The earlier flowering, fruit set, and harvesting of papaya with the of application of boron and zinc might be due to positive influence of boron and zinc on greater synthesis of metabolites as boron and zinc helps in chlorophyll formation and the increase on leaf area. This results into higher assimilation and greater and early synthesis of metabolites into plants. Similarly, boron helps in early flowering, flower bud formation, and production of indigenous florigenic substances. Furthermore, the supply of boron needed for reproductive growth in many crops is more than that needed for vegetative growth (Mengel and Kirkby, 1982; Marschner, 1986; Hanson, 1991), and the same may be true in papaya. Even boron helps in pollen germination, growth of pollen tube, fertilization, and also involves in glucose metabolism. Zinc helps in translocation of hydrocarbons and their metabolism too. Similar findings were reported by Modi et al. (2012) in papaya cv. MadhuBindu and Singh et al. (2005) in cv. Ranchi with the combined application of boron and zinc through foliar spray.

2.3 Yield Characters

Boron and zinc are involved in fruit setting and fruit retention with consequent improvement on fruit number by their activity. They are also associated with photosynthesis, hormone metabolism, and auxin synthesis which is necessary for flower initiation, fruit set, and fruit growth (Rajkumar et al., 2014).

As boron increases pollen grain germination and pollen tube elongation that consequently leads to higher fruit set and a greater number of fruits per plant (Allah, 2006). This finding agrees with the findings of Kudada and Prasad (2002) in papaya cv. Rajdoot. Similar result of increment in number of fruits per plant with the foliar spray of micronutrients viz., borax and zinc sulphate was also reported by Singh et al. (2010) in papaya cv. Ranchi. Boron and zinc help in higher translocation and accumulation of photosynthates from source to sink of the plant. So, the developing fruits act extremely as an active metabolic sink (Singh et al., 2001). According to Chadda and Singh (1971), ZnSO₄ helps in formation of endogenous auxins and other growth stimulatory compounds. Zinc regulates the cell wall permeability and allows more mobilization of water in fruits. The higher water content in fruits contributed to the greater fruit length, and girth (Wali et al., 2005).

3 Materials and Methods

The field experiment was conducted in the net house at Chanauli, Chitwan from January 2016 to December 2016 following randomized complete block design (RCBD) with three replications. Mulching by black polythene plastic was done and set-up was made spreading the plastic pipes along the row with perforation in the certain spacing for the drip irrigation and fertigation purpose. Healthy, disease free and uniform Red Lady papaya seedlings were planted in the experimental field on 11-01-2016 (2^nd week of January) with a spacing of 2.0 m X 1.80 m. FYM @ 5 Kg per plant were applied in a pit before planting the seedlings. Recommended dose of major nutrients for papaya @ 250:250:500 g NPK per plant per year were applied in 6 splits doses at a 2-month interval through fertigation. Different concentration of zinc (0.1%, 0.2% and 0.3%) and boron (0.1%, 0.2% and 0.3%) were combined and applied through foliar spray of borax and ZnSO₄ in five split doses at 15, 30, 60, 90 and 120 days after planting, respectively. The data were collected on plant height, number of leaves per plant, petiole length, leaf area, stem girth, days for first flowering, days for fruit set, number of flowers per plant, days to harvest, number of fruits per plant, yield (Kg plant and mt/ha), fruit weight, fruit length, fruit girth, and pulp weight. Experimental data were analyzed using GenStat Software of 15^th edition and treatment means were separated using Duncan's Multiple Range Test (DMRT) at 5% level of significance.

4 Conclusion

The combined foliar application of boron and zinc enhanced vegetative growth parameters (plant height, number of leaves, petiole length, leaf area and stem girth), reduced days for flowering, fruit set, and days to harvest and also gave highest result for yield parameters (fruit length, fruit girth, fruit weight; number of flowers per plant, number of fruits per plant, fruit yield and pulp weight) in papaya. So, the foliar application of boron with zinc may increase yield of papaya in Chitwan condition.

Acknowledgement

This work is supported by a grant from Directorate of Research and Extension, Agriculture and Forestry University, Rampur, Chitwan, Nepal. The sincere assistance and guidance of Dr. Giridhari Subedi, Senior Scientist-Nepal Agricultural Research Council (NARC), Khumaltar, Lalitpur is acknowledged with thanks.

References

Alila P., Sanyal D., and Akali S., 2005, Responses of papaya cv. Ranchi to micronutrient application, Horticultural Journal, 18(2): 121-125

Allah A.S.E., 2006, Effect of spraying some macro and micro nutrients on fruit set, yield and fruit quality of Washington navel trees, J. Applied Sci., 22(1): 54-56

Balakrishnan K., 2000, Foliar spray of zinc, iron, boron and magnesium on vegetative growth, yield and quality of guava, Annals of Plant Physiology, 14(2): 151-153

Bhatt A., Mishra N.K., Mishra D.S., and Singh C.P., 2012, Foliar application of Potassium, Calcium, Zinc and Boron enhanced yield, quality and Shelf life of mango, Hort Flora Research Spectrum, 1(4): 300-305

Cakmak I., 2008, Enrichment or cereal grain with zinc: agronomic or genetic biofertification, Pl. & Soil, 302:1-17

https://doi.org/10.1007/s11104-007-9466-3

Chadda K.L., and Singh L., 1971, Effect of varying levels of nitrogen on growth, yield and quality of Thomson and Kandhar grapes, Indian J.Hort., 28:257-263

Ghosh A.S., 2009, Effect of foliar application of micronutrients on retention, yield and quality of fruit in litchi cv. Bombai.Environment and Ecology, 27(1): 89-91

Hanson E.J., 1991, Movement of boron out of tree fruit leaves, Hort. Sci., 26:271- 273

https://doi.org/10.21273/HORTSCI.26.3.271

Hassan A.K., 1995, Effect of foliar sprays with some micronutrients on Washington Navel orange trees, 1. Tree growth and leaf mineral content, Annals of Agricultural Science, Moshtohor, 33(4): 1497-1506

Kavitha M., Kumar N., and Jeyakumar P., 2000, Role of Zinc and Boron on fruit yield and associated characters in papaya cv. Co5. South Indian Horticulture, 48(1/6): 6-10

Kudada N., and Prasad S.M., 2002, Effect of manuring on incidence of papaya ring spot virus and yield attributes of pot grown papaya cv. Rajdoot. J. Res. (BAU), 52(3): 224-227

Marschner H., 1986, Mineral nutrition of higher plants, Academic Press, San Diego, CA.

Mengel K., and Kirkby E.A., 1982, Principles of plant nutrition, Int’1 Potash Instt. Bern, Switzerland

https://doi.org/10.1007/978-94-010-1009-2_1

MoAD, 2013, Statistical Information on Nepalese Agriculture 2012/2013, Government of Nepal, Ministry of Agricultural Development.Singh Durbar, Kathmandu, Nepal

Modi P.K., Varma L.R., Bhalerao P.P., Verma P., and Khade A., 2012, Micronutrient sprays effects on growth, yield and quality of papaya (Carica papaya L.) cv. MadhuBindu, Madras Agricultural Journal, 99(7/9): 500-502

Pant V., and Lavania M.L., 2000, Effect of foliar spray of iron, zinc and boron on growth and yield of papaya (Carica papaya L.), South Ind. Hort., 46(1&2): 5-8

Rajkumar J.P., Tiwari P., and Shant L., 2014, Effect of foliar application of zinc and boron on fruit yield and quality of winter season guava (Psidiumguajava) cv. Pant Prabhat, Annals of Agri-Bio Research, 19(1): 105-108

Sajid M., Abdur-Rab N., and Arif M., 2010, Effect of foliar application of Zn and B on fruit production and physiological disorders in sweet orange cv. Blood Orange, Sarhad J. Agric., Vol. No.3

Sing D.K., Paul P.K., and Ghosh S.K., 2002, Response of papaya to foliar application of boron, zinc and their combination, Deptt. Pomology & Post harvest Technol, Uttar Banga Krishi Viswavidyalaya, Pundibari-736 165, Cooch Behar (West Bengal), India

Singh D.K., Ghosh S.K., Paul P.K., and Suresh C.P., 2010, Effect of different micronutrients on growth, yield and quality of papaya (Carica papaya L.) cv. Ranchi.Acta Horticulture, 851: 351-356

https://doi.org/10.17660/ActaHortic.2010.851.53

Singh D.K., Paul P.K., and Ghosh, S.K., 2005, Response of papaya to foliar application of boron; zinc and their combinations, Research on Crops, 6 (2-6): 27

Singh R., Godara N.R., Singh R., and Dahiya S.S., 2001, Response of foliar application of growth regulators and nutrients in ber (ZizyphusmauritianaL.) cv. Umran, Haryana Journal of Horticultural Sciences, 30: 161-164

Trivedi N., Singh D., Bahadur V., Prasad V.M., and Collis J.P., 2012, Effect of foliar application of zinc and boron on yield and fruit quality of guava (PsidiumgujavaL.), Hort Flora Research Spectrum, 1(3): 281-283

Wali V.K., Kaul R., and Kher R., 2005, Effect of foliar sprays of nitrogen, potassium and zinc on yield and physico-chemical composition of phalsa (Grewiasubinqualis) cv. Purple Round.Haryana Journal of Horticultural Sciences, 34: 56-57