Standardization of grafting and evalution for growth, yield, quality and stress tolerance in cucumber (Cucumis sativus L.)

Abstract

The study entitled “Standardization of grafting and evaluation for growth, yield, quality and stress tolerance in cucumber (Cucumis sativus L.)” was conducted in the Department of Vegetable Science, College of Agriculture, Vellayani during 2019-2021 in order to identify suitable rootstocks, standardise grafting techniques and evaluate growth and performance of grafts in cucumber. The study also aims to evaluate cucumber grafts for nematode and salinity stress. The study was conducted in three parts. Standardisation of grafting in two cucumber scions using five rootstocks was done in part I and evaluation of the grafted cucumber for growth, yield and quality was attempted in part II. In part III, stress tolerance study was conducted in cucumber grafts. Cucumber scion (KPCH-1 and Heera) and five rootstocks (culinary melon, oriental pickling melon, pumpkin, ash gourd and bottle gourd) were raised in protrays. Separate experiments for each rootstock, were laid out in CRD, and replicated thrice for standardization of grafting. Growth regulators (alar and cycocel) at two different concentrations ie., 20 ppm and 100 ppm were sprayed at second leaf stage for reducing seedling height of rootstocks and then grafted using two methods (hole insertion grafting and one cotyledon grafting). Culinary melon and oriental pickling melon germinated faster (3.83 days) but pumpkin attained graftable size earlier (11.67 days) compared to other rootstocks. Bottle gourd was slower to germinate (5.83 days) but early germinated culinary melon took longer time (15.50 days) to attain graftable size. Alar @ 100 ppm significantly reduced the height of rootstock to 8.10 cm and increased the diameter to 1.29mm in culinary melon. Faster graft union was recorded for one cotyledon grafting with highest success percent in both the scions (7.60 and 7.53 days). Spraying of cycocel @20ppm+ one cotyledon grafting recorded highest success percent when culinary melon was grafted onto both KPCH-1 and Heera scions (57% and 35.33%). Application of alar @ 100ppm not only enhanced the diameter of rootstock (1.2mm) but also decreased the height (7.87cm) of oriental pickling melon. Graft success percent of 39% in KPCH-1+Oriental pickling melon and 60.27% in Heera+Oriental pickling melon was observed in the combination of cycocel 20ppm + one cotyledon grafting. Though alar @ 20ppm improved the diameter of pumpkin rootstock (3.80 mm) and shortened the height of pumpkin rootstock (7.37cm). Significant difference was not observed for days taken for graft union formation in any growth regulator spray. KPCH-1 took lower days (3.80 days) for graft union formation in hole insertion grafting whereas the scion Heera took 4.13 days in one cotyledon grafting. The combination of alar @ 20ppm + one cotyledon grafting recorded higher percent of graft success (83% and 77.33%). Cycocel @ 20ppm reduced plant height (6.90cm) and enhanced diameter (2.03 mm) in ash gourd rootstock. Faster graft union (8.67 and 7.87 days) was recorded for one cotyledon grafting and highest success percent (67.33 and 57.40 %). Growth regulators did not exert any significant effect on days taken for graft union but spraying of alar @ 20ppm resulted in the highest success percent of 69.83 % and 53.50 in the scions KPCH-1 and Heera respectively. Combination of alar @ 20ppm and one cotyledon grafting recorded highest success percent of 71.33 % and 63.67% in ash gourd. The treatment of alar @ 100ppm reduced the height of bottle gourd (12.77cm) and alar @ 20ppm enhanced the diameter of rootstock (4.52mm). Among the grafting methods, faster graft union formation (4.73 and 4.27 days) and higher success percent (78.47 and 77.87%) was observed in hole insertion grafting method. Graft success percent of 82.33% in KPCH-1+bottle gourd and 86.67% in Heera+ bottle gourd was observed in the combination of alar 20ppm + hole insertion grafting. Based on the results of part I, uniform grafts from the graft combination of cycocel @ 20 ppm + one cotyledon grafting in culinary melon, cycocel @ 20 ppm + one cotyledon grafting in oriental pickling melon, alar @ 20ppm + one cotyledon grafting in pumpkin, alar @ 20ppm+ one cotyledon grafting in ash gourd and alar @ 20ppm + hole insertion grafting in bottle gourd were selected and planted in main field along with non grafted control in randomised block design replicated thrice for evaluating growth, yield and quality of grafted cucumber under rain shelter condition. The highest vine length (4.37m) was observed in Heera scion grafted onto bottle gourd rootstock followed by Heera scion grafted onto pumpkin rootstock (4.13m). KPCH-1 grafted on bottle gourd (29.33 days) and culinary melon (31 days) rootstocks showed early female flower initiation. The number of fruits was higher in graft combination of KPCH-1 and bottle gourd (32) followed by parthenocarpic grafts with pumpkin (30.33) and ash gourd (30.33) rootstocks. A greater fruit weight was observed in graft combination of Heera and bottle gourd (7.51kg) followed by Heera grafted onto pumpkin (7.14kg). According to Kruskal Wallis test on organoleptic properties, there is no significant difference in appearance, texture, taste, and flavor of cucumber grafts and non-grafts. The graft combination of KPCH-1 with bottle gourd (1.60) and Heera with bottle gourd (1.78) recorded higher benefit cost ratio over the non-grafted control Heera (1.51) and KPCH-1 (1.42). In part II, the best performing graft from each of the scion was selected and evaluated with the non-grafted control under poly house and open field conditions. KPCH-1 grafted onto bottle gourd was evaluated over the non-grafted control KPCH-1 under poly house using replicated t-test. In fruit yield parameters, grafted combination (7.67kg vine-1) outperformed the check variety KPCH-1 (7.06kg vine-1). Under open field condition, the number of fruits per vine was higher in the graft combination Heera and bottle gourd (26.97 vine-1) over the non-grafted control Heera (24.25 vine-1). Experiment V entitled ‘Evaluation of selected grafts for nematode tolerance in pot culture’ revealed that Heera grafted onto pumpkin had highest vine length (1.31m), shoot fresh weight (34g), shoot dry weight (3.15g), root fresh weight (2.62g) and root dry weight of 1.22g among different graft combinations. Number of root galls was low in case of KPCH-1 with pumpkin, Heera with pumpkin and Heera on Ash gourd graft combinations. Based on number of roots galls, rook knot index was calculated and it showed that the above mentioned graft combinations with lower root galls had root knot index score of 3 ie., Moderately resistant. The graft combination KPCH-1 with pumpkin had higher enzyme activities of peroxidase (2.55), poly phenol oxidase (1.965) and phenyl alanine lyase (11.655) reflecting that nematode resistance. The fruit yield parameters like fruit weight (290g) and yield per plant (4.64kg) were higher in the graft combination of Heera and pumpkin. Number of fruits per plant (19.72) was greater in plants of KPCH-1 grafted with pumpkin. However, these graft combinations were not out performing over the nematicide treated non-grafted control plants. The study ‘Evaluation of selected grafts for salinity tolerance in pot culture’ showed that higher survival rate (75%) and lower defoliation rate (32.14%) was observed in graft combinations with pumpkin as rootstock. The vegetative parameters like vine length (0.68m), shoot dry weight (10.07g), root length (9.10cm) were higher in graft combinations of KPCH-1 and pumpkin whereas root fresh weight (4.47g) and root dry weight (0.51g) was higher in the grafts of Heera and oriental pickling melon. The biochemical and physiological parameters Na-K ratio (0.16), proline (15.01 µg g-1), total chlorophyll (1.22 mg g-1), total phenol (1.66 mg 100 g-1) and membrane stability (68.87%) were higher in the grafts with rootstock pumpkin. It can be concluded that, grafting can be commercialized in protected cultivation of cucumber for parthenocarpic and non-parthenocarpic cultivars. According to this study, the scions, KPCH-1 and Heera performed better with the bottle gourd rootstock for almost all vegetative and fruit yield attributing traits. Therefore, this graft combination can be used in sustainable horticulture with higher yield. Further, KPCH-1 and Heera grafts can be utilized for cultivation under nematode and salinity stress conditions using pumpkin as the rootstock.