Induction of off-season flowering in Jasmine (Jasminum sambac L.)

Abstract

Jasminum sambac L. is an important commercial loose flower crop cultivated for fresh flowers and for concrete extraction. Due to seasonal flowering nature of jasmine glut during the peak season and scarcity of flowers during off-season is usually observed, which creates fluctuations in the price of the crop. So regulation of flower production according to market needs is very essential in jasmine. It is in this respect that the possibility of using the combination of pruning with plant growth regulators for regulation of flowering in jasmine assumes significance. The study entitled “Induction of off-season flowering in jasmine (Jasminum sambac L.)” was conducted at the Department of Floriculture and Landscape Architecture at the College of Agriculture, Vellanikkara during 2020-21. The objective of the study was to evaluate the effects of growth regulators and pruning on induction of off-season flowering in jasmine (Jasminum sambac L.). The experiment was laid out in RBD (with two factors) in two replications. Pruning is done during three different time of the year viz. during last week of September (P1), last week of October (P2) and last week of November (P3); along with the applications of growth regulators in two levels viz. cycocel (1000 ppm, 1500 ppm), paclobutrazol (200 ppm, 300 ppm), mepiquat chloride (150 ppm, 300 ppm) and GA3 (100 ppm, 150 ppm). Growth parameters such as plant height, plant spread, number of primary branches and number of secondary branches, physiological characters such as specific leaf area, chlorophyll a, chlorophyll b and total chlorophyll content of leaves; flowering and yield parameters like number of flowers buds per cyme, number of cymes per plant, number of flower buds per plant, weight of hundred flower buds, flower yield per plant, length of flower bud, width of flower bud, corolla tube length, corolla tube girth, flower yield per plant during offseason and peak season were observed. Pruning have a significant influence on growth and flowering of jasmine. There was a significant variation with respect to vegetative parameters viz. plant height and plant spread. Pruning during last week of September (P1) was superior in terms of vegetative parameters such as plant height and plant spread throughout the period of study. During June 21, plants pruned during last week of October (P2) were found to be on par with plants pruned during last week of September (P1) in terms of plant height. Influence of pruning on plant spread was only significant during the months of February and March, plants pruned during last week of September (P1) were found to be on par with plants pruned during last week of October (P2). There was no significant influence noticed on physiological parameters when pruning was done at three different time periods. Days to first flower bud initiation was found to be less in plants (17.96) pruned during last week of November (P3). The number of buds per plant was significantly higher in plants pruned during last week of November (P3) during February, March and April months of observation (226.92, 297.67 and 260.31 respectively). The number of buds per plant was found to be on par in plants pruned during last week of September (P1) and plants pruned during last week of November (P3) during the month of February. Plants pruned during last week of September (P1) and plants pruned during last week of November (P3) were on par in terms of flower yield during the month of January (42.79 g and 48.93 g respectively); plants pruned during last week of November (P3) was superior in the months of March and April. During offseason significant yield was found in plants pruned during last week of September (P1) whereas during peak season pruning during last week of November (P3) gave superior results (328.01 g and 116. 13 g respectively). Influence of growth regulators was studied and found significant effect with respect to plant height and number of secondary branches. The treatments G1 (cycocel 1000 ppm), G3 (paclobutrazol 200 ppm), G4 (paclobutrazol 300 ppm), G7 (GA3 100 ppm), G8 (GA3 150 ppm) and G9 (untreated plants) were found to be on par in terms of this parameter. Specific leaf area was significantly higher in untreated plants (G9) (198.86 cm2 / g) whereas chlorophyll content was significant among the treatments G3 (paclobutrazol 200 ppm) and G4 (paclobutrazol 300 ppm)(1.285 mg/ g and 1.273 mg/ g). Days to bud initiation was significantly varied and G1 (cycocel 1000 ppm) and plants treated with G4 (paclobutrazol 300 ppm) were on par (11.01 and 9.01 days respectively). Plants treated with G1 (cycocel 1000 ppm) and G3 (paclobutrazol 200 ppm) were found to be significantly superior in terms of number of cymes per plant (78.79 and 76.30 respectively) and number of buds per plant (324.77 and 283.34 respectively). Weight of 100 flowers was significantly higher in plants treated with G7 (GA3 100 ppm) in January (26.26 g), February (26.16 g) and March (26.33 g) and G8 (GA3 150 ppm) in January (26.38 g), March (26.33 g) and April (26.72 g). In terms of corolla tube length treatment with G1 (cycocel 1000 ppm), G2 (cycocel 1500 ppm), G3 (paclobutrazol 200 ppm), and G8 (GA3 150 ppm) had a positive influence and were on par. Even though no significance was noticed in other quality parameters the application of growth retardants had a positive influence on quality parameters compared to control. In relation to effect of growth regulators on yield parameters, significant effect was noticed for total flower yield, yield during offseason and yield during peak season. G1 (cycocel at 1000 ppm) (56. 55, 59.54, 53.5 and 55.35 g), G3 (paclobutrazol at 200 ppm) (42.13, 48.31, 45.41 and 53.01 g) and G7 (GA3 at 100 ppm) (41.103, 46.5, 51. 66 and 47.3 g) were on par from January to April in terms of total yield per plant. During offseason G1 (cycocel 1000 ppm), G3 (paclobutrazol 200 ppm) and G7 (GA3 100 ppm) gave the superior result (335.42, 320.43 and 292.07 g respectively) whereas during peak season in G1 (cycocel 1000 ppm), G3 (paclobutrazol 200 ppm) and G4 (paclobutrazol 300 ppm) (108.85, 98.41 and 98.96 respectively) were found to exhibit significant yield. Considering the interaction effect of time of pruning and application of growth regulators, parameters like days to bud initiation, number of cymes per plant, number of buds per plant, corolla tube length, total flower yield per plant and flower yield during offseason and peak season showed a significant influence. Treatments P1 x G3 (pruning during last week of September + drenching of paclobutrazol at 200 ppm), P1 x G4 (Pruning during last week of September + drenching of paclobutrazol 300 ppm), P2 x G1 (pruning during last week of October + spraying of cycocel at 1000 ppm), P2 x G2 (Pruning during last week of October + cycocel at 1500 ppm), P2 x G3 (pruning during last week of October + paclobutrazol 200 ppm), P2 x G4 (Pruning during last week of October + paclobutrazol at 300 ppm), P3 x G3 (Pruning during last week of November + paclobutrazol 200 ppm) and P3 x G4 (Pruning during last week of November + paclobutrazol at 300 ppm) were found to be on par (8.66, 11.38, 13.5, 12.16, 8.33, 10.16, 10.16 and 11.5 days respectively) in terms of number of days taken for flower bud initiation. Interaction effect on total flower yield showed that P1 x G1 (pruning during the last week of September + cycocel at 1000 ppm) (77.66 g), P1 x G3 (pruning during the last week of September + paclobutrazol at 200 ppm) (61.95 g), P3 x G7 (pruning during the last week of November + GA3 at 100 ppm) (74.29 g) and P3 x G8 (pruning during the last week of November + GA3 at 150 ppm) (82.50 g) gave the significant result. In terms of yield during offseason interaction effect of P1 x G1 (pruning during the last week of September + cycocel at 1000 ppm) gave a higher yield (572. 57 g) when compared with other treatment combinations. P3 x G8 (pruning during the last week of November + GA3 at 100 ppm) (162.57 g) and P3 x G7 (pruning during the last week of November + GA3 at 150 ppm) (160. 54 g) were found to be on par during peak season. Considering the overall effect in induction of offseason flowering in jasmine, combination of pruning during last week of September along with the application of cycocel (1000 ppm) or paclobutrazol (200 ppm) gave the best result.