The experiment was conducted at the Plant Physiology field of HRC, BARI, Gazipur during two consecutive summer seasons of 2015 and 2016.The variety ‘BARI Lau-4’ was used in this experiment. The experiment consisted of eight treatments viz., T0 = control (distilled water), T1 = GA3 @ 10 ppm, T2 = GA3 @ 30 ppm, T3 = NAA @ 100 ppm , T4 = NAA @ 150 ppm, T5 = MH @ 50 ppm, T6 = MH @ 150 ppm and T7 = CCC @ 500 ppm. The sources of GA3 and CCC were Isha, Chemical Pvt. Ltd. (India), and those of MH and NAA were BDH Chemicals Ltd. (England) and SD Fine Chemicals Ltd. (Mumbai, India), respectively. All chemicals were Laboratory Grade. 250 mg of gibberellic acid was accurately weighed out using sensitive electronic balance and dissolved in a few ml of alcohol (95%). The solution thus prepared was transferred to 250 ml volumetric flask containing distilled water. The volume of the solution was made upto 250 ml to get the 1000 ppm stock solution. NAA stock solution (1000 ppm) was prepared by dissolving 500 mg NAA powder in 500 ml of distilled water. 500 mg NAA powder was accurately weighed out and dissolved by keeping it in a 500 ml volumetric flask and by adding 1 N NaOH solution drop by drop till the powder was completely dissolved. The volume was adjusted to 500 ml with distilled water in a volumetric flask. Thus the stock solution was prepared. 500 mg MH was accurately weighed out using sensitive electronic balance and dissolved in a few ml of 1 N NaOH. 100 ml of distilled water was added in a 500 ml volumetric flask. The solution was then adjusted to 500 ml by adding distilled water. This gives 1000 ppm stock solution. 2 ml (50% ai) of CCC was taken by 10 ml pipette ans dissolved in distilled water by adding- shaking method. The volume was adjusted to 1000 ml with distilled water in a volumetric flask to obtain a stock solution of 1000 ppm. Finally, the required lower concentrations of GA3 (10 and 30 ppm), NAA (100 and 150 ppm), MH (50 and 150 ppm) and CCC (500 ppm) were prepared from their stock solutions by using the formula: V1 x S1 = V2 x S2; where. S1: concentration of stock solution (1000 ppm) of the desired chemical (GA3, NAA, MH or CCC), V1 = volume of stock solution of desired chemical (what we have to calculate), S2: concentration of desired chemical and V2: amount of solution required for spray treatment-wise. Then calculated amount (V1) of desired chemical was taken from stock solution and poured into a pot of known volume and then required amount of water was added into this pot. Hand sprayer was used for spray of the chemicals.
The experiment was laid out in a randomized complete block design (RCBD) with three replications. For raising seedlings sandy loam soil and well decomposed cowdung were thoroughly mixed in 1:1 ratio and then plastic pots were filled with this mixture. Seeds were placed in plastic pots on 01 March, 2015 and 11 February, 2016. Seeds were soaked in distilled water for 24 hours to facilitate germination. After final land preparation, pits were prepared by spade and size of each pit was 30 cm x 30 cm x 30 cm. One pit was made in the middle of each plot and one seedling was planted in that pit . Plot size was 2.0 m x 1.5 m and 2.0 m x 2.0 m in 2015 and 2016, respectively. Manure and fertilizers were applied as cow dung, N, P, K, S, B and Zn @ 10000, 80, 45, 88, 25, 1.8 and 4.5 kg/ha, respectively (Quamruzzaman et al., 2015). Half of cow dung; full doses of S, Zn and B, and P and K @ 30 kg/ha each were applied during final land preparation. The rest half of cow dung and P and K @ 15 kg/ha was applied as basal in pit. Rest of N and K was applied in 4 equal installments at 20 days interval starting from 20 days after transplanting. Seventeen day- old seedlings were transplanted on 19 March 2015 and 01 March 2016. First spraying of plant growth regulators (PGRs) were done at the 2 true leaf stage on March 23, 2015 and 03 March, 2016. Second spraying of PGRs was done after 4 days of first spray. Control plants were sprayed with distilled water. Trellises made of bamboos and iron nets were used for the support of each plant individually. Plants were allowed to be grown individually and not be allowed to intermingle with other plants grown beside. Weeding and irrigation were done as required. When 1st flower was seen, it was tagged and each male and female flower was tagged separately throughout the growing period, and the number of male and female flowers was counted. Data were recorded on main vine length, number of primary branches/plant, number of leaves/plant, CCI (Chlorophyll Content Index), Fv/Fm (efficiency of photosystem II), days to first male and female flowers, node order of first and female flowers (from the bottom), number of male and female flowers/plant, number of fruits/plant, individual fruit weight, fruit length, fruit circumference and yield/plot. Then plot yield was converted to per hectare yield. Data on CCI (Chlorophyll Content Index) was taken by Chlorophyll Content Meter (Model: CCM-200, Opti-sciences, USA). The leaf discs were previously adapted to the dark for 20 minutes. The fluorescence data (Fv/Fm) were collected at 70 days after sowing within 10.00 am to 12.00 pm. In the first year (2015), the fruit harvest started from 21 May and ended in 18 June; while, in the 2nd year (2016), fruit harvest started from 09 May and ended in 29 June. Each fruit was harvested after twelve days of anthesis. Thus every fruit was harvested by sharp knife 12 days after anthesis. A total of 7 and 8 harvests were required in 2015 and 2016, respectively. Recorded data were statistically analyzed by MSTAT-C and mean separation was done by Tukey’s W test at 5% level of probability.