Plant materials and cultivation
The experiment was conducted at Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU, former IPSA) research farm, Bangladesh, during March to September of 2001 and 2002. The tuberous roots of Rangpuri (Cl 3) genotype were used in this study. They were planted in earthen pots (containing a 1:1 mixture of soil and decomposed cowdung) on February 10, 2001 and February 8, 2002, respectively and watered. The tuberous roots began to sprout 20–25 days after potting. The sprouted tuberous roots were transplanted in pits (30×30×30 cm) in the experimental field on March 8, 2001 and March 10, 2002. The spacing between row to row and plant to plant was 2.0 m and 1.5m, respectively. The plants were supported by bamboo sticks. When the plants were about 1 m high they were allowed to climb on rope net hanged vertically up to 2.5 m from the soil surface. Fertilization and other cultivation techniques (intercultural operations) were followed as recommended by Hussain and Rashid (1974).
Experimental design and treatments
The experiment was carried out in a split–split plot design with three replications. The treatments are as follows: Time of application: A day before anthesis, at anthesis and a day after anthesis Different PGR’s: In 2001, auxins (NAA: naphthaleneacetic acid and 2,4–D: 2,4–dichlorophenoxyacetic acid), cytokinins (CPPU: N–(2–chloro–4 pyridyl)–N’ phenyl urea and Fulmet: forchlorfenuron), gibberellin (GA3: gibberellin A3) and auxin transport inhibitors (TIBA: 2, 3, 5–triiodo benzoic acid and MH: maleic hydrazide) were tested. Each PGR of 50 ppm concentration was applied to ten ovaries at the time of anthesis and ovary length and diameter were recorded 5, 10 and 15 days after spray. Only three PGR’s (2,4–D, Fulmet and CPPU) induced parthenocarpic fruit. In 2002, therefore, 2,4–D, Fulmet and CPPU were used. Spraying concentrations: 25, 50 and 100 ppm. The concentrations in molar form for 2,4–D are respectively101, 202 and 404 µM and for CPPU or Fulmet are 113, 226 and 452 µM, respectively. Time of spraying was arranged in the main plot (main plots contain 27 plants per replication i.e. three plants/concentration/PGR in a replication, 3–5 first flashed flowers were sprayed in each plant), and different PGR’s (9 plants/replication) and spraying concentrations (3 plants/replication) were applied to sub plot and sub–sub plot, respectively. The 2,4–D was dissolved in ethanol while CPPU was dissolved in 1% DMSO (Dimethyl sulfoxide) to make stock solution. Ten to fifteen ovaries in three plants selected randomly at first fruiting stage were treated (0.5ml per ovary) in each treatment with three replicates. All the treated flowers were bagged in the afternoon one day before anthesis, re–bagged after application and kept bagging up to 3–4 days to prevent from open pollination.
Data collection and analysis
Fruit set percent, length, diameter and weight of fruit were recorded 5, 10 and 15 days after spraying. The mean data of 10–15 ovaries for each treatment were analyzed using standard statistical procedure of ANOVA and Duncan’s Multiple Range Test (DMRT) to compare means of treatments and their interactions.