Lack of scientific literature exists regarding the effects of gibberellic acid (GA3) application timings on various phenological and physiological aspects of seed crop of locally available onion cultivars. Therefore, current study was planned in Vegetable Research Area, University of Agriculture, Faisalabad to optimize the growth stage for GA3 application on seed production in two local onion cultivars (Phulkara and Dark Red) during 2013 and 2014. Application timings of gibberellins at 100 mg/L of H2O were as (G1) control (no spray), (G2) foliar application at 2-3 leaf stage, (G3) foliar application at 6-7 leaf stage, and (G4) foliar application at the time of flowering. Data on average of both years showed that tallest plants (66.15 cm) and maximum number of leaves per plant (84.56) were noted in cv. Phulkara when GA3 was applied at 2-3 leaf stage. Minimum number of days to initiate flowering (47.92) and maximum number of umbels per plant (15.45) were noted with GA3 application at 6-7 leaf stage in Phulkara and Dark Red, respectively. The highest seed yield per umbel (2.94 g) was recorded in cv. Dark Red when GA3 sprayed at 6-7 leaf stage, while GA3 application at the time of flowering in the cv. Phulkara produced seeds with highest seedling vigor index (586.79). Overall, it appears that seed yield and quality characters were promoted by the application of GA3 at different growth stages and could be valuable for seed production of onion.
Keywords: Early flowering; Leaf area; Number of umbels; Onion; Seed yield; Speed of germination.