Effect of Gibberellin (GA3) and Urea on Hybrid Rice Seed Production

Abstract

The research on effects of gibberellin (GA3) and urea on hybrid rice seed production wee conducted at chai Nat Rice Experiment Station (CNT) during 1994-95 wet season (WT). R line : sprlr75055-325-2-1 was seeded three times with 6 day-interval. A line : CNTA-10 (or RD21A-10) was seeded at the second seeding date of R line and transplanted on the same day as R line at 25 days old seedling. The ratio on R line to A line was 3:6. The first, second and third seeding of R line were transplanted alternately along the rows at the spacing of 20x20 cm. The experimental design was RCB with 4 replications and 6 treatments; 1) control, 2) 20 ppm GA3, 3) 40 ppm GA3 4) 60 ppm GA3. 5) 60 and 30 ppm GA3 at interval of two days and 6) 1.5% urea. GA3 and urea were sprayed at 15-20% heading after flag leaf clipping when the tillers started heading. The results of 1994 study showed that GA3 increased only plant height. Both GA3 and urea did not affect panicle exsertion, panicle number/hill, % seed set, 100 grain weight and grain yield. Seed setting of all six treatments were not significantly different at P = 0.05. In 1995 the 1.5% urea gave the highest seed set (17.55%) but was not significantly different from the control (15.25%). The application of GA3 and urea did not affect the percentage of seed set. This study indicated that no need to apply neither GA3 nor 1.5% urea for producing F1 hybrid seeds, only leaf clipping and supplementary pollination during peak anthesis period for one week enough.