Effects of Gibberellic Acid Applied at Different Flowering Stages on Agronomic Traits and Yields of Hybrid Rice Parental Lines

Abstract

Gibberellic acid (GA₃) application in hybrid rice seed production plays a vital role in increasing seed yield; however, improper use of GA₃ may affect diversely the growth of hybrid parental lines. This study aimed to investigate the effects of GA₃ application at different flowering stages on agronomic traits and seed yield of hybrid parental lines. A micro-crossing plot experiment was employed for A line multiplication (HCS^A/HCS^B) under five treatments: applying GA₃ at 0%, 10%, 30% and 50% panicle heading stages and not applying GA₃. The results indicated flag leaf length, number of internodes, length of base internode, spikelets per panicle, total dry biomass of both lines, panicle length of HCS^A line and seed setting rate of HCS^B line were not significantly different among the treatments. However, applying GA₃ at 10% panicle heading to 50% flowering stage significantly increased plant height, length of 1^st, 2^nd, and 3^rd upper internodes, total length of these three upper internodes and panicle exsertion rate of these lines. Interestingly, applying GA₃ at 30% panicle heading stage enhanced A line to produce significantly higher panicle exsertion, stigma exsertion, and seed setting rates, ultimately leading to the highest seed yield of A line, while applying GA₃ at 0% panicle heading stage slightly reduced panicle exsertion rate, and produced lower seed yield of both parental lines. These results suggest that applying GA₃ at 30% panicle heading stage can be an effective method for increasing seed yield of A line. A verification test is necessary to confirm the present results.