Incomplete Rice Panicle Exertion in Cytoplasmic Sterile Lines and the Gibberellic Acid Effect

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Hybrid rice varieties are potentially higher yielding than the best inbred varieties and perform better under adverse conditions of drought and salinity. One of the major impediments for seed production of hybrid rice is incomplete panicle exsertion in the cytoplasmic male sterile lines. The unexserted spikelets which are left inside the flag leaf sheath remain unfertile. This research was focused on studying the related traits as well as analyzing the effect of gibberellic acid on them. Examination of the panicle, peduncle and flag leaf sheath length from two days before heading to five days after heading showed that the peduncle length is the only variable factor in this stage. Investigating peduncle elongation process in A (male sterile) and B (maintainer) lines revealed that peduncle elongation is much slower in A line following heading. Gibberellic acid role on peduncle elongation was confirmed by showing its significant effect on detached peduncles. Gibberellic acid spray had no significant effect on panicle and flag leaf sheath but increased peduncle length. The ultimate peduncle length in A line sprayed with GA3 is almost equal to B line without GA3 spray, carrying all the florets out of the flag leaf sheath. Studying the peduncle elongation pattern in eui-10, an elongated uppermost internode IR64 mutant, showed that peduncle elongation rate is much higher than IR64 such that after heading, the eventual peduncle length is almost doubled. This trait can be employed in breeding programs for hybrid rice to improve the performance of heading in male sterile cultivars.

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