F1 sterility, one of the most common post-zygotic reproductive barriers, is frequently observed in both inter-specific and intraspecific crosses of rice. Elucidating the genetic and cytological mechanisms of F1 pollen sterility is important to exploit genetic resources and to understand the evolutionary dynamics of post-zygotic reproductive isolation in rice. Here, we report two F1 pollen sterility loci, designated S36 and S25, found in an interspecific cross between O. sativa ssp. japonica (Taichung 65) and O. nivara (IRGC105444), and an intraspecific cross between O. sativa ssp. japonica (Asominori) and ssp. indica (IR24). Genetic analyses revealed that both loci are located on distal end of the short arm of chromosome 12 and that allelic interaction at the heterozygous locus caused the sterility of male gametes carrying the japonica alleles in both cases. Comparison of map positions of S36 and S25 suggested that these two loci might be the same locus. Cytological investigation revealed that abnormality of sterile pollen grains caused by S36 occurred mainly at the late bicellular stage after initiation of starch accumulation. This study would provide the better understanding on the genetic nature and the cytological mechanism of F1 pollen sterility in rice.
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