Genetic bases of instability of male sterility and fertility reversibility in photoperiod-sensitive genic male-sterile rice.

Photoperiod-sensitive genetic male-sterile (PSGMS) rice, with its male fertility regulated by photoperiod length, is very useful for hybrid rice development. However, breeding for new PSGMS lines has faced two major difficulties - the stability of male sterility and the reversibility of male fertility. In this study we assessed the genetic bases of stability of sterility and fertility reversibility using a molecular marker-based approach. A cross was made between two newly bred PSGMS lines: Peiai 64S, which has a stable sterility but is difficult to reverse to fertility, and 8902S, which has a unstable sterility but is easy to reverse to fertility. The fertility of the parents and of the F(1) and F(2) populations was repeatedly examined under 11 different long-day and short-day conditions. The genetic effects were assayed by interval mapping and two-way analyses of variance using the F(2) data of 128 polymorphic loci representing all the 12 rice chromosomes. The analyses resolved a number of single-locus QTLs and two-locus interactions under both long-day and short day conditions. The interactions involved a large number of loci, most of which were not detectable on a single-locus basis. The results showed that the genetic bases of both stability of sterility and reversibility of fertility are the joint effects of the additive effects of the QTLs and additive-by-additive components of two-locus interactions. The implications of these findings in hybrid rice development are also discussed.