Genetic bases of instability of male sterility and fertility reversibilityin photoperiod-sensitive genic male-sterile rice

Photoperiod-sensitive genetic male-sterile (PSGMS) rice, with its male fert ility regulated by photoperiod length, is very useful for hybrid rice devel opment. However, breeding for new PSGMS lines has faced two major difficult ies - the stability of male sterility and the reversibility of male fertili ty. In this study we assessed the genetic bases of stability of sterility a nd 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 t he 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 a ssayed by interval mapping and two-way analyses of variance using the F-2 d ata of 128 polymorphic loci representing all the 12 rice chromosomes. The a nalyses resolved a number of single-locus QTLs and two-locus interactions u nder both long-day and short day conditions. The interactions involved a la rge number of loci, most of which were not detectable on a single-locus bas is. The results showed that the genetic bases of both stability of sterilit y and reversibility of fertility are the joint effects of the additive effe cts of the QTLs and additive-by-additive components of two-locus interactio ns. The implications of these findings in hybrid rice development are also discussed.