Characterisation of an environmentally induced genic male sterile line of indica rice (Oryza sativa spp. Indica)

Environmentally induced genic male sterility has been successfully used in a 2-line system to produce hybrid rice, with the potential to further increase yield. Elite sterile lines need to be developed for a target production environment to successfully use this novel male sterility system. In this study, a new male sterile line, B06S, identified by Jiangxi Agricultural University, China, was characterised for its flowering characteristics, male fertility behaviour, and the inheritance of male sterility. Flowering characteristics were observed in a sterility-inducing season in Nanchang, China. Compared with the typical fertile cultivars Gui99 and Zhongfu906, B06S started flowering at about the same time, had a slightly longer plant flowering duration (18 days) and a similar panicle flowering duration (6 days), and took longer (6 days) to reach 90% flowering spikelets. Also, at the day of peak flowering, B06S started flowering about 2 h earlier and had an earlier peak flowering time (10.00 am), and the percentage of spikelets flowering before noon was slightly lower (83.8%). Spikelet flowering of B06S lasted 5 h, which was more than 2 h longer than the existing sterile lines. Although B06S showed similar openness to other typical sterile lines (PA64S and 595S), it had a higher stigma exsertion rate (82.5%), larger stigma area (0.92 mm(2)), and longer stigma viability ( 4 days). Both pollen and spikelet were completely sterile for more than 75 consecutive days when the environmental temperature was above 24 degrees C, otherwise they would have been fertile. Fertility was slightly influenced by photoperiod. Increased fertility was induced when photoperiod was shorter than 11 h per day. Genetic analysis using the F-2 and BC1 populations of 6 crosses indicated that male sterility of B06S was predominantly controlled by a recessive major gene. B065S can be grown in large quantity in the winter nursery in Hainan Island, China. A number of crosses combinations between B065S and indica cultivars had significantly higher yield than the best widely grown hybrids in Jiangxi and other parts of China with similar climates. The best early maturing (B06S x 458) and late maturing (B06S x Gui99) hybrids had 8.9 and 10.3% higher yield than the best currently used hybrids (Jinyou402 and Jinyiugui99, respectively), and will be released in 2007.