The use of cytoplasm male sterility (CMS) is crucial for three-line hybrid seed production. Two types of CMS have been discovered from Dongxiang wild rice, namely the wild abortion type CMS (CMS-WA) and the Dongxiang wild type CMS (CMS-DW). In this study, we show the molecular identification of the two types of CMS in Dongxiang wild rice. WA352, which conferred CMS-WA, was not detected in Dongxiang wild rice, implying Dongxiang wild rice does not carry the CMS-WA source. Further analysis of WA352 in DY1A, a CMS-DW line, by PCR amplification and sequencing, revealed two insertion-deletion polymorphisms occurred in CMS-DW compared to WA352 of CMS-WA. It was reported that WA352 was comprised of an unknown origin sequence and partial sequences of three open reading frames (ORFs), orf284, orf224 and orf288. The 42-bp insertion was located between the two segments of orf224 and orf288, which created a new chimeric ORF, orf216. This new ORF was also detected in CMS-HL. Based on the 9-bp deletion in orf284, a specific mitochondrial marker of DW-M1 was developed, which could be used to specifically distinguish the DW-type source. Moreover, semi-quantitative RT-PCR analysis preliminarily suggested that both orf216 and orf284 could be considered as candidates for CMS-DW. These findings present a preliminary understanding of CMS-DW at the molecular level.

In order to understand the yield performance and nitrogen (N) response of hybrid rice under different ecological conditions in southern China, field experiments were conducted in Huaiji County of Guangdong Province, Binyang of Guangxi Zhuang Autonomous Region and Changsha City of Hunan Province, southern China in 2011 and 2012. Two hybrid (Liangyoupeijiu and Y-liangyou 1) and two inbred rice cultivars (Yuxiangyouzhan and Huanghuazhan) were grown under three N treatments (N1, 225 kg ha–1; N2, 112.5–176 kg ha–1; N3, 0 kg ha–1) in each location. Results showed that grain yield was higher in Changsha than in Huaiji and Binyang for both hybrid and inbred cultivars. The higher grain yield in Changsha was attributed to larger panicle size (spikelets per panicle) and higher biomass production. Consistently higher grain yield in hybrid than in inbred cultivars was observed in Changsha but not in Huaiji and Binyang. Higher grain weight and higher biomass production were responsible for the higher grain yield in hybrid than in inbred cultivars in Changsha. The better crop performance of rice (especially hybrid cultivars) in Changsha was associated with its temperature conditions and indigenous soil N. N2 had higher internal N use efficiency, recovery efficiency of applied N, agronomic N use efficiency, and partial factor productivity of applied N than N1 for both hybrid and inbred cultivars, while the difference in grain yield between N1 and N2 was relatively small. Our study suggests that whether hybrid rice can outyield inbred rice to some extent depends on the ecological conditions, and N use efficiency can be increased by using improved nitrogen management such as site-specific N management in both hybrid and inbred rice production.