Abstract:

The bacterial blight (BB) of rice is caused by the pathogen Xanthomonas oryzae pv. oryzae (Xoo). BB is one of the most important rice diseases all over the world. The most effective and economical approach for BB control in rice production is using BB-resistant cultivars. The broad-spectrum BB resistance gene Xa23 was originally identified from wild rice species Oryzae rufipogon. Xa23 was introduced into cultivated rice variety JG30 by cross and continuous back-crosses, which resulted in the near-isogenic line CBB23. In our previous studies, Xa23 was mapped on the long arm of rice chromosome 11. In this study, we used CBB23 as Xa23 donor and the elite but BB susceptible restorer lines 9311 and 1826 as recipients to develop BB-resistant restorer lines of hybrid rice. The Xa23-linked EST marker C189 was used to select Xa23 in the segregating populations. Marker-assisted selection (MAS) for Xa23 was performed at the seedling stage of plants and followed by conventional selection for agronomic traits at the adult stage. More than 160 introgression lines that harbored homozygous Xa23 and showed stable agronomic traits were obtained. Twenty-one of the introgression lines were subject to BB disease inoculation at the seedling and booting stages in green house, and results showed that all the tested lines were resistant to the most destructive Xoo strain PXO99(P6) while the recipient parents 9311 and 1826 were highly susceptible at both stages. In addition, we used 5 of the introgression lines as restorer lines to make hybrids by crossing them with 3 sterile lines Pei’ai 64S, Guangzhan 63S and Yuetai A. BB-inoculation tests showed the 15 hybrids were resistant or moderately resistant to PXO99 at the seedling stage and highly resistant at the booting stage. Field trials of 6 selected hybrids showed that yields of the hybrids were equal to or even higher than that of the control super hybrid rice Liangyou Peijiu. The lines C6201, C6271 and C6351 obtained in this study are hopeful of being restorer lines of hybrid rice with great potential for commercialization in the near future. These results clearly suggested that the Xa23-linked marker C189 could be effectively utilized in the BB-resistance breeding programs.

Key words: Rice, Molecular marker-assisted selection (MAS), Rice bacterial blight