Abstract
Bacterial blight (BB), a serious bacterial disease caused by pathogen Xanthomonas oryzae pv. oryzae (Xoo) affects rice growth and yield. Yunnan Province is regarded as a center of rice diversity in China and indeed the world, and has abundant rice landrace resources, which may offer prospective candidate donors in rice improvement and breeding. In this study, a set of 200 rice landraces were evaluated to determine their resistance to 10 pathogenic Xoo strains resistance by the leaf-clipping method. The results indicated that the tested rice landraces had different resistance levels against different Xoo strains. Multiple comparisons showed that the Xoo strain PXO99 was virulent to the tested rice landraces. Sixty-six rice landraces conferred resistance against at least one Xoo strain. These resistant rice landraces screened were then performed the presence of 14 cloned BB resistance genes by closely linked molecular markers and designed specific primers. The results showed that none of these resistant accessions contained xa13, Xa21, Xa27, and Xa45(t) homologous fragments, while 9, 24, 4, 7, 9, 15, 1, 5, 4 and 27 accessions contained Xa1, Xa2/Xa31(t), Xa14, Xa3/Xa26, Xa4, xa5, Xa7, Xa10, Xa23 and xa25 homologous fragments, respectively. Sequence analysis further revealed that nucleotide variations around functional nucleotide polymorphisms region were observed within these accessions containing the Xa1, Xa2/Xa31(t), Xa14, Xa3/Xa26, Xa4, xa5, Xa10, Xa23 and xa25 homologous fragments. These results along with phenotypic resistance spectrum supported that these accessions carried nine resistance homologous genes. Only one accession (Qishanggu_Wenshan) carried the Xa7 resistance gene. We also found that some resistant rice landraces, especially Xilandigu_Baoshan, and Laoyaling_Lincang without the above resistance genes, which mediated broad spectrum resistance to multiple Xoo strains, were identified as potential sources for breeding rice lines resistance to BB.
Highlights
Rice (Oryza sativa L) is one of the most important domesticated food crops in the worldwide
Multiple comparisons indicated that the average lesion length rate (LLR) of rice landraces inoculated with the PXO99 strain was 0.5, which was significantly higher than other strains (Fig. 1A)
A total of 200 representative rice landraces from different origins had been described as the distinct phenotypic resistance reactions towards 10 Xanthomonas oryzae pv. oryzae (Xoo) strains, of which 66 accessions were screened to confer specific resistance against at least one strain
Summary
Rice (Oryza sativa L) is one of the most important domesticated food crops in the worldwide. Xoo races often make the breakdown of rice resistance by highly pathogenic variability in a short period, which attacks rice by principally depending on diverse effectors secreted through a type III secretion system (T3SS) (Gu et al 2005). Constantly employs its own resistance genes to defend the fierce attacks from variable Xoo races (Ji et al 2018). Plant host resistance, chemical measures and nitrogen management have been employed to control BB caused by Xoo races in rice breeding practice (Sombunjitt et al 2017; Chukwu et al 2019). Breeding new resistant rice cultivars would be an effective, economic and environmental approach to better control BB disease (Deng et al 2018). More researchers are interested in discovering available resistance genes for controlling the disease
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