Abstract
Bacterial blight (BB) is an important constraint on achieving a high and stable rice grain yield. An increasing number of BB resistance (R) genes have been identified and cloned to increase the available options for rice disease resistance breeding. However, it is necessary to understand the distribution of R genes in rice varieties for rational distribution and breeding. Here, we genotyped five R genes, i.e. Xa4, Xa7, Xa21, Xa23, and Xa27, in seventy main cultivars from Guangdong Province, South China using the corresponding specific markers. Our results showed that 61 varieties carried Xa4, only three varieties carried Xa27, and Xa7, Xa21, or Xa23 was not detected in all tested varieties. Notably, only 33 varieties exhibited resistance to pathotype IV Xoo strains. These results indicate that Xa4 is no longer suitable for widespread use in rice breeding, although Xa4 is widely present in tested varieties. Remarkably, the strongly virulent BB strains of pathotype IX evolved quickly in southern China, and Xa23 was found to effectively confer resistance against the pathotype IX strains. Subsequently, we successfully bred two novel inbred rice varieties as also being restorer lines and two photoperiod- and thermo-sensitive genic male sterility (P/TGMS) lines using the broad-spectrum resistance gene Xa23 through marker-assisted selection (MAS) combined with phenotypic selection. All of the developed lines and derived hybrids exhibited enhanced resistance to BB with excellent yield performance. Our research may potentially facilitate both of the inbred and hybrid rice disease resistance breeding.
Highlights
Rice is one of the most important staple crops because it feeds nearly half of the global population
We collected seventy main cultivars from Guangdong Province, in the southern China rice region, and identified the distribution of the bacterial blight resistance genes using the corresponding specific markers, including Xa4, Xa7, Xa21, Xa23, and Xa27, which act in a dominant manner with broad-spectrum resistance against Bacterial blight (BB) and have been widely utilized in rice resistance breeding
33 cultivars had moderate resistance or more to pathotype IV Xoo strains, and only two cultivars, namely, Huanglizhan (HLZ) and LHZ had moderate resistance to pathotype IX Xoo strains (Table S1). These results indicated that Xa4 had been widely used in rice breeding for BB resistance in Guangdong but was unable to meet the current requirements for rice disease resistance breeding
Summary
Rice is one of the most important staple crops because it feeds nearly half of the global population. The grain production and quality of rice have to be increased and improved to guarantee global food security due to the rapid growth of the global population, global climate change, and other reasons (Tilman et al, 2001; Qian et al, 2016). Rice grain yield and quality are frequently and severely threatened by devastating diseases caused by multiple pathogens, such as Xanthomonas. Rice Bacterial Blight Resistance Breeding oryzae pv. Previous studies have shown that significant grain yield loss of more than 20% was caused by BB, especially in hybrid rice, and the degree of yield loss was affected by the stage of BB infection (Chukwu et al, 2019). The breeding of resistant rice varieties is advocated as being the most costeffective approach to overcome the major obstacle to achieving optimal yield.
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