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.

Leaf senescence is one of the most precisely modulated developmental process and affects various agronomic traits of rice. Anti-senescence rice varieties are important for breeding application. However, little is known about the mechanisms underlying the metabolic regulatory process of leaf senescence in rice. In this study, we performed transcriptomic and metabolomic analyses of the flag leaves in Yuenong Simiao (YN) and YB, two indica rice cultivars that differ in terms of their leaf senescence. We found 8524 genes/204 metabolites were differentially expressed/accumulated in YN at 30 days after flowering (DAF) compared to 0 DAF, and 8799 genes/205 metabolites were differentially expressed in YB at 30 DAF compared to 0 DAF. Integrative analyses showed that a set of genes and metabolites involved in flavonoid pathway were significantly enriched. We identified that relative accumulation of PHENYLALANINE AMMONIA-LYASE (PAL), CINNAMATE 4-HYDROXYLASE (C4H), 4-COUMAROYL-COA LIGASE (4CL), CHALCONE SYNTHASE (CHS) and CHALCONE ISOMERASE (CHI) in YN30/0 was higher than that in YB30/0. Three flavonoid derivatives, including phloretin, luteolin and eriodictyol, showed lower abundances in YB than in YN at 30 DAF. We further revealed a MYB transcription factor, which is encoded by OsR498G0101613100 gene, could suppress the expression of CHI and CHS. Our results suggested a comprehensive analysis of leaf senescence in a view of transcriptome and metabolome and would contribute to exploring the molecular mechanism of leaf senescence in rice.

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Rice quality is one of the main targets of rice breeding and is a complex trait that involves grain appearance, milling, cooking, eating and nutritional quality. For many years, rice breeding has contended with imbalances in rice yield, quality, and disease and lodging resistance. Here, the milling and appearance quality, cooking quality, starch rapid viscosity analyzer (RVA) profile, and nutritional quality of grains of Yuenongsimiao (YNSM), an indica rice variety with high yield, high quality and disease resistance, were determined. YNSM had excellent appearance and quality, with low amylose contents and high gel consistency, and these characteristics exhibited significant correlations with the RVA profile such as hot paste viscosity, cool paste viscosity, setback viscosity, and consistency. Moreover, 5 genes related to length-to-width ratio (LWR) as well as the Wx gene were used to detect the main quality genotype of YNSM. The results showed that YNSM is a semilong-grain rice with a relatively high brown rice rate, milled rice rate and head rice yield and low chalkiness. The results indicated that the LWR and food quality of YNSM might be related to gs3, gw7 and Wxb. This study also reports the quality characteristics of hybrid rice developed using YNSM as a restorer line. The quality characteristics and the genotype for grain quality determined through gene analysis in YNSM may facilitate the breeding of new rice varieties that achieve a balance of grain yield, resistance and quality.

Background: Rice quality is one of the main targets for rice breeding, and is a complex trait involving grain appearance, milling, cooking, eating and nutritional quality. For a long time, rice breeding is facing the imbalance of yield, quality, disease resistance and lodging.Result: Here, the grain quality characters (milling and appearance quality, cooking quality, starch RVA profile, and nutritional quality) of Yuenongsimiao (YNSM), a new indica rice variety with high yield, high quality and disease resistance, were performed. It showed that YNSM has excellent appearance and quality with low amylose content, long gel consistency, and had significant correlation with the HPU, CPV, SB, and CS. Moreover, 5 genes related to grain size (GS3, GS9, GW5, GW7, and GW8) and Wx gene were selected to detect the main quality genotype of YNSM. The results showed YNSM was a middle-long grains with relative high brown rice rate, white rice rate and whole white rice rate, and lower chalkiness. The results indicated the grain size and food quality of YNSM might related to gs3, gw7 and Wxb. This research also reported the quality characters of hybrid rice using YNSM as a restorer lines.Conclusions: The quality characters and genotype of grain quality gene analysis in YNSM may facilitate the breeding of new rice varieties achieving a balance between grain yield, resistance and quality.