Evaluation of bacterial blight resistance reaction

Bacterial blight (BB) is a critical disease of rice caused by the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) resulting in heavy yield losses. Application of host resistance is the most effective approach to solve this problem. To date, 27 major resistance genes (R genes) have been identified (Table 1) and utilized for breeding of resistant varieties. However, it is highly probable that the resistance of cultivars having only a single major R gene would easily be broken down by the attack of diverse and rapidly evolving pathotypes of pathogenic bacteria (over 30 pathotypes have been reported). To overcome such problems, discovery of new wider-spectrum resistance genes and understanding the physiology of infection and the defense response at the molecular level are the most important and urgent issues. The availability of diverse genetic resources is essential in these studies. IRRI (international Rice Research Institute) performed a large screening of the resistance genes in wild rice germplasm (Heinrichs et al. 1980). As one of the second term activities, we have evaluated the BB resistance reaction among the wild rice accessions collected in the first term NBRP-Rice Resources and are aiming to identify new source of resistance genes.

Table1 Genes conferring resistance to the bacterial blight pathogen Xanthomonas oryzae pv.oryzae.

*1: ND ,not determined.
*2: D,dominant; r,recessive; SD,semidominant.
*3: Oryza sativa cultivar (roman type),or Oryza species(italics).