Proposal for a new international system of differentiating races of blast (Pyricularia oryzae Cavara) by using LTH monogenic lines in rice (Oryza sativa L.).

A new systematic, expandable method that allows easy understanding of the relationships between races and resistance genes is proposed for building up an international standard designation and classification of blast races. Blast races were characterized by reactions to 26 Lijian-xintuan-heigu (LTH) monogenic lines for targeting 23 resistance genes, which were divided into five groups, (1) LTH, IRBLa-A, IRBLsh-S, IRBLb-B, and IRBLt-K59, (2) 3 lines of Pii locus region, (3) 7 lines of Pik region, (4) 4 lines of Piz region, and (5) 7 lines of Pita region. Each group consists of 1 to 3 variety unit(s), which were allocated with 3 differential lines (genes) in each and applied codes, 1, 2, and 4, for compatible reactions of blast isolates, respectively. A blast race is characterized by the sum of codes in combinations of three varieties' reactions in each unit with the Gilmour method. In the case of all compatible reactions to differential lines, the race No., 73-i7-k177-z17-ta733, will be designated. This designation method will contribute diversity research for blast races and rice resistance, and pathological, genetic, and breeding studies of blast disease and rice varieties, to build up the durable protection system for blast disease, through enhancement of communication among pathologists and breeders at the grobal level.