email: hirokazu@kpu.ac.jp

Wheat blast caused by Pyricularia oryzae (syn. Magnaporthe oryzae) pathotype Triticum (MoT) was first observed in Brazil in 1985 and has recently spread to South Asia and Southern Africa, potentially becoming a pandemic disease. Several resistance genes/genomic regions have been identified in wheat against wheat blast, including the 2NS/2AS translocation from Ae. ventricosa, Rmg7, and Rmg8, but the number of reported resistance genes is still limited. Therefore, it is desirable to identify new resistance genes and to breed durable resistant varieties by pyramiding diverse resistance genes. 

We have screened a total of 192 Japanese wheat accessions in the wheat blast precision phenotyping platform (PPP) at Jashore, Bangladesh. From this, we identified four accessions (R1, R2, R3, and R4) that exhibited relatively strong resistance in the field. These four accessions were then subjected to indoor inoculation tests with MoT isolate Br48 carrying AVR-Rmg8 (the avirulence gene corresponding to Rmg8) and Br48∆A8 strain/isolate lacking AVR-Rmg8. Both R3 and R4 lines showed resistance to both the isolates, indicating that they possess a novel resistance gene distinct from Rmg8.

Further segregation analysis of resistance in the F₂ population obtained by crossing R3 or R4 with susceptible accessions revealed that resistance and susceptibility segregated at nearly 3:1. These results suggest that a single dominant gene controls the resistance in these two accessions.

However, the degree of resistance was relatively stronger in R3 than in R4. In addition, these two accessions responded differently to inoculation with MoT isolates from Bangladesh, indicating the presence of different resistance genes in the two accessions.

A genome-wide association study (GWAS) using the field trial data from 192 accessions (three-year average of resistance in each line) detected MTAs above -log10(p)=3.5 on chromosomes 2B, 4B, and 7A. Currently, we are mapping the resistance gene regions using F2:3 populations derived from R3 and R4.

This work was supported by the Ministry of Agriculture, Forestry and Fisheries of Japan in the framework of International Collaboration in Agricultural Research (Development of Techniques for Controlling Wheat Blast Disease) and by MEXT KAKENHI Grant Number JP24K01731. The wheat blast PPP at Jashore was supported by Australian Centre for International Agriculture Research.