P-166 - Functional analysis of effectors involved in virulence enhancement in the wheat blast fungus

Wheat blast first emerged in Brazil in 1985 and spread to neighboring South American countries. In 2012, a highly virulent isolate, B71, was isolated in Bolivia, and strains closely related with B71 were found to have caused the wheat blast outbreaks in Bangladesh in 2016 and Zambia in 2018. To identify novel sources of resistance against wheat blast, we focused on rice varieties. We screened the effectors of the wheat blast isolate Br48, which is highly expressed during infection and absent in rice blast isolates. Among the candidate effectors, eTO1 and eTO5 were identified as avirulence genes of Br48 against resistant rice cultivars. Interestingly, the copy numbers of eTO1 and eTO5 have increased in more recent Triticum isolates. Based on these findings, we hypothesized that eTO1 and eTO5 may contribute to the enhancement of virulence in the wheat blast fungus. To test this hypothesis, we disrupted eTO5 or eTO1 of Br48, and produced Br48ΔeTO5 and Br48ΔeTO1. When they were sprayed on susceptible wheat cultivar Fielder, the infection levels were lower compared with Br48. On the other hand, the virulence of Br48ΔeTO5+eTO5 (Br48ΔeTO5 transformants carrying reintroduced eTO5) on Fielder was equal to or higher than that of Br48. These results suggest that eTO1 and eTO5 are involved in the enhancement of virulence in the wheat blast fungus.