Poster Session: Disease Control and Pest Management - Chemical Control

205-P

Predominance of resistance to QoI fungicides in populations of the wheat blast pathogen Magnaporthe oryzae from Brazil.
V. L. CASTROAGUDIN (1), J. T. A. Reges (2), S. C. Oliveira (3), J. L. N. Maciel (4), B. A. McDonald (5), P. C. Ceresini (6)
(1) UNESP Univ Estadual Paulista. CNPq 504073/2011-7., Ilha Solteira, Brazil; (2) UNESP Univ Estadual Paulista., Ilha Solteira, Brazil; (3) UNESP Univ Estadual Paulista. FAPESP 2013/03116-0., Ilha Solteira, Brazil; (4) EMBRAPA Wheat / Trigo, Passo Fundo, RS, Brazil; (5) ETH Zurich, Zurich, Switzerland; (6) UNESP Univ Estadual Paulista. FAPESP 2013/10655-4. CNPq 307361/2012-8., Ilha Solteira, Brazil

Wheat blast caused by Magnaporthe oryzae is a threat to wheat cultivation across central-southern Brazil. Its control relies strongly on strobilurin fungicides (Quinone oxidase inhibitors, QoI). Resistance to QoI (QoI-R) has been reported for several pathosystems worldwide. Here, we report the occurrence and distribution of QoI-R in populations of M. oryzae from Brazilian wheat fields (N = 316, of which 189 derived from wheat and 91 from weed species within fields sampled in 2012, and 36 from wheat sampled in 2005). Sequencing of cytochrome B gene (cytB) distinguished nine haplotypes, four of which contained the G143A mutation linked to QoI-R. While the haplotype H1 (resistant to QoI) predominated (71% of the isolates), the haplotype H9 (sensitive to QoI) was in 20% of the isolates. The other seven haplotypes were detected only in weeds isolates. While 92% of the wheat-derived isolates and 48% of the 2012 weed-derived had the G143A substitution, only 32% of the 2005 isolates showed this mutation. The QoI-R isolates represented distinct multilocus SSR genotypes, indicating multiple origins. Phenotypic data from in vitro assays (based on sensitivity to azoxystrobin at 10 ppm) fully supported the cytB data. This is the first report of the occurrence and widespread distribution of the cytB allele conferring QoI-R in populations of the wheat blast pathogen. These findings point out the need to reexamine the use of strobilurins for managing wheat blast in Brazil.