Population structure and pathogenicity tests of <i>Pyricularia oryzae</i> on wild and cultivated rice in Mali

Abstract Blast is a devastating disease of rice caused by the fungus Pyricularia oryzae . The role of infected straw and seed as sources of primary inoculum in blast disease epidemics is well known. The role of alternative hosts is yet to be confirmed. The current study sought to assess if wild rice is a major source of inoculum for cultivated rice by comparing the genetic structure of P . oryzae populations from both hosts. Two hundred and eighty‐two strains were genotyped with 12 simple‐sequence repeat (SSR) markers. Cross infectivity of 20 P . oryzae isolates was also assessed using pathogenicity tests. Samples were collected from cultivated and wild rice organs with blast symptoms in irrigated and lowland areas of Mali in Koulikoro, Sikasso and Ségou regions. Under controlled conditions, P . oryzae isolates from Oryza longistaminata wild rice were pathogenic to cultivated rice and had a similar range of cultivar compatibility to isolates from cultivated rice. Results of pathogenicity tests suggest that P . oryzae isolates from wild rice ( O . longistaminata and Oryza barthii ) have the potential to attack cultivated rice ( Oryza sativa ) in the field. However, populations of P . oryzae on cultivated and wild rice were genetically differentiated. A very large fraction (94.4%) of the multilocus genotypes identified were specific to one host species or the other. Thus, although physically close, each rice species hosts a different population of the pathogen, and our results support the hypothesis that wild rice is not a major source of blast inoculum for cultivated rice.