Wild and cultivated rice host different populations of the blast fungus, Pyricularia oryzae, in Mali

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. Cross infectivity of 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 Segou regions. Under controlled conditions, P. oryzae isolates from wild rice were pathogenic to cultivated rice but, on average, had a narrower range of cultivar compatibility. Results of pathogenicity tests suggest that P. oryzae isolates from wild rice have the potential to attack cultivated rice in the field. However, populations of P. oryzae on cultivated and wild rice were genetically differentiated. Thus, although physically close, each host plant 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.