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

Abstract

ABSTRACTBlast is a devastating disease of rice caused by the fungusPyricularia 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 ofP. oryzaepopulations from both hosts. Cross infectivity ofP. oryzaeisolates 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. oryzaeisolates from wild rice were pathogenic to cultivated rice but, on average, had a narrower range of cultivar compatibility. Results of pathogenicity tests suggest thatP. oryzaeisolates from wild rice have the potential to attack cultivated rice in the field. However, populations ofP. oryzaeon 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.