Competence of roots for race-specific resistance and the induction of acquired resistance against Magnaporthe oryzae

Generally, Magnaporthe oryzae , the causal agent of rice blast disease, is considered to be a typical leaf-infecting plant pathogenic fungus. However, it was recently reported that M. oryzae shares many characteristics in common with root-infecting pathogens and indeed was able to infect roots. Here, we report on studies testing for the capacity of roots of rice and barley to resist infections with M. oryzae . We established that roots of rice plants were colonized by M. oryzae in a manner which is different from the gene-for-gene specificity seen in leaves for the same genotypes. Furthermore, treatment of rice seedlings with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), a chemical that protects leaves effectively against blast by conditioning acquired resistance, was not able to prevent colonization of roots by M. oryzae although a reduction in disease levels was observed. Moreover, BTH was not able to protect barley roots against infection with M. oryzae . Taken together, our results suggest that although roots show intrinsic variation in their ability to resist colonization by M. oryzae , neither gene-for-gene incompatibility nor aquired resistance are as effective at blocking the pathogen as they are in leaves.