Pre and post stage of infection of Magnaporthe oryzae Oryza in wheat leaves with different resistance levels.

Blast fungus (Magnaporthe oryzae B.C. Couch) is an imminent threat to global food security because it causes serious yield losses in rice (Oryza sativa L.) and wheat (Triticum aestivum L.). The investigation of infection processes in resistant and susceptible varieties, as well as the cellular responses involved in resistance, can help us to better understand the process of interaction of the M. oryzae-Poaceae pathosystems. Thus, the objectives of this study were to evaluate the processes of pre- and post-infection of M. oryzae in leaves of wheat varieties with different levels of resistance. The percentage of germinated conidia, appressorium formed, tissue penetration and colonization, and the reaction of leaf tissue to infection were evaluated. A decrease was observed in the percentage of germinated conidia, appressorium formation, tissue penetration and colonization, especially in the tissues of resistant varieties, in addition to an increase in the plant's response to infection, with cell wall reinforcement, cell death, and autofluorescent cytoplasm aggregation. Nevertheless, our data produced a different temporal perspective regarding the expression of the known types of resistance. We found that, for a single genotype, recognition can start as early as 6 h after inoculation and continue to evolve until very late during the infection cycle, culminating in cell death. The combined and overlapping pre- and post-haustorial resistance mechanisms were sufficient to prevent disease symptoms, with a few punctual lesions observed in one of the resistant varieties (BR 18) and no visible symptoms in the other two (Ônix or BRS229) as opposed to susceptible variety.