Adaptabilidade competitiva de Pyricularia graminis-tritici resistente aos fungicidas QoI e SDHI

Abstract

Quinone-outside Inhibitor (QoI) and Succinate Dehydrogenase Inhibitors (SDHI) fungicides haven’t been effective for management of wheat blast disease, caused by Pyricularia graminis-tritici,in Brazil. The selection for resistance of P. graminis-tritici to QoI and SDHI in Brazil were first reported in 2015 and 2017, respectively. The resistance of P. graminis-tritici to QoI is associated with the G143A point mutation in the cytochrome b (cytb) gene, and resistance to SDHI, associated with mutations at sites of the sdhB, sdhC and or sdhD genes. The effect of mutations in cytb and sdh on the fitness of P. graminis-tritici is unknown. Fitness and competitive ability between P. graminis-triticisensitive (S) and resistant (R) to QoI and SDHI were evaluated. Mycelial growth, conidial production in vitro and in vivo, incubation period and aggressiveness were analyzed as fitness parameters. Competitive ability of isolates R and S was measured by severity in wheat leaf and head inoculated in the R:S mixtures: 100R:0S, 80R:20S, 50R:50S, 20R:80S, 0R:100S and 0:0. Photosynthetic activity and chlorophyll a, b and total were determined in leaves 0, 3 and 7 d after S and R inoculation (dpi). Significant difference was detected between fitness parameters of S and R strains (p<0.05), in which the isolate R showed higher performance in vitro and in vivo, when compared with isolate S. In vivo conidia production were higher in leaves inoculated with 80R:20S, with greater aggressiveness in leaves inoculated with 100R:0S and 80R:20S, and when in head, 100R:0S. Highest conidial germination percentage in leaves were in 100R:0S and 80R:20S when in QoI, and to SDHI, 80R:20S and 50R:50S. Symptomatic leaves 7 dpi of isolate R showed lower photosynthetic activity and chlorophyll a, b and total compared to S. The major outcome of this study was evidence the isolate resistant to QoI and SDHI account for a fitness advantage compared with the sensitive isolate one under tested conditions.