Avaliação da sensibilidade de isolados de Alternaria alternata patótipo tangerina a triazóis, estrobilurinas e carboxamida

Abstract

The alternaria brown spot is the disease caused by the pathogen Alternaria alternata pathotype tangerine, that has caused severe damage in tangerine and hybrids is in orchards. In Brazil, reports of the pathogen occurrence have been verified since 2001, and today the pathogen is detected in several fruit-producing states. The objective of this work was to evaluate the sensitivity of thirty isolates from different locations, which were identified as A. alternata through morphological analysis and pathogenicity test. They were evaluated for sensitivity to triazoles (DMI – demethylation inhibitors), strobilurins (QoI – quinone oxidase inhibitors) and carboxamide (SDHI – succinate dehydrogenase enzyme inhibitors), in addition to possible adaptive costs. The isolates show resistance to the fungicides DMI and SDHI, with EC50 values between 4.47 μg mL-1 to 27.22 μg mL-1 (difenoconazole), 7.42 μg mL-1 to 15.53 μg mL-1 (tebuconazole) and 2.68 μg mL-1 to 28.72 μg mL-1 (boscalide). All isolates from Campanha-MG showed resistance to QoI fungicides, being insensitive to both azoxystrobin and pyraclostrobin with EC50 higher than 1600 μg mL-1 and 120 μg mL-1, respectively. No reductions in sporulation of SDHI and DMI resistance phenotypes were observed. The mycelial growth of resistant DMI isolates was reduced and indicate the possibility of adaptive cost. Resistant SDHI isolates showed hypersensitivity to oxidative stress. The occurrence of resistance phenotypes to triazoles, strobilurins and carboxamide fungicides in the sampled areas suggest a selection pressure for resistant individuals.