Diversidade e caracterização da resistência de isolados de Alternaria alternata patótipo tangerina a estrobilurinas

Abstract

Alternaria alternata tangerine pathotype is the causal agent of citrus brown spot, a disease that affects tangerine and their hybrids causing severe yield losses. First report of the citrus brown spot in Brazil was in 2001 at the Rio de Janeiro state and later occurrences in different citrus producing states. Morphological data, phylogenetic analyses and pathogenicity tests were used to identify seventeen isolates as A. alternata tangerine pathotype. Phylogenetic analyses using endoPG gene sequences were clustered the isolates into three previously described lineages represented by worldwide reference strains. Isolates were originated from different locations in the Brazilian Southeast region and were examined for sensitivity to azoxystrobin and piraclostrobin. Most of isolates were insensitive to azoxystrobin and calculated EC50 was higher than 200 µg mL -1 . On the other hand, EC50 ranged from 0.7831 to 45.7 µg mL -1 in the presence of piraclostrobin. Two isolates were identified carrying the point mutation G143A which confers QoI-fungicides resistance to strains. Resistant genotypes isolates showed lower efficiency for both esporulation and conidia germination compared to sensitive isolates, suggesting that may occurs a fitness cost associated to the point mutation G143A. Laser confocal micrographs revealed that PE15 QoI-sensitive isolate showed high reactive oxygen species production and cell death when exposed to piraclostrobin 100 µg mL -1 . On contrary, PE9 QoI-resistant isolate conidia do not demonstrated cell death or reactive oxygen species accumulation. The QoI-resistant-A. alternata genotypes occurrence suggests that strobilurins applications may be selecting resistant individuals in sampled citrus growing areas.