Biological characteristics of Monilinia fructicola isolates from stone fruits in eastern West Virginia

Monilinia fructicola, the causal agent of brown rot, was recovered from decayed stone fruits (peach, plum and nectarine) in 11 West Virginia orchards. There was significant variation among these isolates with respect to colony morphology, growth rate, sporulation level, sensitivity to fenbuconazole, vegetative compatibility and virulence. Species identification was confirmed using ITS sequences from the nuclear ribosomal RNA gene. The cultural phenotypes on potato dextrose agar (PDA) ranged from white to dark, melanized colonies. The growth rate of the isolates on PDA ranged from 0.3 to 3.2 mm day(-1) at 4 degrees C, from 2.9 to 7.6 mm day(-1) at 10 degrees C, and from 4.8 to 19 mm day(-1) at 24 degrees C. There was a statistically significant relationship between the growth of the isolates on PDA and their aggressiveness on nectarines at 24 degrees C, especially at higher inoculum concentrations. Sporulation of 3-day-old cultures on peach agar at 24 degrees C varied from profuse to no sporulation, with some isolates sporulating only sparsely after 10 days. The EC50 for fenbuconazole ranged from 0.003 to 0.129 g L-1 and for two reference isolates was 0.020 and 0.016 g L-1. Only a few vegetative compatibility groups were identified among isolates within orchards, reflecting the lack of sexual recombination in this region.