Fitness of Monilinia fructicola isolates with different levels of sensitivity to azoxystrobin

Isolates of Monilinia fructicola with reduced sensitivity to azoxystrobin have been reported in the main Brazilian peach-growing regions. Thus, studies quantifying fitness of M. fructicola isolates with different levels of sensitivity was studied to improve anti-resistance strategies. Mycelial growth rate and colony sporulation were determined in vitro, and monocyclic components (disease incidence, lesion diameter, lesion sporulation, incubation and latent periods) were evaluated on peaches for each isolate individually. For the ex vivo experiments, multivariate analysis were carried out. Mycelial growth rate in vitro ranged from 0.27 to 0.90 cm day^‑1 and spore production in vitro from 0.4 to 4.4×10² conidia mL^‑1 for the different M. fructicola isolates. In peaches, the incubation period varied from 2.5 to 13 days, the latent period varied from 5 to 13 days, disease incidence varied from 50.8 to 90%, lesion diameter varied from 3.5 to 8 cm and spore production varied from 58.6 to 308.1 conidia mm^‑2. According to multivariate analysis, which takes into account the effects of all monocyclic components, isolates with reduced sensitivity to azoxystrobin had similar fitness as highly sensitive isolates. Multivariate analysis is a powerful tool to evaluate pathogenic fitness of isolates.