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Succinate dehydrogenase inhibitors (SDHIs) fungicides are used to control Asian soybean rust ( Phakopsora pachyrhizi ), and the Sdh C-I86F mutation is related to pathogen resistance. The objective of this study was to determine whether fitness penalties are associated with SDHI resistance ( Sdh C-I86F mutation) in P. pachyrhizi populations. Moreover, the study investigated whether the Sdh C-I86F mutation remained stable after the fungus propagation both in the absence and presence of fungicide. The populations used in this study presented mutations for all genes analyzed ( Cyp51 , Cytb , and Sdh C), except for a wild-type population (WT Sdh C ) found with no Sdh C-I86F mutation. The frequencies of the Sdh C-I86F mutant populations were stable after 36 generations in the absence of fungicide. However, in the case of the WT Sdh C population, the Sdh C-I86F mutation was further detected after one generation of the fungus in the presence of the SDHI fungicide, according to the results of a detached leaf assay. Three tests were performed to evaluate fitness components and sensitivity to fungicides (half maximal effective concentration). Sdh C-I86F mutant populations were more sensitive to osmotic and oxidative stress than the WT Sdh C population; however, the sensitivity to ultraviolet radiation was similar for both populations. All mutated populations were less sensitive than the WT Sdh C when using SDHI (azoxystrobin + benzovindiflupyr), but more sensitive to mancozeb. The presence of fitness penalties, the mutation stability, and the sensitivity to mancozeb presented by the Sdh C-I86F mutant populations can be relevant to the management of the disease in the field.

Glomerella leaf spot (GLS) and bitter rot (BR) on apples are often caused by Colletotrichum acutatum in Paraná State, Brazil. GLS control is difficult because of its rapid development, with an incubation period of only 2 days under favorable conditions. Therefore, producers use successive fungicide applications every season; however, failure to control GLS has been commonly reported. The objectives of this study were to determine the sensitivity of isolates of the C. acutatum species complex obtained from apple orchards in Brazil to mancozeb, thiophanate-methyl, and azoxystrobin fungicides. Isolates from the different parts of the plant (leaves, flowers, buds, and twigs) and cultivars (Gala and Eva) showed different levels of sensitivity to mancozeb, thiophanate-methyl, and azoxystrobin. For mancozeb, the frequencies of isolates were 25% highly resistant, 50% low-resistance, and 25% sensitive. For thiophanate-methyl, the frequencies of isolates were 72.2% highly resistant, 11.1% resistant, and 16.7% moderately resistant. For azoxystrobin, the frequencies of isolates were 11.1% highly resistant, 5.6% resistant, and 83.3% sensitive. Interestingly, no mutations in the β-tubulin and cytochrome b genes were observed in any of the isolates resistant to thiophanate-methyl and azoxystrobin fungicides.