Fungicide Sensitivity of Colletotrichum Species Causing Bitter Rot of Apple in the Mid-Atlantic U.S.A.

Abstract

Apple growers in the Mid-Atlantic region of the United States have reported increased losses to bitter rot of apple. We tested the hypothesis that this increase is because the Colletotrichum population has developed resistance to commonly used single-mode-of-action (single-MoA) fungicides. We screened 220 Colletotrichum isolates obtained from 38 apple orchards in the Mid-Atlantic region for resistance to 11 fungicides in FRAC (Fungicide Resistance Action Committee) groups 1, 7, 9, 11, 12, and 29. Eleven (5%) of these isolates were resistant to FRAC group 1 with confirmed beta-tubulin E198A mutations, and two (< 1%) were also resistant to FRAC group 11 with confirmed cytochrome-b G143A mutations. Such low frequencies of resistant isolates indicate that fungicide resistance is unlikely to be the cause of any regional increase in bitter rot. A subsample of isolates was subsequently tested in vitro for sensitivity to every single-MoA fungicide registered for apple in the Mid-Atlantic US (22 fungicides; FRAC groups 1, 3, 7, 9, 11, 12, and 29), and thirteen fungicides were tested in field trials. These fungicides varied widely in efficacy both within and between FRAC groups. Comparisons of results from our in vitro tests with results from our field trials and other field trials conducted across the Eastern US suggested that EC₂₅ values (concentrations that reduce growth by 25%) are better predictors of fungicide efficacy in normal field conditions than EC₅₀ values. We present these results as a guideline for choosing single-MoA fungicides for bitter rot control in the Mid-Atlantic US.

Characterization of Alternaria and Colletotrichum Species Associated with Pomegranate (Punica granatum L.) in Maharashtra State of India

“…Since different Alternaria and Colletotrichum species have different sensitivity toward the commercially available and routinely applied fungicides [ 10 , 11 , 12 , 72 , 73 ], the complete and precise knowledge of the species involved in the etiology of heart rot and anthracnose of pomegranate fruits is the first step toward devising effective management strategies aimed at preventing these two major fungal diseases of pomegranate in India.…”

Identification and characterization of Cladosporium species associated with tea plants (Camellia sinensis) in China

“…Three commonly used fungicides were used for sensitivity analyses: chlorothalonil (Haack et al, 2018), pyraclostrobin (Usman et al, 2021) and thiophanate‐methyl (Martin et al, 2021). For C .…”

“…Three commonly used fungicides were used for sensitivity analyses: chlorothalonil (Haack et al, 2018), pyraclostrobin (Usman et al, 2021) and thiophanate-methyl (Martin et al, 2021). For C. tenuissimum YCW977, 50% effective concentration (EC 50 ) values were determined using mycelial growth assays.…”

“…For pyraclostrobin, concentrations of 0.01, 0.1, 1, 5, 10 and 20 μg/mL were used (Usman et al, 2021). For thiophanate-methyl, concentrations of 0.1, 1, 10, 20, 50 and 100 μg/ mL were used (Martin et al, 2021). Radial mycelial growth was measured after 3 days of incubation at 28°C, and the experiment was independently repeated twice with three replicates.…”

Identifying Species of Pathogens Causing Bitter Rot of Apples in Illinois and Efficacy of Fungicides for Managing the Disease

“…The availability of only a few effective fungicides to control Colletotrichum pathogens and the persistent threat of fungicide resistance development in the pathogens make management of bitter rot of apples a difficult task (Dowling et al 2020). Previous studies have reported variability in fungicide efficacy against bitter rot, which is, to a large extent, related to differences in fungicide sensitivity among Colletotrichum species and efficacy among fungicide active ingredients (Chechi et al 2019;Khodadadi et al 2020;Martin et al 2022;Munir et al 2016). Differences in fungicide sensitivity among species from a single geographical location may be inherent or may have emerged because of fungicide selection pressure influenced by the species-specific inoculum frequency and density and the influx of wild-type phenotypes from nearby hosts (Chen et al 2016).…”