In vitro sensitivity testing of Cladobotryum mycophilum to carbendazim and prochloraz manganese

Abstract

Limited information of fungicide efficacy on cultivated mushrooms and resistance development potential is available. Minor crop industries in general have a smaller arsenal of protectants to rely on and the likelihood of resistance build-up is of greater concern. This study focused on Cladobotryum mycophilum's sensitivity to carbendazim and prochloraz manganese following recent reports on decreased efficacy of both fungicides. The median effective dose (ED50) values for carbendazim ranged between 0.02 mg/L and 4.31 mg/L with 60% of the South African isolates being moderately resistant. The highest resistance factor for carbendazim was 215. Prochloraz manganese ED50 values varied from 0.00001 mg/L to 0.55 mg/L. A significant difference in mean ED50 values for both fungicides tested was observed. Using cluster analysis, no discrimination of isolates previously exposed and unexposed to prochloraz manganese was observed. A wide range of differences in ED50 values indicated moderate resistance to carbendazim and high sensitivity to prochloraz manganese among isolates under investigation. Discriminant analysis indicated significant differences between clusters contributed by one or a few variables. This study provided evidence that prochloraz manganese remains highly fungitoxic to C. mycophilum. However, prochloraz manganese is to be used in a disease management strategy in combination with strict farm hygiene management strategies to retain product efficacy and ensure crop protection.

Cobweb, a serious pathology in mushroom crops: A review

“…Arnold, is currently the most cited causal agent of cobweb. It has recently been described as parasitizing different edible crops in Africa, Asia and Europe, including Agaricus bisporus, Pleurotus eryngii and Ganoderma lucidum (Back et al, 2010;Chakwiya et al, 2015;Carrasco et al, 2016a;Zuo et al, 2016;Gea et al, 2017). C. mycophilum is also a red pigment producer in vitro (Carrasco et al, 2016a).…”

“…Two DMI fungicides, imazalil (to control green mould disease) and prochloraz-Mn (for cobweb), are licensed for use in Australian mushroom crops. In South Africa, prochloraz-Mn and thiabendazole are the fungicides approved for use in mushroom (Chakwiya et al, 2015). Thiabendazole (MBC-fungicide, FRAC code: 1) can be used in USA mushroom crops, as well as chlorothalonil formulates.…”

“…The continuous usage of a given fungicide frequently contributes to pathogen resistance and, consequently, to undermining the value of the active substances available for cobweb control (Chakwiya et al, 2015).…”

“…As soon as a primary cobweb outbreak is located over the casing or carpophores, it must be treated before sporulation, covering the infected area with thick damp paper to avoid the release of conidia and disease dispersion (Pyck & Grogan, 2015). (Back et al, 2012;Kim et al, 2014;Chakwiya et al, 2015;Carrasco et al, 2016a;Zuo et al, 2016). However, several other species have been reported as causing this pathology in commercial mushroom crops.…”

Effect of five fungicides with different modes of action on cobweb disease (Cladobotryum mycophilum) and mushroom yield

“…Legislation in the USA permits the use of thiabendazole [methyl benzimidazole carbamate (MBC) fungicide] in mushroom crops, as well as chlorothalonil formulations (American Mushroom Institute, ). In South Africa, prochloraz‐Mn and thiabendazole are registered for use on mushrooms (Chakwiya et al ., ). Imazalil and prochloraz‐Mn, both demethylation inhibitor‐fungicides (DMIs), are licensed for use in the control of green mould and cobweb respectively, in Australian mushroom crops (APVMA, ).…”