Incidence, identification and pathogenicity ofCladobotryum mycophilum, causal agent of cobweb disease onAgaricus bisporusmushroom crops in Spain

Abstract

Between 2008 and 2011, outbreaks of cobweb were observed in commercial white button mushroom (Agaricus bisporus) crops in Castilla-La Mancha (Spain). In the last 3 years, the presence of the disease has notably increased resulting in serious economic losses. Based on morphological and genetic analyses, the casual agent of cobweb was identified as Cladobotryum mycophilum. A. bisporus mushroom crops were surveyed over a 2-year period to estimate the incidence of cobweb. The presence of the disease was detected in 32% of the mushroom crops observed, being of particular concern in autumn (44% of crops infected) and winter (37%). As regards the casing material, the percentage of crops affected by cobweb was 34% in crops using mineral casing and 29% in those cased with a peat-based casing, with no statistical relationship between the casing and the presence of cobweb. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in three peat-based casings (C1, C2 and C3). The effect of cobweb on mushroom productivity was evaluated by comparing mushroom production and the cobweb patches detected in the casing soil. The decrease in total yield of mushrooms attributed to cobweb reached 12.9% with C2, and the crop area colonised by cobweb reached a final percentage of 36% with C3.

Cobweb, a serious pathology in mushroom crops: A review

“…The prevalence of cobweb disease in commercial mushroom crops has been reported to vary between 6.8 and 28% in Indian A. bisporus facilities (Seth & Dar, 1989;Bhatt & Singh, 2002), 33% in Turkey (Bora & Özaktan, 2000) and, up to 32% in Spanish commercial button mushroom crops (Carrasco et al, 2016a). Its occurrence is associated with final flushes and is conditioned by the season (McKay et al, 1999;Adie, 2000;Desrumeaux, 2005).…”

“…The occurrence and severity of cobweb gradually increases from the first to the third flush. Although it may be established at any time during the year, it is of particular concern in autumn and winter (Carrasco et al, 2016a).…”

“…must be evaluated by two independent methods: (1) morphology: screening for aurofusarin and camphor odour producers, registering conidia and phialide size as well as taxonomic characters (Carrasco et al, 2016a); and (2) molecular and phylogenetic analysis. The best approach for complete molecular identification involves implementation of multigene phylogenetic analyses, including sequencing of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA), RNA polymerase subunit I (RPB1), DNA-dependent RNA polymerase subunit II (RPB2) and translation elongation factor (TEF) genes (Tamm & Põldmaa, 2013;Zuo et al, 2016).…”

“…First, small, white circular patches appear on the casing soil or basidiomes. These quickly spread by means of a fine grey-white mycelium that resembles a spider web (Carrasco et al, 2016a). Eventually patches of mycelium start to sporulate, producing masses of dry spores that are easy to release when they are physically disturbed, mainly through watering or picking operations − even air currents from air-conditioning systems are sufficiently strong to mobilize the harmful spores (Adie et al, 2006).…”

“…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.…”