Diversity of Cladobotryum mycophilum isolates associated with cobweb disease of Agaricus bisporus in the south African mushroom industry

Abstract

Cladobotryum species and strain diversity of isolates collected from cobweb symptomatic Agaricus bisporus or infected casing soil were investigated due to increased incidences of the disease in the South African mushroom industry. Samples were collected from mushroom farms located in Gauteng, the Western Cape and KwaZulu Natal Provinces of South Africa. Moreover, cobweb disease isolates from the USA and Ireland were included in the study as reference cultures. Isolates were characterised using culture and conidia morphology and were identified as Cladobotryum mycophilum. The isolates were characterised by rapid colony growth between 48 and 72 h on malt extract agar and potato dextrose agar, all but two isolates (GP-15 and KZN-2) produced the pink colour of aurofurasin. All isolates could infect A. bisporus fruiting bodies with varying degrees of aggressiveness. Isolates were sequenced for their ITS, and BLAST analysis showed highest similarity (99–100%) to several ITS sequences of Hypomyces odoratus/C. mycophilum for 35 of the isolates except for one from Ireland that was identified as H. rosellus/C. dendroides. Phylogenetic analysis of the isolates showed South African cobweb disease of mushrooms to be caused by a wide diversity of strains some of which may have originated from elsewhere in the world.