Genotypic and pathogenic variation of Colletotrichum gloeosporioides f.sp. malvae.

Abstract Colletotrichum gloeosporioides f. sp. malvae (C.g. malvae) is pathogenic on velvetleaf (Abutilon theophrasti) but does not cause sufficient damage or mortality to be considered as a biological control agent for this weed. Velvetleaf control might be increased if isolates of C.g. malvae with greater pathogenicity could be identified. C.g. malvae isolates from Saskatchewan, Manitoba, and Ontario (Canada) were examined to determine their genotypic and pathogenic variation. The random amplified polymorphic DNA (RAPD) technique was used to determine differences among isolates based on the presence or absence of amplified DNA fragments. Isolates were also tested for variation in pathogenicity by stem injection of the pathogen into velvetleaf plants under controlled conditions. All isolates of C.g. malvae were highly pathogenic on velvetleaf. Differences in RAPD patterns were not obtained among C.g. malvae isolates. However, differences in RAPD patterns could be used to differentiate isolates of C.g. ma...