Genotypic and pathogenic variation of Colletotrichum gloeosporioides f. spmalvae

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. Vel vetleaf 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 a nd pathogenic variation. The random amplified polymorphic DNA (RAPD) techni que was used to determine differences among isolates based on the presence or absence of amplified DNA fragments. Isolates were also tested for variat ion in pathogenicity by stem injection of the pathogen into velvetleaf plan ts under controlled conditions. All isolates of C.g. malvae were highly pat hogenic 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. malvae from other species or formae speci ales of Colletotrichum.