VEGETATIVE COMPATIBILITY AND VIRULENCE OF THE SPINACH ANTHRACNOSE PATHOGEN, COLLETOTRICHUM-DEMATIUM

We characterized 215 isolates of Colletotrichum dematium collected from spinach in Arkansas, California, New Jersey, Oklahoma, Texas, and Ontario, Canada, for vegetative compatibility (using nitrate-nonutilizing mutants) and lesion type (primary or secondary). Isolates recovered from spinach leaves not previously damaged were identified as primary anthracnose isolates, whereas those recovered from leaves with white rust lesions (caused by Albugo occidentalis) were identified as secondary anthracnose isolates. Conidial size and colony color on acidified lima bean agar were recorded. Thirty-nine isolates representing all vegetative compatibility groups (VCGs), lesion types, and geographic origins were further compared in greenhouse virulence tests on the spinach cultivars Fall Green and Grandstand. Isolates of C. dematium from tomato and onion were also included in the virulence and vegetative compatibility tests. All isolates, regardless of host, geographic origin, VCG, or lesion type, produced slightly curved, hyaline conidia with an average size of 21.5-30.9 X 3.0-3.8 mum. Two VCGs (VCG1 and VCG2) were identified among the 215 spinach isolates examined. Isolates of both VCGs were recovered from Arkansas, New Jersey, and Oklahoma. All isolates from California (32) and Canada (4) belonged to VCG1, whereas all isolates from Texas (22) belonged to VCG2. One tomato and one onion isolate each represented unique VCGs. In general, C. dematium isolates from spinach were more virulent on spinach than the isolates from onion and tomato; thus, the forma specialis designation, C. dematium f. sp. spinaciae, appears warranted. Select isolates of C. d. spinaciae representing each of the two VCGs and lesion types from different geographic areas could not be differentiated on the basis of virulence in greenhouse pathogenicity tests.