Development of wilt in mint in response to infection by two pathotypes of Verticillium dahliae and co-infection by Pratylenchus penetrans

Two isolates of Verticillium dahliae in vegetative compatibility group (VCG ) 2B and one isolate in VCG 4A were tested for aggressiveness on peppermint , Scotch spearmint, and native spearmint alone and in combination with the lesion nematode Pratylenchus penetrans. The VCG 2B isolates were more aggre ssive than the VCG 4A isolate on all three mint species. Severity of wilt w as greatest on peppermint and scotch spearmint with the VCG 2B isolates, an d CFU of V. dahliae recovered from infected stems were greater in Scotch sp earmint when inoculated with V. dahliae and P. penetrans than when inoculat ed with VCG 2B alone. Wilt severities and CFU in peppermint and Scotch spea rmint were not increased when inoculated with VCG 4A and P. penetrans compa red with VCG 4A alone. These data indicate that V dahliae isolates from VCG 2B but not VCG 4A interact synergistically with P. penetrans on Verticilli um isolate-susceptible mints. The resistance to Verticillium isolates in na tive spearmint was not affected by the presence of lesion nematodes.