Evidence for pathotype mixtures on Solanum bulbocastanum in Meloidogyne chitwoodi but not in M. fallax

Variability for pathogenicity on seven Solanum bulbocastanum clones was studied in a collection of isolates of Meloidogyne chitwoodi and M. fallax from a wide range of geographical origins. Four different pathotypes could be distinguished within M. chitwoodi, while no specialisation was found in M. fallax. Meloidogyne chitwoodi isolates from the USA showed the largest variation; those from Europe belonged to one pathotype. In several M. chitwoodi isolates, the occurrence of pathotype mixtures was verified and for the first time reported in automictic Meloidogyne spp. The infrequently formed egg masses in incompatible isolate-plant genotype combinations were not able to reproduce further on various S. bulbocastanum genotypes, suggesting some stability aspects of the resistance. The occurrence of pathotypes and mixtures of pathotypes requires special attention in breeding programmes as well as in disease management.