DNA polymorphism in the stem nematode Ditylenchus dipsaci: development of diagnostic markers for normal and giant races.

DNA polymorphism in the Ditylenchus dipsaci complex was investigated using amplified fragment length polymorphism (AFLP) to determine the relationships among populations growing mainly on Vicia faba and to develop diagnostic markers. Twenty-two populations of D. dipsaci originating from different geographical areas and one population of Ditylenchus myceliophagus were used. AFLP proved to be a powerful method to reveal intraspecific polymorphism even within the giant type. The analysis showed a clear distinction between the giant and normal populations, with genetic distances similar to those observed between normal populations and D. myceliophagus or giant populations and D. myceliophagus, strengthening the hypothesis that these two nematode types could be considered distinct species. Two specific AFLP markers differentiating the two types were converted into sequenced characterized amplified region (SCAR) markers. Used in a multiplex PCR, the SCAR primers proved to be a rapid and efficient tool to identify the giant and the normal types of D. dipsaci.