Ascochyta fabae and A. lentis: Host Specificity, Teleomorphs (Didymella), Hybrid Analysis, and Taxonomic Status.

Abstract

Isolates of Ascochyta fabae from faba bean (Vicia faba) and A. lentis from lentil (Lens culinaris) collected from different countries were used in this study. The Didymella teleomorph (sexual state) of each fungus was induced to develop and mature on inoculated sterile lentil stems. Both fungi were heterothallic, with two mating types, designated MAT1-1 and MAT1-2. When certain isolates of A. fabae and A. lentis were crossed, hybrid pseudothecia developed. Growth, sporulation, colony appearance, morphology, and pathogenicity of the hybrid progeny frequently differed greatly from the parent isolates. Inoculations with single-ascospore progeny from matings among compatible isolates of A. fabae caused disease in faba bean but not in lentil; inoculations with single-ascospore progeny from matings among compatible isolates of A. lentis incited disease in lentil but not in faba bean. Inoculations with single-ascospore progeny from crosses between faba bean and lentil isolates did not induce disease in either host. Asci from crosses between A. fabae and A. lentis mostly contained fewer than eight ascospores that were, on average, larger than those from eight-spored asci. Matings among certain isolates of A. fabae resulted in production of pseudothecia with ascospores considerably larger than is typical for D. fabae. Random amplified polymorphic DNA (RAPD) banding patterns of Ascochyta isolates from faba bean and lentil are clearly different, and banding patterns from hybrid progeny from crosses between A. fabae and A. lentis confirmed hybridity. RAPD markers proved useful in supporting identifications of ascospore isolates from faba bean to known Ascochyta species. Dendrogram analysis indicated similarity between the two fungal species was low. The pathogenicity tests, morphological characteristics, and RAPD markers indicate that A. fabae and A. lentis represent distinct taxa. D. lentis, with its anamorph, A. lentis, is proposed as a new species that is distinct from D. fabae, with its anamorph, A. fabae.