Faba Bean Gall Pathogen Physoderma viciae: New Primers Reveal Its Puzzling Association with the Field Pea Ascochyta Complex.

Recent morphological and molecular studies confirmed Physoderma viciae, and not Olpidium viciae, to be the causative agent of the devastating Faba Bean Gall (FBG) disease on faba bean (Vicia faba) in Ethiopia and also highlighted its ability to cross-infect with other host genera such as Pisum and Trifolium. In this study, the first pair of specific primer 'Physo 1' and primer pair 'Physo D' are reported from molecular sequences of this pathogen from the conserved LSU (S28) gene. Whereas 'Physo 1' readily detects P. viciae, 'Physo D', clearly separates its identity from the common and confounding presence of Didymella/Phoma spp. The study also reports the presence of the Ascochyta blight pathogen complex, symptomless but almost universal on field pea (Pisum sativum), within faba bean infested by P. viciae. We emphasize historical evidence confirming such unique association in other legumes, such as the subterranean clover (Trifolium subterraneum). This new finding has significant implications for rotations involving different legume crop and/or forage legume genera and possibly provides the first explanation for the widespread occurrence of the field pea Ascochyta blight pathogen complex even in the absence of field pea cropping for many years.