Molecular Identification of Podosphaera xanthii and the Susceptibility of Vigna Species Genotypes to Natural Infection of Powdery Mildew

Powdery mildew was observed on 20 genotypes of Vigna unguiculata subsp. sesquipedalis (yardlong beans) and 33 genotypes of V. radiata (mungbean) in Los Baños, Laguna, Philippines. Powdery mildew was collected and then subjected to molecular characterization to identify the species associated with the disease. Based on combined microscopic observations and molecular identification, the species causing powdery mildew to yardlong bean and mungbean was Podosphaera xanthii (Castagne) U. Braun & S. Takam. 2000 (Bas.: Erysiphe xanthii 1845). None of the yardlong beans and mungbean genotypes were resistant to powdery mildew, with disease incidence reaching up to 100% and with fungal colonies present on plant vines and both sides of leaves. This is the first report of powdery mildew disease caused by P. xanthii on yardlong bean and mungbean in the country. Both legume plant species are important food crops in the Philippines. The information from this study will be valuable in formulating other disease management approaches. The lack of resistant plants warrants further screening in legume germplasm collection to identify sources of resistance or tolerance.