Taxonomic complexity of powdery mildew pathogens found on lentil and pea in the U.S. Pacific Northwest

Abstract

and field production conditions in the U.S. Pacific Northwest was investigated using morphological and molecular characters. Isolates collected from lentil plants grown in the greenhouse or field displayed morphologies in substantial agreement with descriptions of Erysiphe trifolii, but sometimes with more extensively branched chasmothecial appendages resembling those of E. diffusa. ITS sequences of the lentil fungi were identical to each other, and more similar to GenBank accessions of E. trifolii (99.5%) than of E. diffusa (97%). The data suggest there may be more than one Erysiphe species causing lentil powdery mildew. The fungus on field-grown pea plants was determined to be E. pisi. However, powdery mildew samples obtained from greenhouse pea plants were either E. pisi or E. trofolii depending on the time of sampling and greenhouse location. Therefore, the powdery mildews infecting lentil and pea are more diverse than previously assumed. Powdery mildews from black medic (Medicago sp.) and sweet clover (Melilotus sp.) found near the greenhouses exhibited ITS sequences with 99.9 to 100% similarity to isolates from lentil and pea in the greenhouses, and to isolates from lentil from the field. These weedy legumes could be inoculum sources for powdery mildew of lentil and pea in the greenhouses, and serve as alternative hosts for cultivated legumes.