Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: 11/1/1999
Publication Date: N/A
Interpretive Summary: This is the first report of powdery mildew on a range of Medicago species, many with potential applications to sustainable cropping systems in the United States. As these Medicago species become more commonly utilized in U.S. agriculture this information will be increasingly useful. Since there was resistance to powdery mildew in some species and accessions, selection for resistant types for genetic improvement appears possible.
Technical Abstract: Powdery mildew (Oidium sp.) was observed in plots of USDA Plant Introduction accessions of medic plants grown for seed increase at Riverside, CA from 1995 to 1998. White, diffuse to dense, amphigenous mycelia bearing Oidium conidia appeared on shoots in April each year and remained active until the last plants matured in June. Invaded leaflets became necrotic and dropped prematurely, sometimes leaving a green petiole. However, mildew incidence was low in most plots, and symptomless plants occurred in all species. Conidia were ellipsoid-cylindrical and measured 15 to 17 x 39 to 47 um. A sexual state of the fungus was not observed. Morphological characteristics of the anamorph matched those of Erysiphe pisi. In growth chambers, conidia from medic plants caused severe mildew of garden pea (Pisum sativum L. 'Early Perfection'). Powdery mildew was found to occur in Medicago ciliaris, M. constricta, M. coronata, M. discifomis, M. doliata, M. granadensis, M. intertexta, M. italica, M. lesinsii, M. littoralis, M. lupulina, M. minima, M. murex, M. noeana, M. orbicularis, M. rigidula, M. rotata, M. rugosa, M. scutellata, M. truncatula, and M. turbinata. We believe this is the first report of naturally occurring powdery mildew on these species in the United States.