Abstract:
Powdery mildew of pea (Pisum sativum) is an important disease in the field
and in the greenhouse. The most widely documented powdery mildew on pea
is Erysiphe pisi, but E. trifolii and E. baeumleri have also been reported. From
greenhouse-grown peas, we obtained powdery mildew samples with rDNA
ITS sequences nearly identical to previously deposited sequences of E. trifolii.
Because detailed studies on host range of this pea powdery mildew in the US
Pacific Northwest were lacking, we tested common legume plants from the
region as potential alternative hosts. Eleven species were used in greenhouse
cross inoculation studies: Lens culinaris, Glycine max, Melilotus albus, M.
officinalis, Medicago polymorpha, M. lupulina, M. scutellata, Lathyrus
latifolius, Trifolium pratense, Vicia cracca, and V. faba. Except for Glycine
max, all the plant species tested developed powdery mildew lesions in 10?14
days after inoculation. Susceptibilities of two of these species (L. culinaris
and M. albus) were also confirmed with detached leaf assays. Results showed
that all the above legumes (except soybean) are potential alternative hosts for
the E. trifolii found on pea. Powdery mildews found on wild legumes
(Meliotus albus and Medicago lupulina) were also confirmed to be E. trifolii,
suggesting that the wild legumes could be inoculum sources of powdery
mildew on greenhouse pea plants during winter months. These findings have
implications in managing powdery mildew of pea.