The Host Specialization of Erysiphe Cichoracearum from Zinnia, Phlox and Cucurbits

SUMMARY

1.	A powdery mildew from Zinnia elegans is shown to infect Z. elegans, Z. pauciflora, Z. verticillata, Helianthus annuus, Arctium minus, A. nemorosum, Xanthium chinense, X. spinosiini, X. strumarium, Mikania scandens, Hieracium alpinum, H. prenanthoides, Inula helenium, Carlina acaulis, Lactuca perennis, Cosmos sp., Scorzonera hispanica and Felicia amelloides of the Compositae, Salpiglossis sinuata of the Solanaceae, and Cerinthe major of the Boraginaceae.
2.	A phlox mildew is shown to be restricted to Phlox drummondii and the cultivated perennial phlox, no infection occurring on 34 other species reported as hosts for Erysiphe cichoracearum.
3.	A cucurbit mildew from the vicinity of Ann Arbor, Michigan, is shown to be restricted to the Cucurbitaceae, infection failing to develop on all other species inoculated.
4.	The zinnia, phlox and cucurbit mildews are best recognized as forms of Erysiphe cichoracearum DC. ex Mérat, as recognized by Salmon, distinguished by marked differences in their host specialization.