A leaf and twig disease of English holly caused by Phytophthora ilicis N. sp.

Publication Type:

Journal Article


Phytopathology, Volume 47, p.95-101 (1957)


This is an expanded account from Oregon State College, Corvallis, of a disease of holly caused by Phytophthora sp. [34, p. 328], for which the name P. ilicis n.sp. is proposed. It was shown that the defoliation which accompanies the disease is due to the production of ethylene by infected leaf tissue. The disease develops from October to May, and is inactive in the summer. The pathogen is distinguishable from P. porri by its smaller oogonia, and from P. hibernalis and P. syringae by the consistent presence of amphigynous antheridia. On diseased holly tissues the sporangia have a shallow apical thickening and no papilla, and measure 18 to 30 by 30 to 50 (average 24 by 39) µ, with persistent pedicels, 5 to 15 µ long. Oogonia average 21 µ and oospores 18 µ, with a slightly yellow wall; antheridia average 13 by 1µ.