VIEW ARTICLE

Ecology and Epidemiology

Germination of Oospores of Sclerospora sorghi in the Presence of Growing Roots of Host and Nonhost Plants. R. G. Pratt, Assistant Professor, Texas Agricultural Experiment Station, Texas A&M University Agricultural Research and Extension Center, P.O. Box 10607, Corpus Christi, TX 78410, Present address: Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Department of Pant Pathology and Weed Science, Mississippi State University, P.O. Drawer PG, Mississippi State, MS 39762; Phytopathology 68:1606-1613. Accepted for publication 8 June 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1606.

Oospores of Sclerospora sorghi maintained between porous membranes in soil germinated at low frequencies adjacent to growing roots of sorghum, corn, oats, wheat, soybeans, and cotton. Germination occurred at similar frequencies in the presence of roots of sorghum seedlings of cultivars both resistant and susceptible to downy mildew, and also in nontreated field soil, autoclaved soil, and sand. No germination was observed in the absence of plant roots. Germination always resulted in formation of single, broad, coenocytic germ tubes which were seldom branched and elongated up to 1.25 mm prior to autolysis. Germination occurred consistently with oospores stored at 25 C for 8 mo, but not with oospores stored at 4 C; however, when oospores were transferred from 4 C to 25 C, the frequency of germination increased steadily after 2, 4, and 6 wk. Most germination occurred within 3 days after growth of roots adjacent to oospores. In all experiments, numerous instances of “false” germination were observed, due to growth of hyphae of mycoparasitic fungi from within oospore walls. Criteria for distinguishing true and false germination of oospores of S. sorghi are discussed.