VIEW ARTICLE

Ecology and Epidemiology

Effect of Water Potential on Reproduction and Spore Germination by Fusarium roseum ‘Graminearum,’ ‘Culmorum,’ and ‘Avenaceum’. Jae-Mo Sung, Research assistant, Department of Plant Pathology, Washington State University, Pullman, WA 99164; R. J. Cook, research plant pathologist, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Pullman, WA 99164. Phytopathology 71:499-504. Accepted for publication 1 October 1980. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-499.

Production of macroconidia by isolates of Fusarium roseum ‘Graminearum’ (Group I, sensu Francis and Burgess), ‘Culmorum,’ and ‘Avenaceum’ (all isolated from Washington state), on either potato-dextrose agar or water agar containing carnation leaf pieces and adjusted to different water potentials with either KCl or NaCl, was consistently maximal at about –15 bars. Sporulation by these isolates was nil at about –80 bars and below for Culmorum and at –50 to –60 bars and below for Graminearum and Avenaceum. In contrast, production of macroconidia by two isolates of Graminearum from Pennsylvania (Group II, sensu Francis and Burgess) was maximal at –1.4 to –3.0 bars (the basal medium without salts) and progressively less as the water potential was dropped to –40 to –50 bars, the lower limit. Group II (Pennsylvania) isolates of Graminearum produced perithecia in culture but Group I (Washington) isolates did not. Perithecial production was maximal at about –15 bars and nil at about –50 bars and below. Percentage spore germination for all isolates, including conidia, chlamydospores, and ascospores, was uniformly maximal at all water potentials between about –1 (the highest tested) and –20 bars, was progressively less as the water potential was lowered below –20 bars, and was prevented in the range of –60 to –80 bars. The isolates of Graminearum Group I behaved more like those of Culmorum than like those of Graminearum Group II.