Effect of Water Potential on Reproduction and Spore Germination byFusarium roseum'Graminearum,' 'Culmorum,' and 'Avenaceum'

Abstract

Production of macroconidia by isolates of F. roseum ''Graminearum'' (Group I, sensu Francis and Burgess), ''Culmorum'' and ''Avenaceum'' [soil-borne plant pathogens] (all isolated from Washington, [USA]), 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 .apprx. -15 bars. Sporulation by these isolates was nil at .apprx. -80 bars and below for ''Culmorum'' and at -50 to -60 bars and below for ''Graminearum'' and ''Avenaceum''. Production of macroconidia by 2 isolates of ''Graminearum'' from Pennsylvania [USA] (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 .apprx. -15 bars and nil at .apprx. -50 bars and below. Percentage spore germination for all isolates, including conidia, chlamydospores and ascospores, was uniformly maximal at all water potentials .apprx. -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 -60 to -80 bars. The isolates of ''Graminearum'' Group I behaved more like those of ''Culmorum'' than like those of ''Graminearum'' Group II.