VIEW ARTICLE

Influence of Water Potential on Growth and Survival of Whetzelinia sclerotiorum. R. G. Grogan, Departments of Plant Pathology, University of California, Davis, California 95616; G. S. Abawi, KYSAES, Cornell University, Geneva, New York 14456. Phytopathology 65:122-138. Accepted for publication 6 August 1974. DOI: 10.1094/Phyto-65-122.

Ascospore germination of Whetzelinia sclerotiorum was not adversely affected by osmotic potentials (ψ) as low as –56 bars, but was reduced by 71% at –73 bars and completely inhibited at –91 bars. Mycelial growth was progressively stimulated as ψ was decreased from –1 to –14 bars, but growth was reduced at lower ψ values. Optimum growth was reduced 50% at ψ of –37 to –47 bars and was nil after 3 days at –91 bars. However, with longer incubation (2 to 3 weeks), measurable growth occurred even at –100 bars. Sclerotia were produced on agar media with ψ from –1 to –64 bars, but not at –73 bars. Apothecia were produced at 0, but not at –6 bars. Expansion of lesions on bean leaves was progressively increased as ψ in inoculum plug was decreased from –1 to –24 bars, and was not adversely affected until the ψ was reduced below –56 bars. However, lesion development was completely prevented at –91 bars. The different osmotica [KCl, sucrose, and salt mixture (KCl, NaCl, Na₂SO₄)] and different basal media (cornmeal agar or turnip extract agar) which were used produced similar effects at comparable ψ. Survival of ascospores ejected onto coverslips or dried bean blossoms was greater at lower relative humidities. Survival of germinated ascospores was closely correlated with length of incubation period and nutrient level of the incubation media, and was associated with the formation of appressoria and other unidentified resistant structures.