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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.

Additional keywords: Phaseolus vulgaris, Sclerotinia sclerotiorum, survival, epidemiology.