Physiologic and Environmental Factors that Affect the Severity of Snow Mold of Wheat. G. W. Bruehl, Professor, Department of Plant Pathology, Washington State University, Pullman 99163; Barry Cunfer, Technical Aide, Department of Plant Pathology, Washington State University, Pullman 99163. Phytopathology 61:792-799. Accepted for publication 5 February 1971. DOI: 10.1094/Phyto-61-792.
Recovery from attack by Typhula idahoensis was strongest from plants with several tillers and weakest from plants with two to four leaves. Whereas early seeding results in the largest plants with the greatest ability to recover, it also results in the production of more sclerotia. Deep seeding did not lessen the effects of mold.
Varieties with some resistance enter winter with greater carbohydrate reserves and utilize carbohydrates at a slower rate than fully susceptible wheats. Fully susceptible wheats remain greener longer in the dark at +1 or 0 C than do more resistant wheats. Typhula idahoensis reproduces as prolifically on resistant as on susceptible wheats.
Typhula idahoensis is the most virulent species at 1.5, 0, and –1.5 C. Poorest wheat recovery occurs after attack at 0 C. Fusarium nivale and T. incarnata are second and third in virulence, respectively, but neither causes mold at –1.5 C. Sclerotinia borealis did not attack the wheat in our experiments.
Sclerotinia borealis grew about twice as fast on agar media when sucrose was used to lower the water potential as when KCl was used, and its growth was fastest at water potentials between about –10 to –30 bars. Typhula idahoensis and T. incarnata were favored by higher water potentials. They were more equally tolerant of salts and sucrose. Fusarium nivale grew best at higher water potentials, but some isolates tended to be quite sensitive to KCl and relatively tolerant to sucrose.