VIEW ARTICLE

Evaluation of Slow-Mildewing Resistance of Knox Wheat in the Field. Gregory Shaner, Assistant Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907; Phytopathology 63:867-872. Accepted for publication 17 January 1973. DOI: 10.1094/Phyto-63-867.

Because major gene, race-specific, resistance to powdery mildew in wheat is often short-lived, studies were undertaken on more stable types of “adult-plant” resistance. Mildew development was followed in field plots on wheat cultivars which were fully susceptible as seedlings, but which had various levels of adult-plant resistance. During grain filling, mildew severity was substantially lower on ‘Knox’ wheat and three of its progeny than on ‘Vermillion’ or ‘Riley 67’. Infection rates, calculated from logit analyses, were lower on Knox and its progeny than on the two susceptible wheat cultivars. The resistance of Knox and ‘Benhur’ was effective regardless of row spacing or planting date. The resistance of experimental line Purdue 5724B3 was less effective in wheat plantings sown 15 September than in those sown 2 or 4 weeks later. The level of Knox’s resistance, and its stability over the past 20 years, suggest that such resistance would provide practical, stable control of powdery mildew in the soft red winter wheat region of the USA.