INHERITANCE OF ADULT-PLANT RESISTANCE TO POWDERY MILDEW IN KNOX-62 AND MASSEY WINTER WHEATS

Adult-plant resistance (APR) to powdery mildew [Blumeria graminis (DC.) E. O. Speer f. sp. tritici Pm. Marchal; syn Erysiphe graminis f. sp. tritici] is more durable than hypersensitive major gene resistance, but little is known about the inheritance of this type of resistance. Inheritance of APR was studied in four winter wheat (Triticum aestivum L.) crosses. Parents, F-1, F-2, F-3, and backcross populations were evaluated in the field under natural epidemics of powdery mildew. The number of genes governing APR in 'Massey' and 'Knox 62' wheats was estimated by both qualitative and quantitative methods. Mildew severity was used in the qualitative methods, while area under the disease progress curve was used in quantitative estimates. Results indicate that two to three genes confer APR in these cultivars. Heritability estimates for APR ranged from 0.40 to 0.56 when standard units and F-3/F-2 regression methods were used. The variance components method estimated higher heritabilities which ranged from 0.79 to 0.95. Since APR in these cultivars is governed by few genes and heritability estimates are moderate to high, selection for this resistance in early segregating generations should be effective. Powdery mildew resistance in Knox 62 has been effective during its commercial cultivation over 20 yr. Massey has maintained its APR to powdery mildew since its release in 1981; therefore, APR derived from these cultivars is expected to be durable.