Adult-plant resistance to powdery mildew in Knox 62 wheat

Quantitative adult-plant resistance is an alternative for short-lived single major-gene resistance in the control of wheat powdery mildew caused by Blumeria graminis (DC) E.O. Speer. Cultivar 'Knox 62' is known to have adult-plant resistance to powdery mildew, but the relationship between the genes conferring its resistance and corresponding chromosomes has not been documented. To determine the chromosomal locations of adult-plant resistance genes, Knox 62 was crossed with the susceptible disomic Chinese Spring and a full set of Chinese Spring monosomic lines. The adult plants of F₂ populations and their parents were evaluated for resistance to powdery mildew in a condition of polycyclic infection, based on their infection type (IT), infected leaf area (ILA), area under disease development curve (AUDPC) and daily disease increase index (DDII) controlled in the glasshouse. Results indicated that the resistance genes in Knox 62 are mainly additive, and 7 chromosomes were involved in the adult-plant resistance of this cultivar. Chromosomes 5A, 7A, 4B and 5D carry genes showing positive effects on resistance, while chromosomes 3A, 1B and 1D have factors increasing susceptibility. The segregation of the disomic F₂ populations and noncritical crosses fit a four-gene model, suggesting that chromosomes 5A, 7A, 4B and 5D each contain one gene or one cluster of tightly-linked genes.