Partial race non-specific resistance to rust diseases and powdery mildew in wheat is valuable in providing cultivars with durable resistance. Partial resistance is inherited as a quantitative trait, and the success of breeding for this type of resistance is based on the ability of resistance genes to complement each other and provide offspring with increased levels of resistance. The objective of the present study was to investigate
the additivity of rust resistance genes in two mapping populations that segregated for resistance at the Lr34 and Lr46 loci: ‘Avocet x Parula’ and ‘Avocet x Saar’. The former also segregated for a third resistance gene on chromosome 7BL from Parula, designated LrP. The populations were tested for resistance to leaf rust, stripe rust and powdery mildew in multiple environments across Mexico, the Southern Cone of South America,
Norway and China. Lr34 showed consistent effects on resistance to all three diseases in both populations and across all environments. LrP also showed consistent effects on leaf rust in all environments where it was tested, and contributed additively to improved resistance when combined with other genes. Lr46 conferred resistance to all three diseases, but the magnitude of effect was always less than that for Lr34. Combinations of Lr34 and Lr46 resulted in only slight improvements in resistance over Lr34 alone. We conclude that partial resistance genes with different mechanisms need to be combined to achieve a stable resistance performance across environments.

Global Wheat Program

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INT2833|INT0610