Effect of Leaf Rust Resistance Gene Lr34 on Grain Yield and Agronomic Traits of Spring Wheat
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Leaf rust, caused by Puccinia recondita Roberge ex Desmaz. f. sp. tritici, is an important disease of wheat (Triticum aestivum L.) worldwide. The Lr34 gene is known to confer durable resistance. We evaluated the effect of Lr34 on grain yield and other traits in the absence and presence of leaf rust. 'Jupateco 73R' and 'Jupateco 73S' (near-isogenic reselections from the Mexican spring wheat cultivar 'Jupateco 73' for the presence and absence of Lr34, respectively) and 22 random inbred F-6 lines, 11 with and 11 without Lr34 (derived from the cross 'Jupateco 73R/Jupateco 73S'), were planted in replicated held trials during the 1992-1993 and 1993-1994 seasons in northwestern Mexico. The mean grain yield of Jupateco 73R was 5.9% lower (P < 0.05) than that of Jupateco 73S in protected plots in the 1992-1993 experiment. Significant reductions (P < 0.05) were also observed for biomass, kernels per spike and kernels m(-2). Significant (P < 0.01) reductions of 5% in mean grain yield and 3.7% in mean kernel weight were again evident in one of the two experiments sown during the 1993-1994 season. Comparison of grain yield in protected and non-protected treatments indicated that though leaf rust could significantly (P < 0.01) reduce grain yield by approximately 15% in the presence of Lr34, the reductions in the absence of Lr34 were substantially higher and ranged between 42.5 to 84% depending on planting date and year. Reductions in all other traits were also significantly higher in the absence of Lr34. We conclude that although the presence of Lr34, which is linked with leaf tip necrosis of adult plants, may carry a slight yield penalty in some disease free environments, its use in leaf rust prone areas could provide substantial protection to grain yield and other traits.
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