Leaf Rust Resistance Gene Lr9 and Winter Wheat Yield Reduction: I. Yield and Yield Components

Abstract

Leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) resistant near isogenic lines (NIL) of wheat (Triticum aestivum L.) have generally lower yields than the susceptible recurrent parent under disease free conditions. Analysis of growth and yield should increase our understanding of the reduced yielding ability of NIL. In a 3‐yr field study, the yield components of the leaf rust susceptible cultivar Arina were compared with six resistant NIL carrying the resistance gene Lr9 introduced from Aegilops umbellulata. The NIL were derived from two independently developed backcross populations with Arina as the recurrent parent. The NIL were phenotypicaily very similar to Arina. At anthesis and at mediumilk stage, the total aboveground dry matter was similar for the NIL and Arina. Differences in the dry matter accumulation appeared only after the medium milk stage. At maturity, the NIL had a 12% lower grain yield than Arina (5.88 ha−1) with a range from 5 to 14%. The lower grain yield resulted from a 3 to 11% reduction in grain number per square meter and a 2 to 7% reduction in mean grain weight. The smaller grain number per square meter was the result of a 6% smaller tiller number per plant and a 2% smaller grain number per ear. Artificially reducing grain number per ear suggested that both a reduced supply of assimilates and a diminished capacity to incorporate assimilates in the grain caused the reduced grain yield of the NIL. Deleterious effects of alien genes linked with the Lr9 gene from Aegilops umbellulata cannot be ruled out. However, the small differences within and between the NIL of the two Lr9 populations for the parameters tested suggest a direct relation between the yield depression and the leaf rust resistance conferred by the Lr9 gene.