LEAF RUST RESISTANCE GENE LR9 AND WINTER-WHEAT YIELD REDUCTION .1. YIELD AND YIELD COMPONENTS

Leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) resistant near isogenic lines (Nn) of wheat (Triticum aestivum L.) have generall y lower yields than the susceptible recurrent parent under disease fre e conditions. Analysis of growth and yield should increase our underst anding of the reduced yielding ability of NIL. In a 3-yr held study, t he yield components of the leaf rust susceptible cultivar Arina were c ompared with sir resistant hn, carrying the resistance gene Lr9 introd uced from Aegilops umbellulata. The NIL were derived from two independ ently developed backcross populations with Arina as the recurrent pare nt. The hit were phenotypically very similar to Arina. At anthesis and at medium milk stage, the total aboveground dry matter was similar fo r the NIL and Arina. Differences in the dry matter accumulation appear ed only after the medium milk stage. At maturity, the Nn had a 12% low er grain yield than Arina (5.88 t ha(-1)) with a range from 5 to 14%. The lower grain yield resulted from a 3 to 11% reduction in grain numb er 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 t ilter number per plant and a 2% smaller grain number per ear. Artifici ally reducing grain number per ear suggested that both a reduced suppl y of assimilates and a diminished capacity to incorporate assimilates in the grain caused the reduced grain yield of the ML. Deleterious eff ects of alien genes linked with the Lr9 gene from Aegilops umbellulata cannot be ruled out. However, the small differences within and betwee n the NIL of the two Lr9 populations for the parameters tested suggest a direct relation between the yield depression and the leaf rust resi stance conferred by the Lr9 gene.