LR46 - A GENE CONFERRING SLOW-RUSTING RESISTANCE TO LEAF RUST IN WHEAT

Wheat (Triticum aestivum) cultivar Pavon 76 carries slow-rusting resis tance to leaf rust that has remained effective in Mexico since its rel ease in 1976. 'Pavon 76' was crossed with two leaf rust-susceptible wh eat cultivars, Jupateco 73S and Avocet S, and between 118 and 148 indi vidual F-2 plant-derived F-3 and F-5 lines were evaluated for adult-pl ant leaf rust resistance at two field sites in Mexico during different seasons. Evaluation of F-1 plants and parents indicated that the slow -rusting resistance was partially dominant. Segregation in the F-3 and F-5 generations indicated that the resistance was based on two genes with additive effects. Monosomic analysis was carried out to determine the chromosomal locations of the resistance genes. For this purpose, two or three backcross-derived cytogenetic populations were developed by crossing 'Pavon 76' with a monosomic series of adult-plant leaf rus t-susceptible cultivar Lalbahadur. Evaluation of such BC2F3 and BC3F3 lines from 16 confirmed 'Lalbahadur' monosomics indicated that one slo w-rusting gene was located in chromosome 1B of 'Pavon 76'. This gene, designated as Lr46, is the second named gene involved in slow-rusting resistance to leaf rust in wheat.