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Relation of Flag Smut Incidence to Semidwarf Growth Habit in Wheat Isolines¹

Incidence of flag smut [Urocystis agropyri (Preuss) Schroet.] was related to the presence of semidwarf genes of wheat (Triticum aestivum L. em. Thell.) derived from ‘Norin 10’/‘Brevor,’ 14 and ‘Suwon 92.’ For 2 years at two sites, tests were conducted on five isoline populations of four genetic backgrounds with varying degrees of flag smut susceptibility. Isolines with two semidwarf genes had higher incidences of smut than standard-height phenotypes in 9 of 10 comparisons (P = 0.05). One-gene semidwarf isolines were more heavily smutted than standard-height lines in 7 of 10 comparisons (P = 0.05). The two-gene, one-gene semidwarf, and standard-height phenotypes averaged 62.9, 56.3 and 47.6% smutted tillers, respectively, for all populations during the 2 years. The proportions of smuttedtillers of all populations for both years for two-gene and one-gene phenotypes vs. the standard-height phenotypes were 1.32 to 1.00 and 1.18 to 1.00, respectively. The two-gene semidwarf isolines were significantly more heavily smutted than their one-gene semidwarf sibs in 6 of 10 comparisons (P = 0.05). On an overall basis, the proportion of smutted tillers of the two-gene vs. one-gene phenotype was 1.12 to 1.00. The relation between semidwarf genes and increased incidence of flag smut was indirect and should not preclude the development of two and one-gene semidwarf cultivars with adequate resistance. Breeders should recognize that semidwarf types may be potentially more vulnerable to losses from flag smut than nonsemidwarf types.

Key Words: Genetic background effects • Backcross • Seedling vigor • Urocystis agropyri (Preuss) Schroet. • Triticum aestivum L. em. Thell

² Geneticist, ARS, USDA, Pullman, WA 99163.

Received for publication November 11, 1974.