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Agronomic Comparisons Between Rht₁ and Rht₂ Semidwarf Genes in Winter Wheat

USDA-ARS, Wheat Genetics, Quality, Physiology and Disease Res. Unit, Pullman, WA 99164-6420

^* Corresponding author.

The Rht_l and Rht₂ semidwarf genes have been the most extensively exploited factors for reducing height of wheat (Triticum aestivum L.). These genes have been used singly to develop hundreds of modern wheat cultivars. Information is limited on their relative breeding value. This study measured the effects of the Rht₁ vs. the Rht₂ gene on grain yield, grain yield components, lodging, crown placement, and stand establishment. Near isogenic lines of the four possible genotypes (Rht₁Rht_lrht₂rht₂, rht₁rht₁Rht₂Rht₂, Rht₁Rht₁Rht₂Rht₂, rht₁rht₁rht₂rht₂) of four or five winter wheat populations representing three genetic backgrounds were tested in 15 trials conducted during 1976 to 1978 at several diverse environments in Washington. Compared to their rht₁rht₁rht₂rht₂ sibs, Rht₁Rht₁rht₂rht₂ and rht₁rht₁Rht₂Rht₂ isolines had similar average grain yield increases of 16% while the average increase of Rht₁Rht₁Rht₂Rht₂ isolines was only 2%. Mean differences in grain yield, grains spike^–1, grain weight, crown placement, and lodging percentage were not significant (P > 0.05) between Rht₁Rht₁rht₂rht₂ and rht₁rht₁Rht₂Rht₂ isolines among or across populations. When averaged across populations, mean plant heights of rht₁rht₁Rht₂Rht₂ isolines were 2% shorter (P < 0.05) than Rht₁Rht₁rht₂rht₂ sibs. Generally, means for grain volume weight, emergence rate, and final stand of Rht₁Rht₁rht₂rht₂ isolines exceeded those of rht₁rht₁Rht₂Rht₂ isolines. These differences were not due to pleiotropic effects of the two genes because population x Rht₁ vs. Rht₂ loci interactions occurred for each trait. From a breeding standpoint, use of Rht₁ is warranted because it generally had less adverse effect on grain volume weight and stand establishment than Rht₂.

Received for publication October 31, 1989.

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