The Rht l and Rht 2 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 Rht 1 vs. the Rht 2 gene on grain yield, grain yield components, lodging, crown placement, and stand establishment. Near isogenic lines of the four possible genotypes ( Rht 1 Rht l rht 2 rht 2 , rht 1 rht 1 Rht 2 Rht 2 , Rht 1 Rht 1 Rht 2 Rht 2 , rht 1 rht 1 rht 2 rht 2 ) 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 rht 1 rht 1 rht 2 rht 2 sibs, Rht 1 Rht 1 rht 2 rht 2 and rht 1 rht 1 Rht 2 Rht 2 isolines had similar average grain yield increases of 16% while the average increase of Rht 1 Rht 1 Rht 2 Rht 2 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 Rht 1 Rht 1 rht 2 rht 2 and rht 1 rht 1 Rht 2 Rht 2 isolines among or across populations. When averaged across populations, mean plant heights of rht 1 rht 1 Rht 2 Rht 2 isolines were 2% shorter (P < 0.05) than Rht 1 Rht 1 rht 2 rht 2 sibs. Generally, means for grain volume weight, emergence rate, and final stand of Rht 1 Rht 1 rht 2 rht 2 isolines exceeded those of rht 1 rht 1 Rht 2 Rht 2 isolines. These differences were not due to pleiotropic effects of the two genes because population ✕ Rht 1 vs. Rht 2 loci interactions occurred for each trait. From a breeding standpoint, use of Rht 1 is warranted because it generally had less adverse effect on grain volume weight and stand establishment than Rht 2 .
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R. E. Allan (1989) studied this question.