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Influence of the Rht1 Semidwarf Gene on Yield, Yield Components, and Grain Protein in Durum Wheat¹

Many wheat breeding programs in the world utilize semidwarf germplasm to improve productivity and lodging resistance. Four sources of the reduced height gene Rhtl, were crossed with a conventional height cultivar to determine the influence of this gene on yield, yield components, test weight, and grain protein in durum wheat (Triticum turgidum L. var durum). Seedlings having the Rhtl/Rhtl (semidwarf) or rhtl/rhtl (tall) genotype were selected in the F₂ generation of each cross based on their sensitivity to gibberellic acid. The F₂-derived F₄ families were evaluated during the 1981 and 1982 field seasons. The semidwarf and tall height classes differed significantly for yield, test weight, kernel weight, tiller number, height, kernels per spike, spike length and grain protein. Semidwarfs produced significantly greater yield, number of tillers, and kernels per spike than the tall height class. The difference in tillering was found in only two of the four crosses and thus was not a general trend. Tall lines had consistently higher test weight, kernel weight, and grain protein than semidwarf lines. A positive correlation was observed between plant height and grain protein concentration (r=0.80, p<0.01). Factors in addition to the dilution of the protein in the kernel due to high yield are responsible for the low grain protein concentration associated with semidwarfs because low yielding semidwarf lines had significantly lower grain protein concentration than the high yielding tall lines. The use of the Rhtl gene in durum wheat breeding programs may contribute to higher grain yield in the absence of lodging but reduced grain protein levels may become a serious quality problem.

Key Words: Triticum turgidum L. var durum • Plant height • Dwarfing gene • Pleiotropism • Test weight • Kernel weight • Kernel per spike • Tiller number

² Formerly graduate research assistant, and assistant professor of agronomy, respectively, North Dakota State Univ., Fargo, ND 58105; professor of agronomy, Colorado State Univ., Ft. Collins, CO; and Principal scientific officer, Plant Breeding Inst., Cambridge, England.

Received for publication September 23, 1985.