Harvest Indexes of Backcross‐Derived Wheat Lines Differing in Culm Height1

Abstract

The high grain yields of some short‐statured small grain cultivars have been ascribed to their improved harvest index (HI) values. This study determined the influence of genetic backgrounds and genes (Rht1, and Rht2) for semidwarf culm height on HI of wheat (Triticum aestivum L.). The HI was measured in four tests on progeny of seven backcross‐derived populations (six backgrounds). The progeny consisted of three culm height classes designated as two‐gene semidwarf(short), one‐gene semidwarf(medium)a, nd normal( tall). Lines with Rht1 or Rht2 genes either singly or in combination had significantly higher HI values than their normal (nonsemidwarf)sibs in 45 of 56 comparisons. Short two‐gene semidwarf lines had significantly higher HI values than their one‐gene and normal counterparts in 9 of 28 and 25 of 28 comparisons, respectively. One‐gene semidwarf lines exceeded HI values of their normal sibs for 20 of 28 comparisons. When calculated across tests and populations, the HI means of two‐gene semidwarf, one‐gene semidwarf, and normal lines were 41.4, 38.0 and 31.6, respectively. The two‐ and one‐gene semidwarf doses increased HI by 31 and 20%,r espectively. The HI values of the inherently taller backgrounds were increased proportionately more than shorter backgrounds by addition of one or two doses of semidwarf genes. The HI of the ‘Marfed’ background was increased most by addition of the Rhtl and Rht2 genes. Based on simple correlations, the use of HI as a selection criterion for grain yield appeared more feasible among inherently taller than shorter backgrounds. Because all interactions among tests, populations and height classes were significant, selection for greater HI may be tenuous.