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Selection for High and Low Harvest Index in Three Winter Wheat Populations¹

Low heritability of grain yield in wheat (Triticum aestivum L.) often results in a slow response to selection. Selection criteria other than grain yield per se are being sought by wheat breeders. Harvest index (HI), the ratio of grain yield to total biomass yield, may be a useful selection trait for yield improvement. A study was undertaken to estimate the heritability of HI and to determine the response to selection for high and low HI in three genetically diverse populations of winter wheat. Selections were made in the F₃ generation and selected progenies were evaluated in replicated tests in the F₄ generation. Realized heritability estimates for HI were intermediate in magnitude (0.44 to 0.60). Selection in F₃ for high and low HI was effective in identifying F₄ lines with high and low HI, respectively. Also, selection for high HI resulted in shorter plants with earlier heading dates and lower biomass yield. Genotypic correlations (rG) between HI and grain yield were low (rG = 0.04 to 0.23). Phenotypic correlations between HI and grain yield were relatively high in the F₃ but much lower in the F₄. Harvest index was negatively correlated with plant height and days to heading, while correlations between HI and biomass yield were mostly nonsignificant. Simple correlation coefficients between F₃ and F₄ means were higher for HI than for grain yield. Results indicated that HI in the F₃ generation was a good predictor of HI in the F₄, but a poor predictor of grain yield in the F₄.

Key Words: Triticum aestivum L. • Realized heritability • Selection response • Grain yield • Assimilate partitioning • Genotypic correlation

² Research associate and professor of agronomy, respectively, Oklahoma State Univ., Stillwater, OK 74078.

Received for publication January 17, 1986.