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Effects of Heading Date on Agronomic Performance of Winter Wheat Isolines

Hibridos Pioneer de Mexico, S. A. de C.V. Carre. Guadalajara-Morelia km 21 8601 C.P. 45645 Tlajomulco de Zuqiga, Jal. Mexico
USDA-ARS Wheat Genetics, Quality, Physiology and Dis. Res. Unit, 209 Johnson Hall, Washington State Univ., Pullman, WA 99164-6420

^* Corresponding author (foxs{at}em.agr.ca).

Heading and photoperiod response are key processes affecting adaptiveness of wheat (Triticum aestivum L.). Few soft white winter (SWW) wheat cultivars of the U.S. Pacific Northwest (PNW) express early heading. Earliness offers several advantages including early harvest, reduced pre-harvest sprouting loss, and increased operational efficiency. The objective of this study was to determine if early heading genotypes warrant greater breeding emphasis. Near-isogenic lines (NILs) were developed by transferring early heading character from Early Blackhull and an Early Blackhull derivative to ‘Nugaines’ (NGN), an adapted PNW SWW cultivar. The NILs comprise a near-continous range of phenotypes that head 0 to 10 d earlier than NGN. The parents and NILs were tested during two to four yr in three diverse field environments. Results showed that genotypes 3 to 7 d earlier than NGN warrant increased breeding emphasis because they had high yield potential across all environments and often had enhanced test weight, kernel weight and harvest index. The earliest NILs had limited yield potential in the cool-moist medium growing season environment, but they had high yield potential in the temperate long-growing season environment. Grain-fill duration of NILs was strongly influenced by environment and only partially associated with heading date. Two early-heading NILs were less sensitive to photoperiod than NGN, but less sensitivity was not a requirement for early heading. Rate of apical meristem development was partially associated with early heading date at the distinct blister-like spikelet stage. Breeding programs centered in cool-moist environments of the PNW should consider increasing emphasis on early heading SWW germplasm.

Received for publication November 10, 1995.

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