PARTITIONING OF GENOTYPE X ENVIRONMENT INTERACTIONS OF WINTER-WHEAT FORAGE YIELD

Wheat (Triticum aestivum L. emend. Thell) is used as a dual-purpose crop in the southern Great Plains, with 35 to 55% of the acreage grazed in the fall and winter, followed by grain harvest in late spring. Cultivar selection is primarily based on grain yield. This study was conducted to characterize genotype X environment (GE) interactions for fall and winter forage production in hard red winter wheat and to identity cultivars with favorable levels of stable forage production. Eighteen cultivars were grown in six environments. Forage was clipped until the early joint stage (Feeke's 5-6), when canopy height reached almost-equal-to 20 cm. Fall forage produced prior to winter dormancy, and winter regrowth before early joint, were both influenced by GE interactions. The mean correlation of each cultivar with all other cultivars ranged from 0.91 to 0.97 for fall forage and 0.84 to 0.93 for winter forage. Based on Shukla's stability variance (sigma(i)2), three cultivars were unstable (sigma(i)2 > 0) for fall forage, whereas 10 cultivars were unstable for winter forage. Cultivars with low mean correlations were also classified as unstable. Rank stability differences for fall forage resulted primarily from three genotypes (Agripro 'Wrangler', AGSECO '7846, and 'TAM W-101') showing exceptionally high stability rather than lack of stability. Changes in rank order would not be expected to hinder selection of hard red winter wheat genotypes stable for fall forage production. Fall forage yield differences were sufficiently large to be important to wheat-stocker cattle producers.