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Effects of Locations and Years upon Relative Yields in the Soft Red Winter Wheat Region¹

Yields of entries in the Uniform Eastern Soft Red Winter Wheat (Triticum aestivum L. em Thell) Nursery at 12 locations were correlated with corresponding yields at each of the other locations for 7 years to access the relative yield response at various locations and to determine the influence of years upon relative yields at locations. All but one of 66 location pairs (Madison, Wis. Blacksburg, Va.) exhibited a significant positive correlation in at least 1 year and only one location pair (Lafayette, Ind.-South Charleston, Ohio) showed a significant positive correlation for all 7 years. Sixteen location pairs were significantly correlated (positive) in 5 or more years. A cluster analysis based upon the 7-year mean correlation coefficients indicated that relative yields were similar at Lafayette, Ind., Urbana, Ill., and Columbia, Mo. and that Keiser, Ark., Madison, Wis., and Blacksburg, Va. were most unlike other locations in the region. An average of correlation coefficients including all location pairs with a common location indicated that Lafayette, Ind. and South Charleston, Ohio would be favorable sites for breeding and testing for wide adaptation; whereas, Madison, Wis. and Blacksburg, Va. may require traits not generally needed for adaptation throughout the region. Averages of correlation coefficients within a year indicated that relative yields were more uniform throughout the region in some years (1970, 1972, and 1975) than hi others (1971). An examination of ‘Knox 62’ yield relative to the mean yield in individual environments was used as an indicator of the reliability of cultivar characterization based upon 3 years of testing. Regression coefficients (Knox 62 vs. environment mean) were consistently lower in combinations of years including 1972 while 1974 produced higher values. Coefficients of determination (r²) were lower in periods including 1975 and higher in combinations including 1974. Neither measure of yield stability appeared to be related to yield level. The data supported an extensive testing program and makes apparent the need to test over years to adequately characterize cultivars.

Key Words: Regional performance nurseries • Adaptation • Genotype x environment interactions • Triticum aestivum L. em Thell.

² Formerly post-doctoral research associate in agronomy (presently research geneticist, SEA, USDA, North Dakota State Univ., Fargo, ND 58105) and professor of agronomy, respectively, Dep. of Agronomy, Ohio Agric. Res. and Dev. Ctr., Wooster.

Received for publication May 13, 1979.

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