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Effects of Natural Selection and the Relationship of Leaf Traits with Yield in Hard Red Spring Wheat Crosses¹

The F₂ through F₄ bulks of five crosses between adapted hard red spring wheats (Triticum aestivum L.) were grown in solid-seeded competitive conditions for 3 years in two contrasting environments. One environment (East) was characterized by conditions which imposed relatively infrequent moisture stress and the other (West) in which moisture stress was common. The five East derived bulks (East Bulks), the five West derived bulks (West Bulks), and 25 F₃derived lines from each bulk (East and West Lines) were evaluated for yield and other characteristics for 2 years at East and West sites to detect possible differential natural selection. The mean yield of the West Bulks was significantly greater than yield of the East Bulks at the West test site, while East and West Bulks yielded similarly at the East site. No differences, however, were detected between the mean yields of East and West Lines over crosses at either site. Short term natural selection failed to aid in the extraction of more adapted lines. In two crosses segregating for photoperiod reaction, the West Lines had a significantly greater proportion of insensitive genotypes than expected. Evidently natural selection favored insensitive types in the more droughty West environment. Stomatal frequency, stomatal diffu. sion resistance, and other leaf characteristics were measured in the East environment to determine if any leaf trait measured in the East was indicative of yield in the more droughty West conditions. No consistent relationships were noted between the yield of lines in the West and any leaf characteristics or combination of characteristics in the East.

Key Words: Triticum aestivum L. • Stomatal frequenc • Stomatal diffusion resistance • Photoperiod reaction • Genotype x environment interaction

² Former graduate research assistant (present address: Cell Culture and Nitrogen Fixation Laboratory, Building 001, Beltsville Agric. Res. Center-West, Beltsville, MD 20705), and professor, Dep. of Agronomy, North Dakota State Univ., Fargo, ND 58102 (Currently: research geneticist, SEA, USDA, Dep. of Agrouomy and Plant Genetics, Univ. of Mimacsota, St. Paul, MN 55108.

Received for publication January 26, 1978.