The rooting patterns of two tall and three semi‐dwarf winter wheat (Triticum aestivum L. em Thell.) cultivars were evaluated under dryland field conditions in eastern Colorado. Radioactive phosphorus (32P) was foliar applied at the soft dough stage of plant development and allowed to distribute through the root system for a 5‐ day period. Root systems were then evaluated by measuring the relative distribution of radioactivity in soil‐root cores at 30‐cm increments through the soil profile to a 300‐cm depth. Soil moisture contents, determined at harvest, were used to compare the five cultivars for associated soil profile moisture contents. We found no significant relationships between cultivar height and rooting depth or moisture extraction patterns. All cultivars rooted to a minimum depth of 300 cm both years of this experiment.

An experiment was conducted to evaluate the effect of temperature on the number of days to heading of five vernalized winter and five spring commonly grown wheat (Triticum aestivum, L. em Thell.) cultivars under an increasing daylength. Controlled environment chambers were set at 15.5 C (day) and 7.2 C (night), and 21.0 C (day) and 12.7 C (night). Temperatures, cultivars, and the temperature × cultivar interaction were all highly significant tor both days and degree‐hours to heading. Winter and spring cultivars had approximately the same range in values. All cultivars headed more rapidly at the higher temperatures. Within each growth habit, the cultivars maintained the same approximate ranking at both temperatures, but varied in their interaction with temperature. More degree‐hours were used by all cultivars at the warmer temperature indicating that only part of the increased temperature was translated into accelerated heading. Each cultivar has a specific set of phenological control mechanisms which can affect the interaction with environment in final yield expession.

Better understanding of the frequency of post‐anthesis sink‐limited winter wheat (Triticum aestivum L.) grain yields is needed in selecting genotypes with high yield potential and yield stability. Field studies were conducted at four locations (the major soil types were mesic, Aridic Paleustolls and mesic, Aridic Argriustolls) in eastern Colorado over the two cropping seasons of 1976–1977 (1977) and 1977–1978 (1978), using yield and yield component analysis, to determine the effect of sink limitations. Three hard red winter wheat cultivars were grown under four N fertilizer rates at each location to increase variation in grain yield and yield components. Variation was observed for grain yield and the yield components of spike no. (spike no. m−2), kernel no. per spike, kernel no. (kernel no. m−2), and kernel size (mg kernel−1) across locations. Grain yield and yield component variation, due to cultivars or N treatments, were observed at six of the eight sites. Variation in grain yield within and across sites was more consistently correlated with kernel no. than kernel size. These results strongly suggest that wheat grain yields may be sink‐limited during grain filling over a wide array of environments. Variation in kernel no. within locations was more consistently correlated with kernel no. per spike than spike number, while variation in kernel no. across locations was more highly associated with spike no. than kernel no. per spike. Thus, both yield components were important in establishing sink capacity under the variable environmental conditions of this study.

Microgametogenesis was compared in anthers of fertile and cytoplasmic male sterile winter wheat. Tapetal cells formed less starch and persisted longer in male sterile than in fertile anthers. Meiosis in pollen mother cells of sterile anthers was normal, but little or no starch was observed in the mature pollen. We suggest that male sterility in wheat may be caused by vascular deficiencies in the stamen.