The wheat selection C. I. 14106, which is resistant to parents and Nugaines in carbohydrate accumulation during Typhula idahoensis, accumulated available carbohydrates in cold hardening, carbohydrate use under snow mold its crown tissues early in the cold-hardening process; but conditions, and in resistance. This indicated no cytoplasmic resistant C. I. 9342, moderately resistant Moro, and inheritance either of resistance or of patterns of carbohydrate susceptible Nugaines accumulated less carbohydrates and at metabolism. Resistance in Fls was partially dominant. Only a slower rate. Early acquisition of carbohydrate in the crown F 1 progeny of C. I. 14106 accumulated carbohydrates of C. I. 14106 was correlated with early acquisition of rapidly. Under snow mold conditions, progenies of C. I. resistance. Moro and C. I. 9342 required longer periods of 14106 and C. I. 9342 used carbohydrate at a slower rate after cold hardening to acqu!ire Carbohydrates and resistance. 3,Q days than did Nugaines. There was no correlation between During incubation at 0.5 C •ih Athe dark, carbohydrate snow mold resistance and crown carbohydrate content of 15 concentration declined in Nugaines at a faster rate than in C. wheats sampled in the field in early autumn, but there was a I. 14106, C. I. 9342, or Moro. The F, progeny of reciprocal high correlation if they were sampled in the spring after snow crosses were intermediate between their respective resistant melt. Winter wheats (Triticum aestivum L.) with useful inefficient in increasing resistance in the susceptible resistance to snow mold fungi (Typhula idahoensis Nugaines wheat (5). Remsb., Typhula ishikariensis Imai, Typhula incarnata Resistant wheats use their reserves at a slower rate in Lasch ex Fr., Fusarium nivale (Fr.) Ces., and Sclerotinia darkness near 0 C than do susceptible wheats (6). It was borealis Bubak & Vleugel) exist (7, 8) and they have been suggested that leaves of susceptible wheats use the subject of a recent review (10). Genetic studies of carbohydrates more readily than leaves of resistant resistance in winter wheat to T. idahoensis indicate plants, thus depriving crowns of a translocatable source quantitative inheritfiace involving several genes for of carbohydrate (0). Tomiyama (19) showed that resistance (8). Cultivars resistant to T. idahoensis also are susceptibility to T. incarnata increased as carbohydrates resistant to T. incarnata and F. nivale (3, 4). There is also were exhausted and proteolysis in leaves increased; a correlation of resistance in cereals to T. ishikariensis, T. resistance thus terminated when leaf tissues became incarnata, F. nivale, and S. borealis in Scandinavia (10). senescent. Similar results have been reported for T. The wide host ranges of these fungi, in some cases not incarnata on winter barley (12). On the other hand, field restricted to the Gramineae, is also evidence for a lack of observations of C. I. 9342 and C. I. 14106 suggested that high degrees of pathogenic specialization (4, 10). No resistance in C. I. 9342 is i...

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Yield differences among New York winter wheat (Triticum aestivum L.) are related to harvest index. This study was conducted to see how four cultivars, which differed in harvest index and plant height, differed in partitioning of photosynthate before and during grain filling. Experiments were conducted in field plots grown at Hamden, CT in 1985 and 1986 in Cheshire fine sandy loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). The assimilation, distribution, and retention of radioactivity from 14CO2‐derived photosynthate was measured. In each year, the canopy was labeled at heading and early and late in grain filling. Harvest index was inversely related to stem height. The fractional distribution of the 14C remaining at maturity varied with labeling date and cultivar. The amount in the spike was 0.35 to 0.5 when labeled at heading, with less than 0.15 in the grain. When labeled during grain filling, a greater fraction of 14C was distributed to the spike in the semidwarf than in the tall cultivars, 0.9 and 0.8, respectively, and most of the 14C in the spike was in the grain. Almost half of the radioactivity initially assimilated was lost from the plants by maturity. Tall semi‐dwarf ‘Purcell’ retained a greater fraction of radioactivity initially assimilated than did tall ‘Honor’, 0.56 and 0.51, respectively. Thus, differences in harvest index were related to differences in distribution of photosynthate and to differences in retention of photosynthate to maturity.