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Carbon Dioxide Exchange and Total Nonstructural Carbohydrate in Soft White Winter Wheat Cultivars and Snow Mold Resistant Introductions¹

Experiments were conducted to investigate the relationship between snow mold resistance in winter wheat (Triticum aestivum L.) and levels of total nonstructural carbohydrates (TNC) in tissues and to test the hypothesis that TNC concentrations and resistance could be explained by increased photosynthesis or slower respiration. As a group, snow mold resistant introductions depleted TNC from tissues at a slower rate than susceptible or locally adapted soft white winter wheat cultivars. Leaves lost the greatest proportion of TNC during 20 days in darkness, whereas stem and crown TNC first declined rapidly and then declined slowly after 10 days. The pattern of TNC depletion was similar in all accessions, thus TNC translocation between tissues may play a role in resistance only when concentrations become low, and does not support the idea that TNC translocation is linked to early expression of leaf senescence observed in snow mold resistant introductions. Photosynthesis was measured on plant canopies and leaves in the tillering stage, and on flag leaves during anthesis. In all cases the cultivars as a group had the highest net photosynthesis with the exception of snow mold resistant introduction PI 181268, which ranked high for net photosynthesis in all experiments. Respiration of leaves in the dark showed a significant correlation (r = -0.71) with snow mold resistance. The correlation was negative because greater resistance was assigned a lower numerical score. Thus, the high TNC of snow mold resistant tissues cannot be attributed to slower dark respiration of leaf tissue. The selection pressures that gave rise to snow mold resistant plants have altered their TNC metabolism during overwintering, but the mechanism was not explained by changes in CO₂ exchange of leaf tissue.

Key Words: Triticum aestivum L. • Photosynthesis • Dark respiration • Carbohydrate metabolism

² Assistant scientist, Dep. of Biochemistry and Genetics, The Connecticut Agric. Exp. Stn., P.O. Box 1106, New Haven, CT 06504.

Received for publication August 11, 1986.

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