Seeding Date Alters Carbohydrate Accumulation in Winter Wheat

Early seeding and accumulation of soluble carbohydrates is critical for the full expression of snow mold [caused principally by Typhula incarnata Lasch ex. Fr., Typhula ishikariensis Imai, Sclerotinia borealis Bub. & Vleug., Microdochium nivalis (Ces, ex Berl. & Vogl.) Samuels and Hallet] resistance in winter wheat (Triticum aestivum L. em Thell). Experiments were conducted during two growing seasons in the field at Lethbridge, AB, to study how early seeding affects the quantity of simple sugars and fructan, and degree of fructan polymerization in both resistant and susceptible cultivars. Different planting dates were employed to obtain plants at different developmental stages prior to winter dormancy. Leaf and crown tissue samples were collected from 14 winter wheat cultivars differing in snow mold resistance throughout the autumn, winter, and early spring. Snow mold resistant cultivars accumulated moderate levels of simple sugars and high levels of fructans across seeding dates and maintained a higher degree of polymerization of fructans compared with snow mold susceptible cultivars. Early seeded treatments generally accumulated lower levels of simple sugars and higher levels of more highly polymerized fructan in the autumn and winter than did late seeded treatments. The closest correlations between snow mold resistance and fructan content (r = 0.87) or degree of polymerization (r = 0.74) were observed in the later seeded treatments, suggesting that early seeding masked the expression of genotypic snow mold resistance. These results demonstrate an association between early seeding and fructan accumulation in relation to snow mold resistance in winter wheat and provide a physiological basis for the higher level of snow mold resistance among early seeded treatments.