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Tillering, Nonstructural Carbohydrates, and Survival Relationships in Alfalfa¹

We attempted to assess the relationships of nonstructural carbohydrates and tillering with survival and productivity by identifying alfalfa (Medicago sativa L.) clones that were tolerant and others that were intolerant of frequent harvests and then comparing their response patterns. Vegetatively propagated alfalfa was grown in the field and subjected to three cutting frequencies during its second year. In autumn of 1972 when the season of cutting was completed, the plants were classified as having low, intermediate, or high tolerance to frequent cutting on the basis of survival. Plants were harvested and their roots removed from the soil. They were classified as tillering if elongated crown buds were present, and as nontillering if no elongation of crown buds were evident.

Root and crown dry weight and total nonstructural carbohydrates (TNC) content (g/plant) of the fall-harvested plants decreased from low- to high-cutting tolerance plants, but the reverse was true for TNC concentration. The patterns were the same for both tillering and nontillering plants, but in each classification, the values were 25 to 50% greater for tillering than for nontillering plants. The differences in root and crown dry weight were associated with differences in TNC content.

After the field investigation, the same clones were grown in a greenhouse. Root and crown tissues of greenhouse-cultured plants classified as frequent (those surviving frequent cutting) attained a high percent TNC soon after cutting. Clones that did not survive the frequent field cuttings (low and intermediate tolerance to frequent cutting) did not increase in crown TNC percentage in the greenhouse until flower development (or tiller initiation) had begun. Survival and production of alfalfa may be improved by selecting genotypes that produce new tillers early in the regrowth cycle.

Key Words: Medicago sativa L. • Reserve carbohydrates • Accumulation of TNC • Crown buds

² Plant Physiologist, Research Agronomist, and Research Technician, respectively, ARS-USDA, Agricultural Research Center, Light and Plant Growth Laboratory, Beltsville, MD 20705.

³ Research Agronomist, ARS-USDA, High Plains Grassland Research Center, Cheyenne, Wyo.

Received for publication April 8, 1974.