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Effect of Variety, Seed Lot, Soil pH, Soil Fertility, and Light on Cotyledon and Plant Color in Alfalfa¹

Environmental conditions such as light intensity, temperature, soil pH, and fertility significantly affected the expression of alfalfa plant and cotyledon color. Soil pH and soil fertility had only minor effects on cotyledon color. Plant color was affected to a greater extent, plants grown on limed and fertilized soil being about 20% darker, i.e., acetone extracts of leaf tissue averaged about 20% less transmission than those grown on a relatively acid (pH 5.6) and infertile soil. Plants grown in growth chamber at alternating 18 and 9 C with light for 14 hours at the higher temperature were significantly darker than those grown in a warm greenhouse (25 to 20 C) and 24-hour photoperiods. Differences in cotyledon and plant color associated with seed lot were relatively minor. When grown and sampled under standardized conditions, varieties derived in part from Medicago falcata such as ‘Vernal’ and ‘Narragansett’ were generally darker green than varieties derived from Medicago sativa. Measurements of cotyledon and plant color in 10 common varieties of alfalfa indicated the presence of significant varietal differences. Results of these studies indicate that colorimetric measurements of cotyledon and plant color can be used to separate alfalfa varieties into groups. Additional tests can then be applied to further characterize varieties within each group. Cotyledon color was of lesser value for this purpose than plant color.

Key Words: Leaf color • Varietal differences • Colorimetric

² Graduate Assistant and Associate Professor respectively, Department of Agronomy, The Pennsylvania State University. K. P. Sheridan is presently Research Officer, Agricultural Research Station. New South Wales, Department of Agriculture, Tamworth, N. S. W., Australia.