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Early Season Cold Tolerance in Soybean¹

Early planted soybean [Glycine max (L.) Merr.) frequently encounters cold soil conditions. Several reports indicate soybean genotypes differ in rates of germination in the growth chamber at low temperatures and in early field plantings. However, in each experiment only one seed source was used. The objectives of our experiments were: i) to examine the effect of seed source environment on cold germination ratings in the growth chamber and on field performance at early plantings; ii) to compare genotypes from the Midwest and foreign countries for cold germination tolerance; iii) to determine if oil or protein concentration, seed size, or date of harvest were correlated with cold germination data; and iv) to compare growth chamber cold germination measurements with field performance at early plantings. Twenty diverse genotypes were grown at five locations in each of 2 yrs. Seed samples from these plantings were tested for rate of germination at 10°C in the growth chamber in a randomized complete block design. Analysis of germination indexes showed highly significant genotype and genotype x location effects each year. The subset of foreign accessions were more consistent in germination cold tolerance ratings than the subset of North American genotypes. Only oil concentration showed a small significant positive correlation with cold germination. The same 20 genotypes were planted in the field in a randomized complete block as early as possible in 1982 and 1983. Significant genotypic differences were observed both years in field performance. Growth chamber germination ratings and field data means were rarely correlated. Our data suggest that selection against poor emergence or vigor under cold conditions seems more practical in most cases than selection for good emergence or vigor. Several seed sources should be used when evaluating genotypes for early season cold tolerance.

Key Words: Glycine max (L.) Merrill • Germination index • Emergence index

² Former graduate research assistant (presently, assistant professor of Horticulture, Univ. of Puerto Rico, Mayaguez, PR 00708); associate professor, and emeritus professor, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication July 3, 1985.