The effect of polyploidy on soybeans

Comparative growth-rate studies of colchicine-induced autotetraploid and diploid forms of Lincoln and Richland soybeans were conducted in the field. Comparisons among these forms also were made with respect to morphological characters, date of maturity, chemical composition, fertility, and cross-compatability. The tetraploids equalled or exceeded the height of the diploids during early stages of growth but were significantly shorter during late stages. Mean dry weight of tetraploid plants was slightly lower than diploids during early stages of growth and significantly lower during later stages. The tetraploid of each variety when compared with the normal diploid had thicker stems, longer internodes, shorter and broader leaves, larger seed and pollen, and later dates of flowering and maturity. Lateness of maturity and greater seed size were shown to be associated with, and probably attributable to, the low number of seeds per plant. Mean seed yield of Lincoln and Richland tetraploid plants was 19.3 and 12.8%, respectively, that of the corresponding diploid. Seed of the tetraploids was substantially higher in protein percentage, materially lower in oil content, and the iodine number of the oil was slightly lower than that of diploids. Tetraploids compared to diploids were lower in dry matter percentage during early and late stages of growth and not appreciably different during the middle portion of the growing period. The tetraploids and diploids appeared to be cross-incompatable. The tetraploid nature of the polyploids was confirmed by cytological examination. Induced polyploids were considered distinctly inferior to the diploids and of little value for commercial utilization. A dwarf strain which arose from a colchicine-treated seedling of the Lincoln variety was determined to contain the normal diploid complement of chromosmes, and the dwarf character was conditioned by a single recessive genetic factor.