Periods of Shoot Chilling Sensitivity in Soybean Flower Development, and Compensation in Yield after Chilling

Soybeans [Glycine max (L.) Merr. cv. Ransom] grown at a constant 25 °C were placed in a 12-h inductive photoperiod at two weeks of age. Subgroups were shoot-chilled for one week at a constant 10 °C during each of the first four weeks of floral induction. Controls were photoinduced but not chilled. Chilling during the first week of photoinduction inhibited production of floral primordia, but did not increase the abscission rate of flowers and pods. Chilling during the second week did not affect primordium production or abscission rate, but did cause a significant increase in numbers of fused and malformed pods. Chilling during the third week caused loss of 77 per cent of early flowers and pods by abscission, while fourth week chilling caused less severe losses by abscission. Inhibition of vegetative growth may have been responsible for primordium loss in first-week plants, while disturbances in the development of flowers were responsible for the losses in the other chilling weeks. Although chilling during the first and third photoinduction weeks caused a significant reduction in early pod numbers, plants harvested at 16 weeks of age showed no significant loss in seed yield. Low abscission rates late in pod filling and increased weight of individual seeds compensated for early losses of pods. These compensatory responses to a chilling-induced loss of pods are similar to those reported for mechanically depodded soybeans.