Response of Tropical and Temperate Soybean Genotypes to Temperature During Early Reproductive Growth1

Abstract

Twelve soybean [Glycine max (L.) Merr.] lines of tropical and temperate origin were grown to anthesis and then subjected to a range of thermal regimes, using growth cabinets, to test their sensitivity to low temperature during early reproductive growth. Plants were grown under an 11‐h photoperiod with 30/20°C day/night, 12‐h thermoperiods prior to flowering, then during and after flowering, with all eight combinations of 20°C and 30°C day and 8, 12, 16, and 20°C night thermoperiods. There were large differential responses among lines in the sensitivity of podset to low night temperature. As a group, lines of tropical adaptation were more sensitive than temperate lines but there was variation among lines in both groups. The most sensitive (tropical) line, No. 29, failed to set pods in 8 and 12°C night temperatures while the least sensitive (temperate) line, Fiskeby V, set pods in all thermal regimes. Failure of lines to set pods in the lowest night temperatures was associated with pollen abnormalities. With the exception of Fiskeby V, there was little evidence that high day temperature compensated for the effect of low night temperature on podset. The greater sensitivity of the tropical lines to low temperature was consistent with field experience in northern Australia and it is suggested that breeding strategies for the dry (winter) season of the low latitude tropics, particularly for inland and for elevated areas, must seek to develop lines with less sensitivity to low temperature.