Day and Night Temperature Influence on Carpel Initiation and Growth in Soybeans

Abstract

Cool temperatures can modify soybean (Glycine max [L.] Merrill) reproductive potential by influencing flower and pod abscission and certain floral aberrancies such as cleistogamy and cleistoflory, as well as by affecting growth rates. Under the cool day/night temperature combination of 18/14 C, floral development is often disrupted, leading to physically malformed pods, and frequently more than one carpel is initiated in a flower. To document the effect of temperature on carpel initiation and development, data were obtained from plants grown at 25 day/night temperature combinations over a range of 14-30 C day temperatures and 10-26 C night temperatures. Plants of the determinate soybean 'Ransom' were grown under long-day, noninductive photoperiods until expansion of the third trifoliolate leaf, then transferred to short-day conditions for the remainder of the experiment. After 9 wk, flowers from the terminal racemes of all plants were examined for normal, misshapen, and multiple carpel development. The nine day/night temperature combinations from 14, 18, and 22 C days and 10, 14, and 18 C nights produced 75%-100% multiple carpellate flowers. Normal floral initiation and pod development occurred when the warm night of 26 C was combined with any of the day temperatures, and also at 30/18 and 30/22 C. Pod length increased with increases in either day or night temperature. Average dry weight accumulated per pod, however, was optimal at 26/22, 26/26, and 30/22 C, while the greatest number of pods per plant was obtained at 30/14 and 26/14 C.