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

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Abstract
Cool temperatures can modify soybean (G. 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.degree. C, floral development is often disrupted, leading to physically malformed pods, and frequently more than 1 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.degree. C day temperatures and 10-26.degree. C night temperatures. Plants of the determinate soybean ''Ransom'' were grown under long-day, noninductive photoperiods until expansion of the 3rd 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 9 day/night temperature combinations from 14, 18 and 22.degree. C days and 10, 14 and 18.degree. C nights produced 75-100% multiple carpellate flowers. Normal floral initiation and pod development occurred when the warm night of 26.degree. C was combined with any of the day temperatures, and also at 30/18 and 30/22.degree. C. Pod length increased with increases in either day or night temperature. Average dry weight accumulated per pod, was optimal at 26/22, 26/26 and 30/22.degree. C, while the greatest number of pods per plant was obtained at 30/14 and 26/14.degree. C.