Pod Formation in Soybeans at Low Temperatures1

Abstract

Most soybean [Glycine max (L.) Merr.] cultivars cease forming pods at temperatures near 15 C. Our research was conducted to confirm a recent report that some genotypes are capable of forming pods at lower temperatures and to determine how much extra cold tolerance these genotypes possess. A total of 36 selected genotypes were grown indoors at day/night temperatures of 25/19 C until flowering and then subjected to 2‐week treatments at temperatures of 19/15, 17/15, 15/15, 15/14, 15/13,15/12, 15/11,15/9 and 15/7 C. Six genotypes formed no pods at temperatures below 15/15 C, 12 had no pods below 15/13 C, and 18 formed pods at lower temperatures down to 15/9 C. None of the U.S. cultivars tested formed any pods below 15/13 C, with the exception of 'McCall', which formed several pods at 15/11 C. The most cold‐tolerant cultivars formed pods at 15/9 C, with two plants forming pods at 15/7 C. In all cases where pedigrees could be determined, the most cold‐tolerant genotypes were related to the Swedish cultivar ‘Fiskeby V.’Outdoor trials were planted at monthly intervals to confirm indoor rankings. Most genotypes planted on 2 January at Palmerston North, New Zealand, exhibited cold damage after one or more cold nights in February. When cold tolerance of genotypes grown outdoors was calculated as the percentage of total nodes with normal pods, this parameter was closely related (r−0.93) to the minimum temperatures at which these genotypes could form pods indoors.