Submitted to: Annals Of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 27, 1998
Publication Date: N/A
Interpretive Summary: Predicting the time of flowering of field-grown soybeans that are planted at different dates is difficult. Some of the reasons for this difficulty include 1) temperature and photoperiod are variable, 2) sensitivity of different developmental stages of soybeans to temperature and photoperiod vary, and 3) flowering response to these factors is not well understood. This study examined how short-term cold temperatures imposed at different growth stages affected the vegetative and reproductive development of soybeans that were planted at two dates (April planting and July planting). Our results indicate that subsequent growth and flowering of soybean after a cold period depends on both the developmental stage at which the cold snap occurs and the planting date. Delays in flowering time were greater when cold temperatures occurred during earlier vegetative stages than during later stages and were greater in April planting than in July planting.
Technical Abstract: Predicting the time of flowering of field-grown soybean planted at different dates is difficult because the influences of photoperiod and temperature on its development are not well understood. This study examined how short-term cold temperatures affected the development of soybean (Hutcheson) under increasing and decreasing daylength conditions. In the increasing daylength study, soybean seedlings that emerged on April 10 in day-lit growth chambers (39 N lat.) were exposed to 8C for 48 h at VC, V2, V6, or V9 stage. In the decreasing daylength study, soybean seedlings that emerged on July 15 were exposed to 8C for 48 h at VE, VC, V6, or V11. The magnitudes of the changes in daylength were the same for the two experiments, but the direction of the change was opposite. All plants were kept at a 14-h thermoperiod of 28/23C. The cold treatments in decreasing daylength conditions delayed R1 and R2 stages only by 2 to 3 days. The cold treatments imposed at VC, V2, and V9 in increasing daylength conditions, however, delayed R1 by 11, 7, and 5 d, and delayed R2 by 15, 9, and 8 d, respectively. The cold treatments in both experiments delayed V stages, while final height, number of nodes, and biomass in the cold-treated plants reached the same or exceeded that of the control plants due to delays in reproductive growth. Our results indicate that subsequent growth and flowering of soybean after a cold period depends on both the developmental stage at which the cold snap occurs and the direction of changing daylength. Delays in vegetative and reproductive stages were greater when cold vegetative temperatures occurred during earlier than during later stages and were greater in increasing than in decreasing daylengths.