Effect of temperature and daylength on phenology for contrasted soybean genotypes grown in Europe

European Union (EU-28) needs to import about 40 million tons of soybean (seed equivalent.year-1) to feed livestock and population to a lesser extent. Since a few years, soybean production in Europe bas largely încreased but remains still insufficient. In a context of climate change, southem areas tend to face more drought and heat waves while northem ones will benefit from higher temperatures in late season. Three other cropping strategies could be considered to grow soybean under these conditions: early sowing to escape drought, north\vard expansion of the crop, or double cropping. This witl change decply the photoperiod and temperature conditions during the crop season. As soybean is a tropical short-day plant, it is important to understand the temperature-photoperiod interactions on phenology for current genotypes gro\vn in Europe (under long daylengths and contrasted temperatures). For that, a study was conducted in INRA Toulouse (SVl France), combining fine phenotyping on an outdoor platform and in controlled conditions. In 2017, two experiments were carried out using 10 contrasted genotypes from maturity groups 000 to II : 1-A pot experiment on the Heliaphen platform in natural climatic conditions \.vhere germinated plants were transplanted at 6 dates (17-march, 6-april, 16-may, 26-june, 24-july, lst-september). Pots were fully fertilized and irrigated during ail the experiment. Development stages \Vere recorded once or twice a week (BBCH scale). 2- A germination experiment in cold chamber/incubator. 1 OO seeds by genotype were incubated at 10 temperatures (from 4 to 43°C) in Petri dishes on moist paper. The germinating seeds were counted tv-iice a day. Gennination results were used to calculate the base temperature of each genotype (Tb from 4.6 to 6.7°C). This information was essential for the relevant calculation of the onset of each development stage and the duration of phases expressed in growing degree days (GDD). For most stages, ANOVA analysis pointed out a highly significant effect of genotype by planting date interaction on GDD accumulation. The results showed that GDD accumulation from cotyledon stage to maturity (BBCI! stage 10 to 80) was impacted more by planting date (cv ~ 16%, p < 0,001) than by genotype (cv ~ 10 %, p < 0,001). In addition, the difference across genotypes steadily decreased when daylenght \Vas reduced by later sowing dates (from 14.5 to 12.5 h). These results will be used first to calibrate phenological models then different crop gro\vth models, These models will be necessary to test a wider range of "genotype x environment x management" combinations with the perspective of designing suitable cropping areas and ideotypes for soybean in France and Europe