Soybean Genotype-Specific Cold Stress and Priming Responses: Chlorophyll a Fluorescence and Pigment-Related Spectral Reflectance Indices as Tools for Breeding

Early sowing to avoid stress later in the season is limited by low early spring temperatures and unpredictable cold spells within recommended sowing dates. To achieve successful crop production, it is essential to understand plant stress responses, enabling breeders and producers to better address climate change challenges. Researching genetic variability for cold stress is key to developing cold-tolerant crops. In response, a study investigating the effects of low-temperature treatment and cold priming in the early vegetative development on soybean biomass, chlorophyll a fluorescence (ChlF) and pigment-related spectral reflectance indices (PR_SRIs) was conducted in a controlled environment with 12 soybean genotypes. Priming began 16 days after sowing (DAS), followed by a 48-h recovery and a subsequent 48-h low-temperature treatment. During priming and stress treatments, temperatures and relative air humidity were set to 10/5 °C and 70/90% (day/night), with a light intensity of 300 μmol/m2/s. The results showed that low temperatures negatively impacted biomass and physiological parameters, with priming having neutral or negative effects. The parameters ET0/TR0, RE0/RC, TR0/DI0, Fm, Fv, ARI1, and ARI2 were identified as relatively appropriate non-destructive alternatives for biomass analysis, aiding in genotype screening and stress detection. Genotypic variation in response to cold stress suggests potential for selecting cold-tolerant varieties.