Comprehensive evaluation of low-temperature tolerance in soybean cultivars of different eco-types at seedling stage in Shanxi Province

Abstract

Aims Low temperature at the seedling stage is the key factor constraining growth and yield in spring-sowing soybeans (Glycine max) in North China. The objectives of this research were to explore responses of soybean cul- tivars of different eco-types in Shanxi Province to low temperatures at the seedling stage, to develop indices and approaches for comprehensive evaluation of low-temperature tolerance in soybeans, and ultimately to provide theoretical basis for breeding soybean cultivars of low-temperature tolerance in order to maintain stable yield un- der the conditions of low temperature stress at the seedling stage. Methods We selected three soybean cultivars ('Jinda 53', 'Jinda 70' and 'Jindou 24') bred and grown widely in Shanxi Province. At the seedling stage, the plant materials were subjected to stress treatments at three levels of low temperatures and a control treatment in growth cabinets. The low temperature treatments were set for 14, 17 and 20 °C, respectively, and the control treatment was maintained at 23 °C. Upon completion of the temperature treatments, the seedlings were transplanted into larger pots and grown in a greenhouse. Values of photosynthetic traits (including net photosynthetic rates (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and transpiration rate (Tr)) were determined on seedlings. The yield traits (plant height, plant mass, pods per plant and yield per plant) were assessed after harvesting. Furthermore, the genotype main effect plus genotype-environment interaction (GGE) biplot was employed to analyze the effects of various traits on different cultivars and correla- tions among the traits. Then, subordinate function was applied for comprehensive evaluation of low-temperature tolerance of the three cultivars studied. Important findings (1) The seedling stage of all three cultivars was extended by 1-12 days by the low tempera- ture treatments. (2) Values of the four photosynthetic traits were reduced in seedlings subjected to low temperature treatments; the rate of reduction was significantly greater for Gs and Tr than for the other two traits. Reductions in the values of photosynthetic traits were significantly smaller in the cultivar 'Jinda 53' than in other two cultivars, suggesting the stronger low temperature tolerance of this cultivar in terms of photosynthetic capacity. Addition- ally, 'Jinda 70' maintained higher Pn values than the other two cultivars, which was beneficial to greater dry mat- ter accumulation in this cultivar. (3) Values of the four yield traits were all significantly reduced in plants