Abstract
Soybean (Glycine max L.) seedlings may be exposed to low or high temperatures under early or conventional soybean production systems practiced in the US Midsouth. However, a wide range of soybean cultivars commonly grown in the region may inherit diverse tolerance to degrees of temperatures. Therefore, a study was conducted in a controlled-environment facility to quantify 64 soybean cultivars from Maturity Group III to V, to low (LT; 20/12 °C), optimum (OT; 30/22 °C), and high (HT; 40/32 °C) temperature treatments during the seedling growth stage. Several shoot, root, and physiological parameters were assessed at 20 days after sowing. The study found a significant decline in the measured root, shoot, and physiological parameters at both low and high temperatures, except for root average diameter (RAD) and lateral root numbers under LT effects. Under HT, shoot growth was significantly increased, however, root growth showed a significant reduction. Maturity group (MG) III had significantly lower values for the measured root, shoot, and physiological traits across temperature treatments when compared with MG IV and V. Cultivar variability existed and reflected considerably through positive or negative responses in growth to LT and HT. Cumulative stress response indices and principal component analysis were used to identify cultivar-specific tolerance to temperatures. Based on the analysis, cultivars CZ 5225 LL and GS47R216 were identified as most sensitive and tolerant to LT, while, cultivars 45A-46 and 5115LL identified as most tolerant and sensitive to HT, respectively. The information on cultivar-specific tolerance to low or high temperatures obtained in this study would help in cultivar selection to minimize stand loss in present production areas.
Highlights
Soybean is an important oilseed crop in the US Midsouth, where an average air temperature of soybean planting dates vary from early March to late May depending upon the type of production system followed, namely, early soybean production system (ESPS) and conventional soybean production system (CSPS) [2,3].The CSPS involves May and later plantings of soybean varieties belonging to maturity group (MG)◦ C is considered ideal for germination and seedling emergence [1].Agronomy 2019, 9, 13; doi:10.3390/agronomy9010013 www.mdpi.com/journal/agronomyV-VIII, which allows rapid seed germination and emergence [4]
The experiment consisted of a collection of 64 soybean cultivars from maturity groups (MG) III, IV, and V (Table 1) that are most commonly grown in the US Midsouth and were evaluated under three different day/night temperature treatments (TTs) namely, low temperature (LT; 20/12 ◦ C), optimum temperature (OT; 30/22 ◦ C), and high temperature (HT; 40/32 ◦ C)
On an average across cultivars, the values for plant height (PH) and node number (NN) significantly increased (p < 0.001) with increasing temperatures from low to high, but leaf area (LA) was significantly reduced under LT effects with no differences were observed between OT and HT (p > 0.05)
Summary
Soybean is an important oilseed crop in the US Midsouth, where an average air temperature of soybean planting dates vary from early March to late May depending upon the type of production system followed, namely, early soybean production system (ESPS) and conventional soybean production system (CSPS) [2,3].The CSPS involves May and later plantings of soybean varieties belonging to maturity group (MG)◦ C is considered ideal for germination and seedling emergence [1].Agronomy 2019, 9, 13; doi:10.3390/agronomy9010013 www.mdpi.com/journal/agronomyV-VIII, which allows rapid seed germination and emergence [4]. The CSPS involves May and later plantings of soybean varieties belonging to maturity group (MG). Whereas ESPS involves planting early-maturing varieties, MG III and IV, from late-March to early-April [5]. Soybean acres and yields are consistently increased in the US Midsouth since the shift from CSPS to ESPS, which provides benefits of early season rainfall, avoids reproduction stage from mid-summer drought and high temperatures, prevents late-season insect-attack, and potential early harvest [1]. Farmers may risk the exposure of early-growth (seed germination and seedling emergence) of soybean to chilling injury under ESPS, leading to uneven and poor stand establishment [5]. Planting too early under EPSP and too late under CSPS could expose soybean seedling growth to both low- and high-temperatures, respectively, in the US Midsouth
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