Drought and heat stresses are the major abiotic stress factors detrimental to maize ( Zea mays L.) production. Much attention has been directed toward plant responses to heat or drought stress. However, maize reproductive stage responses to combined heat and drought remain less explored. Therefore, this study aimed to quantify the impact of optimum daytime (30°C, control) and warmer daytime temperatures (35°C, heat stress) on pollen germination, morpho‐physiology, and yield potential using two maize genotypes (“Mo17” and “B73”) under contrasting soil moisture content, that is, 100% and 40% irrigation during flowering. Pollen germination of both genotypes decreased under combined stresses (42%), followed by heat stress (30%) and drought stress (19%). Stomatal conductance and transpiration were comparable between control and heat stress but significantly decreased under combined stresses (83% and 72%) and drought stress (52% and 47%) compared with the control. Genotype “Mo17” reduced its green leaf area to minimize the water loss, which appears to be one of the adaptive strategies of “Mo17” under stress conditions. The leaf reflectance of both genotypes varied across treatments. Vegetation indices associated with pigments (chlorophyll index of green, chlorophyll index of red edge, and carotenoid index) and plant health (normalized difference red‐edge index) were found to be highly sensitive to drought and combined stressors than heat stress. Combined drought and heat stresses caused a significant reduction in yield and yield components in both Mo17 (49%) and B73 (86%) genotypes. The harvest index of genotype “B73” was extremely low, indicating poor partitioning efficiency. At least when it comes to “B73,” the cause of yield reduction appears to be the result of reduced sink number rather than the pollen and source size. To the best of our awareness, this is the first study that showed how the leaf‐level spectra, yield, and quality parameters respond to the short duration of independent and combined stresses during flowering in inbred maize. Further studies are required to validate the responses of potential traits involving diverse maize genotypes under field conditions. This study suggests the need to develop maize with improved tolerance to combined stresses to sustain production under increasing temperatures and low rainfall conditions.
Drought stress during the reproductive stage and declining soybean yield potential raise concerns about yield loss and economic return. In this study, ten cultivars were characterized for 20 traits to identify reproductive stage (R1–R6) drought-tolerant soybean. Drought stress resulted in a marked reduction (17%) in pollen germination. The reduced stomatal conductance coupled with high canopy temperature resulted in reduced seed number (45%) and seed weight (35%). Drought stress followed by rehydration increased the hundred seed weight at the compensation of seed number. Further, soybean oil decreased, protein increased, and cultivars responded differently under drought compared to control. In general, cultivars with high tolerance scores for yield displayed lower tolerance scores for quality content and vice versa. Among ten cultivars, LS5009XS and G4620RX showed maximum stress tolerance scores for seed number and seed weight. The observed variability in leaf reflectance properties and their relationship with physiological or yield components suggested that leaf-level sensing information can be used for differentiating drought-sensitive soybean cultivars from tolerant ones. The study led to the identification of drought-resilient cultivars/promising traits which can be exploited in breeding to develop multi-stress tolerant cultivars.
Soybean [Glycine max (L.) Merr.)] production trends have increased throughout the past century due to its versatile use in food, feed, and fuel industries. The selection of soybean cultivars with higher yields coupled with consumer-preferred seed quality has become a priority to sustain economic advantage. In this study, eighteen popular soybean cultivars from different maturity groups (MG III to V) were phenotyped for yield and quality traits under optimum water and nutrient conditions. Significant phenotypic variability was observed for days to flowering, yield, and seed quality traits. The late flowering soybean cultivars (MG V) recorded 14% lower seed weight than the early flowering (MG IV). Under optimum growing conditions, protein content increased with the MGs, but oil content decreased. Further, significant negative correlations between protein and yield, oil, and sucrose were observed. In contrast, the oil content was positively correlated with yield. Cultivars 539-T3 and GT-477CR2 were classified as high-yielding short-duration soybean cultivars. Based on the cultivar performance index, MS 4616 RXT and 7547XT were found to have a combination of desirable industry traits such as high protein, and oil content with high yield compared to other cultivars. The current research provides prospective benchmark seed weight and quality parameters under sunlit and temperature conditions with optimum water and nutrient conditions for many soybean cultivars grown in the US Mid-South. Furthermore, it can assist growers and breeders in selecting soybean cultivars with high protein and oil specific to their regional demand.
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