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In this study, we employed chlorophyll a fluorescence technique, to indicate plant health and status in response to changing day lengths (photoperiods) and temperatures in soybean early and late maturity groups. Chlorophyll a fluorescence study indicates changes in light reactions in photosystem II. Experiments were performed for 3-day lengths (12.5, 13.5, and 14.5 h) and five temperatures (22/14°C, 26/18°C, 30/22°C, 34/26°C, and 40/32°C), respectively. The I-P phase declined for changing day lengths. Active reaction centers decreased at long day length for maturity group III. We observed that low temperatures impacted the acceptor side of photosystem II and partially impacted electron transport toward the photosystem I end electron acceptor. Results emphasized that higher temperatures (40/32°C) triggered damage at the oxygen-evolving complex and decreased electron transport and photosynthesis. We studied specific leaf areas and aboveground mass. Aboveground parameters were consistent with the fluorescence study. Chlorophyll a fluorescence can be used as a potential technique for high-throughput phenotyping methods. The traits selected in the study proved to be possible indicators to provide information on the health status of various maturity groups under changing temperatures and day lengths. These traits can also be deciding criteria for breeding programs to develop inbreed soybean lines for stress tolerance and sensitivity based on latitudinal variations. [ABSTRACT FROM AUTHOR]

On a global scale, soybean (Glycine max (L.) Merr.) is cultivated across a wide range of environmental conditions, characterized by variable temperatures and day lengths. It is important to gather information about different maturity group's phenology and growth patterns to enhance agricultural practices and develop various soybean crop models. We conducted two experiments focusing on soybean maturity groups, commonly used cultivars for early and late maturity groups (one cultivar for each maturity group), one with varying day/night temperatures (22/14, 26/18, 30/22, 34/26, and 40/32°C) under a constant day length of 12.5/11.5 hours. Second, we investigated day lengths of 12.0, 12.5, 13.0, 13.5, 14.0, and 14.5 hours under constant temperature (26°C). We examined various morpho-phenological traits, including plant height, branch number per plant, vegetative development rate, and days to the first flower. Long-day lengths were found to increase the number of branches per plant, whereas shorter-day lengths led to earlier flowering in the cultivars utilized for the experiment. The duration until the first flower was prolonged under lower temperatures and longer day lengths. As a result, understanding the impacts of temperatures and day lengths and their interactions during the leaf, branch, and flowering stages will significantly contribute to improving seed production in future environmental conditions. Furthermore, the insights gained from this study will play an important role in enhancing soybean breeding programs and improving soybean crop models. • Temperature and daylength are major environmental factors deciding soybean growth. • Low temperature and long daylength prolonged the vegetative stage of soybean plants. • Soybean early maturity groups were less sensitive to daylengths for first flowering. • Soybean late maturity groups were more susceptible to temperature and daylength. • Study helps selecting maturity groups, cultivars according to climatic conditions. [ABSTRACT FROM AUTHOR]

Extreme temperatures are considered one of the main constraints that limit the growth and development of rice. We elucidated the root and shoot developmental plasticity of 64 rice genotypes during early seedling establishment, using the sunlit plant growth chambers at 22/14 (low), 30/22 (optimum), and 38/30 °C (high) day/night temperatures. Low temperature severely inhibited 23 traits, such as shoot (68%), root (57%), and physiological (35%) attributes. On the contrary, the high temperature positively affected most of the shoot (48%) and root (31%) traits, except root diameter and root/shoot ratio, compared with the optimum. Alternatively, leaf chlorophyll fluorescence-associated parameters declined under low (34%) and high (8%) temperatures. A weak correlation between cumulative high-temperature response index (CHTRI) and cumulative low-temperature response index (CLTRI) indicates the operation of different low- and high-temperature tolerance mechanisms at the early seedling stage. Groups of distinct rice genotypes associated with low or high-temperature tolerance were selected based on CHTRI and CLTRI. The genotypes that commonly performed well under low and high temperatures (IR65600-81-5-2-3, CT18593-1-7-2-2-5, RU1504114, RU1504122, Bowman, and INIA Tacuari) will be valuable genetic resources for breeders in developing early-season high- and low-temperature-tolerant genotypes for a broad range of both tropical and temperate rice-growing environments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]