Environmental stress during soybean [Glycine max (L.) Merr.] seed fill can alter the chemical composition of the seed and reduce yield, viability, and vigor. The effect of drought and high air temperature (AT) on soybean seed protein and oil contents have not been reported. The objective of this study was to characterize the protein and oil contents and fatty acid composition of soybean seeds after exposure to drought and high AT during seed fill. Experiments were conducted during two years, in which three drought‐stress levels were maintained throughout seed fill. In Experiment I, “Gnome” soybeans were grown at daytime AT of 20 and 26°C, and in Experiment II “Hodgson 78” were grown at 27, 29, 33, and 35°C. Across experiments, severe drought increased protein content by 4.4 percentage points, while oil content decreased by 2.9 percentage points. As drought stress increased, measured by accumulating stress degree days, protein content increased linearly and oil content decreased linearly at each AT. Seeds from plants exposed to 35°C during seed fill contained 4.0 percentage points more protein and 2.6 percentage points less oil than those exposed to 29°C when averaged across drought stress levels. Drought had little effect on the fatty acid composition of the oil, but high AT reduced the proportion of the polyunsaturated components.
High diurnal temperatures often affect development of soybean [Glycine max (L.) Merr.], but little is known about the relative influence of high day and night temperatures on the chemical composition of the seed. This study was conducted to determine the effects of combinations of high day and night temperatures during flowering and pod set (R1-R5), seed fill and maturation (R5-R8), and continuously during the reproductive period (R1-R8) on soybean seed oil, protein, and fatty acid composition. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30~ were imposed on the soybean cultivar Gnome 85 in growth chambers. The day/night temperature combinations during R1-R5 had little effect on the oil and protein concentration and the fatty acid composition of seed produced. As mean daily temperature increased from 25 (30/20) to 33 (35/30)~ during R5-R8 and 25 (30/20) to 33 (35/30)~ during R1-R8, and oil concentration decreased and protein concentration increased. Increased day temperature during R5-R8 and R1-R8, averaged across the two night temperatures, increased oleic acid and decreased linoleic and linolenic acids. When night temperature was increased at 30~ day temperature during R5-R8 and R1-R8, oleic acid decreased and linoleic acid increased. When night temperature was increased at 35~ day temperature during R1-R8, oleic acid increased, and linoleic and linolenic acids decreased. These results indicate the importance of high day and night temperatures during seed fill and maturation in the oil, protein, and fatty acid composition of soybean seed. JAOCS 73, 733-737 (1996).
maximum grain size. A growth chamber study by Badu-Apraku et al. (1983) shows a more dramatic yield loss The average temperature in the U.S. Corn Belt during the grainassociated with high temperatures during the period of filling period of maize (Zea mays L.) is above optimum for maximum grain yield. The objectives of this study were to determine the effects grain filling . They observed a 42% loss in grain weight of an extended period of high temperature during grain filling on per plant when day/night temperature from 18 d postkernel growth, composition, and starch metabolism of seven maize silking to maturity was increased from 25/15 to 35/15ЊC, inbreds. Plants were exposed to heat stress (33.5/25؇C) or control (25/ a6 ЊC rise in average daily temperature. 20؇C) day/night temperature treatments in a greenhouse from 15 dThe interaction of heat stress with other environmenafter pollination (DAP) until maturity, and the experiment was contal factors in the field, such as drought stress, makes it ducted in triplicate over time. Root zone temperature was maintained difficult to study the effect of high temperature on maize at 25/20؇C in both treatments. No significant interaction occurred yield in isolation. Furthermore, it may be difficult to between genotype and temperature treatments for nine grain traits. separate the effects of heat stress occurring during grain Heat stress lengthened the duration of grain filling on a heat unit filling from a previously occurring heat stress. The use (HU) basis, but an overcompensatory reduction in kernel growth rate per HU resulted in an average mature kernel dry weight loss of 7% of controlled environments makes it possible to study (P ϭ 0.06). Proportionally similar reductions occurred for starch, more precisely how high temperature treatment affects protein, and oil contents of the kernel. Heat stress also reduced kernel maize grain filling. However, controlled-environment density. A survey of 11 enzymes of sugar and starch metabolism studies should strive to mirror conditions in the field as extracted from developing endosperm revealed that ADPglucose pyclosely as possible. As described below, conditions of rophosphorylase, glucokinase, sucrose synthase, and soluble starch root temperature and photyosynthetically active radiasynthase were most sensitive to the high temperature treatment. Howtion (PAR) intensity can differ between the field and ever, upon adjusting enzyme activities with measured temperature controlled environment and have been shown to be coefficients (i.e., Q 10 ), only ADPglucose pyrophosphorylase exhibited important factors that help determine how plants rereduced activity. Results indicate that chronic heat stress during grain spond to high temperature.filling moderately restrains seed storage processes and select enzymes of starch metabolism to similar degrees across multiple maize inbreds.
Water and high air-temperature (AT) stresses that occur during soybean (Glycine max (L.) Merr.) seed fill greatly reduce seed yield, but their effects on seed germination and vigor are less clear. The objective of this study was to determine the effect of water stress at optimum and high AT during seed fill on soybean seed yield and individual seed weight, and the subsequent germination and vigor of the seed. At daytime ATs of 27 and 35 °C in 1985 and 29 and 33 °C in 1986, control, moderate, and severe water-stress treatments were imposed by differential irrigation throughout seed fill on greenhouse-grown plants. Water stress intensity, measured by accumulating stress degree days (SDD) during seed fill, increased linearly as the volume of irrigation water declined. The weight and number of seed produced by each plant, and individual seed weight, declined linearly as SDDs accumulated at each AT. Water stress at optimum ATs reduced seed number more than individual seed weight, but water stress at high ATs reduced individual seed weight more than seed number. Water or high AT stress caused fewer larger seed and more small seed to be produced. The germination percentage and vigor of the harvested seeds was reduced by water stress and high ATs, but by a smaller proportion than yield or seed number. Individual seed weight, germination, and seedling growth rate were strongly correlated when reduced by water and high AT stress. Severe stress during seed fill caused soybean plants to exceed their capacity to buffer seed number, shifting seed weight distributions towards a larger proportion of small seed, resulting in poor seed lot germination and vigor. Key words: Soybean, germination, vigor, drought, high temperature, heat stress
Growth temperature influences the seed yield of soybean [Glycine max (L.) Merr.]. Most studies have concentrated on the effects of concomitant increases in day/night temperature during the entire life cycle of soybean. A better understanding of the influence of combinations of high day and night temperature imposed during different reproductive growth phases on soybean seed yield would be beneficial in identifying yield limiting factors. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30°C were imposed during flowering and pod set (R1-R5), seed fill and maturation (R5-R8), and during the entire reproductive period (R1-R8). Increases in day'temperature resulted in decreased seed formation when plants were exposed during flowering and pod set and decreased seed growth when exposed during flowering and pod set or seed fill. Seed growth reductions in plants exposed to the high day temperature were accompanied by decreased photosynthetic rates. The largest yield reduction in this study was 27% and occurred when 35°C occurred for 10 h per day from flowering to maturity. No significant losses in yield occurred at high night temperature at any reproductive growth phase. The only significant interaction between day and night temperature for the yield components was for seed weight per plant during flowering and pod set. Night temperature stress did not occur at 30°C and a night temperature of 20°C did not reduce the yield loss from daytime high temperature stress. This study suggests that soybean seed yield reductions from high temperatures are primarily a response to day temperature and moderate to high night temperatures have a small affect on soybean seed yield components.
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