Modeling of Shoot Elongation and Leaf Appearance in Potted Mulberry

Summary

To predict mulberry growth, modeling of shoot elongation and leaf appearance of potted mulberries was attempted. Potted mulberries were grown in temperature-controlled phytotrons. Changes in the rates of mulberry shoot elongation and leaf appearance, and the relationship between the rates and temperature were investigated. The rate of shoot elongation increased until the shoot length reached about 100cm, and became stable thereafter. The rates of both shoot elongation and leaf appearance increased with the increase in temperature from 15°C to 27°C, but not at higher temperatures. However, the rate of leaf appearance increased with the rise in temperature up to 31°C. On the basis of these results, the shoot elongation and leaf appearance of mulberry in phytotron were simulated in non -linear regression models. The relationship between the rate of shoot elongation and temperature, and the rate of leaf appearance and temperature in the model fitted to measured values very well, and that between the rate of shoot elongation and shoot length in the models tended to be in accordance with the measured values. Shoot length and leaf number predicted by the model were in concurrence with the measured values.     

Evapotranspiration Responses of Plants and Crops to Carbon Dioxide and Temperature

Summary

Atmospheric carbon dioxide (CO2) concentration has risen from about 270 mmol (CO2) mol^?1 (air) (i.e., mole fraction of dry atmospheric air basis) before 1700 to about 370 mmol mol ^?1 currently. General Circulation Models (GCM) have predicted a global temperature rise of 2.8 to 5.2°C for a doubling of CO2. This review examines evapotranspiration and water-use efficiency responses of plants to rising CO2 and climatic changes, especially temperature. Doubling of CO2 will decrease leaf stomatal conductance to water vapor about 40%. However, water use by C3 crop plants under field conditions has usually been decreased only 12% or less for two reasons. Firstly, feedbacks in the energy balance of plant foliage cause leaf temperatures to rise as stomatal conductance is decreased. Increases of leaf temperature raise the vapor pressure of water inside the leaf, which increases the leaf-to-air vapor pressure difference. This increased driving force for transpiration offsets in large part the decreased leaf conductance caused by elevated CO2. Secondly, CO2 enrichment tends to cause leaf area to increase more rapidly in many crops. This increased leaf surface area for transpiration also offsets part of the decreased stomatal conductance per unit leaf area on the whole canopy evapotranspiration, but the energy budget feedbacks are more important.

Experiments point to a yield enhancement of 30 to 35% for C3 crops for the direct effects a doubling of CO2 (without ancillary climate change). If temperature rises, this yield enhancement may be greater for vegetative growth but less for seed grain yield. Experiments on both ambient and elevated CO2 treatments in sunlit growth chambers showed that transpiration rates increased 20% when air temperature was changed from 28 to 33 °C and increased 30% when temperature was increased from 28 to 35 °C. Thus, under well-watered conditions, evapotranspiration will increase about 4 to 5% per 1°C rise in temperature.

Crop model predictions of yields of soybean and maize showed a reduction due to temperature increases by two GCM models. Under Southeastern USA conditions, doubling CO2 in the Goddard Institute for Space Studies (GISS) climate change scenario resulted in an 12% increase in yields, but yields decreased 50% in the Geophysical Fluids Dynamics Laboratory (GFDL) climate change scenario. Optimum irrigation for both models gave yield increases of about 10%. These model results illustrate the critical requirement of water for production of crops. Under rainfed conditions, crop yields could suffer tremendously if growing season precipitation is decreased, but yields could increase moderately if growing season precipitation is increased. Under the high growing season rainfall scenario (GISS), irrigation requirements for optimum soil water were increased 22%, but under the low rainfall scenario (GFDL), irrigation requirements were increased 111%.

Without the effects of climate change, rising CO2 will cause an increase in crop water-use efficiency (WUE). Most of the increases in WUE will be due to increases in dry matter, with little or no contribution from decreases in water use per unit land area. Growers could produce higher yields per unit land area with higher total production, or maintain the same total production with less land and less total water use. However, if temperatures rise, transpirational water use will increase, and WUE will decline. Higher temperatures, and especially less rainfall, would raise the irrigation requirements of crops. Competition for water resources from other uses could result in less water available for irrigation.     

The Promotive Effect of Brassinolide on Lamina Joint-Cell Elongation,Germination and Seedling Growth under Low-Temperature Stress in Rice (Oryza sativa L.)

Summary

The cell elongation-promoting activities of brassinolide (BR) and indoleacetic acid (IAA) in the lamina-inclination test using etiolated rice seedlings were compared at a low temperature. IAA promoted the lamina joint-cell elongation at 30°G, but the effect was markedly lowered with decreasing temperature and reached null at 15°C. On the other hand, BR and castasterone (CAS), a brassinosteroid, promoted this cell elongation even at 15°G. Homobrassinolide (HBR), a brassinosteroid, also promoted this cell elongation, although the activity was weak. The combination of BR and IAA synergistically promoted this cell elongation at a low temperature (15°G).

Immersion of the dry seeds in 2 X 10^-8 M BR for the first 24 h promoted the early growth of rice seedlings. This treatment also enhanced the germination rate and the growth after direct sowing in submerged paddy pots in a greenhouse or phytotron at a low temperature (15°C). Leaf spraying of BR on the rice seedlings at the 4th leaf stage increased plant height and the fresh weights of tops and roots even at a low temperature. BR sprayed on the completely expanded 4th leaves did not increase their blade length, but that sprayed on the expanding 5th and 6th leaves strikingly increased their blade length, and the effect tended to be stronger at a low temperature.

These results suggest that BR promotes cell elongation in young rice seedlings under low-temperature stress, although IAA had no such effect, and that BR may promote germination and the early growth of rice seedlings at a low temperature in direct sowing in the submerged paddy field and in the rice nursery.     

The Effect of Day to Night Temperature Variation on Leaf Development in Wheat

Summary

The rate of leaf development in wheat is related to time and temperature in units of degree-days (DD) leaf^?1 (phyllochron). Experiments were conducted in controlled environment chambers to study the effect of day to night variation in temperature on leaf development in two wheat cultivars, Penawawa and Stephens. Plants were grown at constant 20°C, and in eight day/night temperature ranges as wide as 8/32°C to 32/8°C, all with a mean temperature of 20°C. The leaf number on the main stems was counted (in Haun units) every other day, from the emergence of the 2nd leaf until the emergence of the 5th leaf. Leaf phyllochron values were derived from the inverse of the slopes of the linear regression of leaf number on DD. Phyllochron values ranged from 99 to 153 DD leaf^?1. The phyllochron values were greater when higher temperatures were imposed at night under extreme day to night temperature treatment.     

Effects of Soil Temperature on Growth and Root Function in Rice

Abstract

The objective of this study was to clarify the effects of soil temperature in the stage from late tillering to panicle initiation (SI) and during the grain-filling stage (SII) on grain setting, dry matter production, photosynthesis, non-structural carbohydrate (NSC), xylem exudation and abscisic acid (ABA) levels in rice (Oryza sativa L. cv. Koshihikari). Rice plants were exposed to four different soil temperatures during SI or SII: 17.5, 25, 31.5 and 36.5°C (ST18, ST25, ST32 and ST37, respectively). The yield, yield components, grain filling and quality in SI were negatively influenced by high soil temperature of 37°C. On the other hand, there was no significant difference in those characters among temperature treatments in SII. The root/shoot ratio was smallest in the ST37 plants in both SI and SII, mainly due to their lighter root weight. At 7 days after initiation of treatment (DAT) in both SI and SII, the photosynthetic and xylem exudation rate tended to increase slightly as soil temperature increased up to 32°C. At 21 DAT, however, the photosynthetic rate was lowest in ST37, with concurrent decrease of diffusion conductance and SPAD value. In addition, decrease of NSC concentration in stem and xylem exudation rate, and increase of ABA level in leaves and xylem exudate were observed in ST37 plants at 21 DAT. These results suggested that high soil temperature before heading especially influenced yield, grain quality and plant growth. Possible mechanisms of the effect of soil temperature are discussed.     

Effects of Low Root Temperature on Dry Matter Production and Root Water Uptake in Rice Plants

Abstract

Chilling is a major constraint in rice production in cool climates. In rice (Oryza sativa L.) plants, both the air temperature and the water (soil) temperature affect various growth processes independently, and low root zone temperature (thus, root temperature) can inhibit rice growth and yield. In this study, we investigated the effect of low root temperature on rice growth in relation to dry matter production and root water uptake. Plants were grown in hydroponic solutions at two temperatures, one equivalent to air temperature and the other 14ºC for 15 d starting 11 d after germination. Low temperature of the solution (low root temperature) inhibited dry matter production of rice plants by decreasing leaf area rather than photosynthetic rate. The response of leaf area was affected by changes in plant water status, that is relative water content (RWC) of stem was decreased by low root temperature resulting in reduced leaf area. The decrease in RWC caused by low root temperature was related to that in root hydraulic conductance (K_r). The responses of transpiration (E) and K_r to the low root temperature depended more on root surface area than on changes in hydraulic conductance per unit root surface area (Lp_r). These results suggest that dry matter production under the low root temperature condition is controlled mainly by quantitative growth parameters such as leaf area and root surface area.     

Temperature-dependent fecundity of overwintered Unaspis yanonensis (Hemiptera: Diaspididae) and use of degree-days for the prediction of first crawler

The longevity and fecundity of the overwintered arrowhead scale, Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae), was examined at constant temperatures. The total fecundity increased up to 24 °C and declined thereafter. Total fecundity reached a maximum of 260.9 eggs per female at 24 °C. Females demonstrated periodic oviposition activity but the pattern differed with temperature. The first cycle of fecundity was not significantly different between 16 and 28 °C. However, fecundity in the latter cycles, measured at rearing temperatures of 16, 20 and 32 °C, was lower than at 24 and 28 °C. The pre-oviposition period ranged from 49.0 d at 16 °C to 19.7 d at 32 °C, and was shortest (19.4 d) at 28 °C. The longevity was found to be greatest (87.3 d) at 16 °C and was as short as 48.9 d at 32 °C. Regression of the mean development rate vs. temperature provided a low-threshold temperature estimate of 8.7 °C for the pre-oviposition stage and a thermal constant of 358.4 degree days. The theoretical low threshold temperature and thermal constant applied to the calculation for the completion of the U. yanonensis pre-oviposition period predicted the appearance of first crawlers in the field.     

Carbon dioxide enrichment and temperature effects on cotton canopy photosynthesis,transpiration, and water-use efficiency

The objectives of this study were to evaluate effects of ambient and double ambient [CO₂] at a range of growing temperatures on photosynthesis, respiration, transpiration, water-use efficiency and dry matter accumulation of cotton plants (Gossypium hirsutum L., cv. DPL 50). In Experiment I, plants were grown outdoors until first bloom, then transferred into naturally lit growth chambers and grown for 22 days at 30/18°C with five CO₂ concentrations varying from 350 to 900 μl l⁻¹. In Experiment II, air temperatures were maintained at 20/12, 25/17, 30/22, and 35/27°C day/night during a 70-day experimental period with [CO₂] of 350 and 700 μl l⁻¹ at each temperature. Photosynthesis increased with [CO₂] from 350 to 700 μl l⁻¹ and with temperature. Plants grown at 35/27°C produced fewer bolls due to abscission compared with plants grown at optimum temperatures (30/20°C). At higher [CO₂], water-use efficiency increased at all temperatures due mainly to increased canopy photosynthesis but also to more limited extent to reduced canopy transpiration. Increased photosynthesis at higher [CO₂] resulted in greater dry matter accumulation at all temperatures except at 20/12°C. Respiration increased as dry matter and temperature increased. Plants grown at higher [CO₂] had less respiration per unit dry matter but more per unit area. These results indicate that future increases in [CO₂] are likely to benefit cotton production by increasing carbon assimilation under temperatures favorable for cotton growth. Reduced fruit weights at higher temperatures indicate potential negative effects on production if air temperatures increase as projected in a high-CO₂ world.     

Promotion of Seedling Growth of Seeds of Rice (Oryza sativa L. cv. Hitomebore) by Treatment with H2O2 before Sowing

Abstract

High germinability of seeds and establishment of young seedlings in rice (Oryza sativa L.) are necessary for direct seeding in paddy fields. We investigated whether germinability and seedling growth were promoted by treatment of rice seeds (cv. Hitomebore) with hydrogen peroxide solution (H₂O₂) during the imbibition for 24 h. H₂O₂ treatment with 50 mM H₂O₂ promoted seed germination, and seedling growth (shoot length, root length and shoot fresh weight) in agar culture under a low temperature condition (18°C day/14°C night). Seedling growth was promoted by H₂O₂ treatment not only under the low-temperature condition but also under a normal (23°C day/18°C night) temperature condition. Furthermore, H₂O₂ treatment promoted seedling growth under a flooding condition in a greenhouse. These results suggest that H₂O₂ treatment of rice seeds during the imbibition is advantageous for direct seeding. We discussed the relation between the promotion of the seed germinability and the seedling growth under a low-temperature condition, and the expression of some genes encoding ROS scavenger enzymes induced by H₂O₂ treatment.     

Differential sensitivity to temperature of cuphea vegetative and reproductive growth

Cuphea (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton; PSR23) is a new oilseed crop rich in medium-chain fatty acids similar to tropical palms. Agronomic studies suggest that temperature is a key determinant of cuphea seed yields. However, little is known about the growth and photosynthesis response of cuphea to temperature. The following study is the first of its kind to evaluate cuphea's growth and photosynthesis response to temperature. Cuphea was grown under day/night temperature regimes of 18/12, 24/18, and 30/24 °C and regression analysis was used to assess its responses of growth and photosynthesis and determine their optimum temperature range. Vegetative growth and leaf photosynthesis adapted well over the temperature range studied. However, reproductive growth was more sensitive showing a decline with increasing temperature. Reproductive growth rate was greatest under the lowest (18/12 °C) temperature treatment and declined by 43% at the highest growth temperatures. In contrast, vegetative growth, which was greatest under the 24/18 °C treatment, declined by just 25 and 10% at the lowest and highest temperatures, respectively. Photosynthesis acclimated to temperature by up-regulation of in vivo Rubisco activity with declining growth temperature. Maximum Rubisco activity (V_cmax) in leaves under the 18/12 °C treatment was 76% greater than that of leaves grown at 30/24 °C. Photosynthetic acclimation permitted cuphea to vegetatively grow well over a wide temperature range, but does not explain the sensitivity of reproductive growth to temperature, which will require further research to elucidate.     

Effect of temperature on germination and early growth of subterranean clover, capeweed and Wimmera ryegrass

Germination of annual pasture species was studied under controlled‐environment conditions in south‐western Australia at temperatures in the range from 4°C to 35°C. Subterranean clover (Trifolium subterraneum) and Wimmera ryegrass (Lolium rigidum) had a germination of 90% between 12°C and 29°C, whereas capeweed (Arctotheca calendula) had a high germination percentage in a much narrower temperature range with an optimum of 25°C. Growth of subterranean clover, capeweed and Wimmera ryegrass between 28 and 49 days after sowing (DAS) was also studied at two photon flux densities, 13 and 30 mol m^?2 d^?1, and at diel temperatures in the range from 15/10°C to 33/28°C. Pasture species grown at a density of 1000 plants m^?2 accumulated at least twice the amount of shoot dry matter when subjected to temperatures of 21/16°C and 27/22°C, compared with a lower temperature of 15/10°C and a higher temperature of 33/28°C. Except at the highest temperature and at high photon flux density, capeweed had lower green area indices (GAI) than the other two species at 28 DAS. Crop growth rates between 28 and 49 DAS were higher in Wimmera ryegrass than in the other two species, whereas subterranean clover had a lower relative growth rate than the other two species at all temperatures and both photon flux densities. Subterranean clover and capeweed intercepted a greater proportion of the incident radiation compared with Wimmera ryegrass. The values of radiation interception and GAI were used to estimate the number of DAS to reach 75% radiation interception [f_(0·75)]. The number of days to reach f_(0·75) decreased with increasing temperature from 15/10°C to reach a minimum at 27/22°C. The time taken to achieve f_(0·75) was always shorter by about 10 d when the photon flux density was 30 mol m^?2 d^?1 in the autumn compared with 13 mol m^?2 d^?1 in the winter. These results are discussed in relation to the early growth of annual pasture in the field.     

Influence of heat stress on dry matter production and photo-assimilate partitioning by four potato clones

Partitioning patterns of¹⁴C labeled assimilates were studied to determine their relationship to dry matter accumulation and distribution in four potato clones (Desiree, DTO-28, LT-1 and Russet Burbank). Plants placed in growth chambers at 35/25 C day/night temperature and 12-hour photo-period two weeks after tuber initiation were compared with plants grown continuously at 25/12 C. Two weeks after temperature treatments were begun, the most recently expanded leaf was labeled with¹⁴CO₂ for 30 minutes, and plants were harvested 20 hours or 15 days later. High temperature reduced total dry matter production and altered dry matter distribution in favor of vines at the expense of tubers. Partitioning of¹⁴C assimilates generally followed the pattern of dry matter distribution. Potato clones exhibited variation in¹⁴C assimilate export from labeled leaves and in partitioning to vines and tubers. Assimilate partitioning to tubers was not consistently higher in clones considered heat tolerant.     

Effects of temperature on growth and photosynthesis in the seedling stage of the sheath blight-resistant rice genotype 32R

The 32R rice genotype is resistant to sheath blight disease (ShB), with a high-yield potential. We examined effects of temperature on the plant responses of 32R in comparison with those of the ShB-susceptible rice genotype (29S) and Nipponbare (Nb, a Japonica standard cultivar). The seedlings at the 4th leaf stage of rice genotypes were exposed to 14/14, 19/14, 25/20, 31/26, 37/32 and 37/37 °C (day/night) for 5, 10 and 15 days. The dry weight, leaf area, photosynthesis, contents of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and chlorophyll contents were examined. The dry weight showed lower in 32R than in 29S and Nb at a low temperature, and total dry weight correlated strongly with root dry weight and leaf area. The relative growth rate (RGR) correlated strongly with the net assimilation rate (NAR). Rubisco, chlorophyll contents and the photosynthetic rates were limited at a low temperature and showed lower in 32R than in 29S and Nb. The strong correlations between Rubisco and the rates of maximum photosynthesis and initial slope were found in 32R, but not found in 29S and Nb. In addition, RGR and NAR of 32R correlated positively with Rubisco. These suggest that 32R contains traits of cold-sensitive genotypes that are related to limiting Rubisco at a low temperature, thus diminishing photosynthesis and limiting plant growth. Differences of growth among 32R, 29S and Nb were discussed in the relation of genotypes.     

Cuban brown snail,Zachrysia provisoria (Gastropoda): Damage potential and control

The snail Zachrysia provisoria (Pfeiffer) is poorly known in Florida, USA, where it predominately is viewed as a pest of ornamental plants. I evaluated its host plant relationships, foliage consumption potential, and susceptibility to several molluscicides. Many of the potential hosts, especially common ornamental plants that are planted densely as ground cover and might be expected to provide a favorable environment for snails, are not suitable for growth of young snails. Older snails, though displaying some ability to feed and damage hosts unsuitable for growth of young snails, displayed similar patterns of acceptance and growth. Several weeds were favorable for growth, suggesting that untended environments could lead to snail problems in adjacent ornamental plantings. The effect of plant condition (age) on snail feeding preference was assessed by measuring leaf consumption by snails presented simultaneously with young (green, located apically) and senescent (yellowing or yellow, located basally) leaves of a single plant species. From preferred host plants, snails chose young leaf tissue, but from less preferred plants they consumed senescent tissue. Foliage consumption potential was assessed using romaine lettuce at two constant temperatures, 24 and 32 °C. Foliage consumption increased with age (wet weight) at both 24 and 32 °C; however, the rate of consumption was higher at the lower temperature. At 24 °C, mean peak consumption was about 40 cm² of leaf area or 12 g wet weight/day. At the less favorable high temperature of 32 °C, mean peak consumption was reduced by about 50%, to a mean of only 20 cm² or 6 g wet weight/day. Relative consumption rate (cm² or g foliage/g snail) diminished with age (wet weight) of the snails. Several molluscicide-containing baits were assessed. Metaldehyde-based baits induced mortality most quickly, followed by iron-based baits. A boric acid-based bait was slowest, requiring 12 days for the induction of significant levels of mortality. All baits significantly suppressed feeding, however, sometimes even in the absence of mortality.     

Effects of atmospheric CO2 concentration and defoliation on the growth of Themeda triandra

The effects of elevated atmospheric carbon dioxide (CO₂) concentration (700 μmol mol^?1) on defoliated (three clippings at 3‐week intervals) and undefoliated plants were determined for the C₄ grass Themeda triandra, Forsk. The elevated CO₂ concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO₂ concentration treatment. The primary effect of the elevated CO₂ concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down‐regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO₂ concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO₂ concentration treatment were lost following a final 3‐week reversion to ambient CO₂ concentration, but occurred in plants exposed to the elevated CO₂ concentration for the final 3‐week period only. In conclusion, elevated atmospheric CO₂ concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO₂ responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation.     

不同角度倒伏对寒地水稻的影响

在大田栽培条件下,为探索和了解寒地水稻不同角度倒伏的变化特征,以寒地水稻垦稻12号为试验材料,比较了不同角度倒伏的寒地水稻植株干物质和形态变化规律,探索了不同倒伏角度水稻的空间部位分布动态变化情况。结果表明:倒伏前期水稻茎鞘干重表现为0°>45°>90°,节间重与节间长度的比值表现为0°<45°<90°。在倒伏前、后两个时期,水稻倒1、2叶片长度以及重量均以0°倒伏的作用强度最明显;而在株高和重心高度上均表现为0°>45°>90°,而在穗长与株高比值上的变化则正好与其相反。综合分析表明,0°倒伏水稻上部空间承受的压力要明显高于其它倒伏角度的水稻。     

Effect of incandescent and fluorescent lighting used in photoperiod extension on the vegetative growth and floral development of four lines of pigeonpea

The effects of light quality, as used in photoperiod extension, on vegetative growth and floral development of pigeonpea [Cajanus cajan (L.) Millsp.] were studied using three photoperiod-insensitive lines, QPL2, Prabhat, and Hunt, and one photoperiod-sensitive line, Royes. Plants were grown in controlled-environment cabinets under day/night temperature regimes of 24/16°C (low) and 28/24°C (high) for 72 days after emergence (DAE). The five light treatments consisted of 12 and 16-h photoperiods and a 12-h photoperiod extended to 16 h with low-intensity lighting from either incandescent (I), fluorescent (F), or incandescent plus fluorescent (I+F) lamps.Little genetic variation occurred in vegetative response (main stem length and node number, leaf area and shoot dry weight) to extension light source. Response varied with temperature, plant age and growth stage. Main stem node appearance and stem extension tended to decline following floral initiation (FI), whereas leaf area and shoot dry weight accumulation increased rapidly after 35 or 42 DAE, irrespective of whether plants were vegetative or floral. Plants were larger under the high-temperature regime. Temperature altered plant response to extension light source. I-extension promoted growth under both temperature regimes, whilst I+F promoted growth under high temperatures but was unexpectedly inhibitory under low. Under high temperatures F extension was inhibitory prior to FI, but promoted later growth during floral bud development (FBD). Under low temperatures, F-extension was not inhibitory during the pre-initiation phase.The four genotypes differed in their floral response to extension light source, the effect on initiation and development of floral primordia varying dependent upon temperature. Low temperatures resulted in sensitivity to extension light source, delaying FI and FBD. In Royes, failure to initiate under low temperatures was associated with small plant size (≤3.5 g shoot dry weight). High temperatures tended to negate the delaying effects of extension light source, but resulted in photoperiod sensitivity, delaying FI in the early-flowering lines QPL-2 and Prabhat. Under high temperatures, Royes was insensitive (FI and FBD) to extensions containing incandescent light (I, I+F). Under high temperatures, time of flowering was least affected by incandescent extensions (I, I+F), and most by F-extension, which delayed FBD in all lines. Under low temperatures, I+F extensions resulted in the greatest variation in flowering time.It was concluded that where heterogeneity exists in floral response to the intensity and/or quality of light, use of artificial lighting to select for photoperiod sensitivity may lead to misclassification.     

GA3 and Proline Promote Germination of Wheat Seeds by Stimulating α-Amylase at Unfavorable Temperatures

abstract

The effects of various constant temperatures (4, 9, 14, 19, 24, 29, 34, and 38°C) on the germination of winter wheat seed ( Triticum aestivum L. cv. ‘Koyuki’) in a dark condition were studied. The maximum germination percentage was 98% at 24°C. The speed of germination was fastest at 29°G. These results indicate that the most suitable temperature for germination was in the range of 24 to 29°G. α-Amylase expression during germination was also high at higher temperature, and maximum expression occurred at 29°C, although a high temperature of 38°C prevented the synthesis of α-amylase. The close correlation between germination and α-amylase activity at various temperatures indicates that α-amylase is an essential factor for the temperature-dependent germination of wheat seed. In contrast, accumulation of proline increased at a lower temperature, and was the highest at 4°G. We also studied the effects of gibberellin (GA₃) and proline, a compatible osmotica in alleviating the effect of low and high temperature stresses. Pre-soaking treatment with GA3 and proline was effective in promoting germination and increasing α-amylase expression at a low (4°C) and high (38°C) temperature. These results suggest that GA₃ and proline exhibit positive effects on stress alleviation through the stimulation of α-amylase expression.     

Varietal Difference in Early Vegetative Growth during Seedling Stage in Soybean

Abstract

Rapid development after emergence is important for seedling establishment and early vegetative growth, especially at a low planting density or inferior environmental conditions. This study was conducted to understand the varietal difference in the growth parameters during the seedling stage in soybean. Twenty-seven soybean varieties originating from six countries were examined in 2009 and 2010. The pots were arranged in a completely random block design with 5 replications (10 pots per variety), and the seedlings were sampled at 14 and 28 days after sowing (DAS). The shoot dry weight at 14 and 28 DAS was highly correlated with seed size, cotyledon digestion, and leaf area. However, no positive correlation was found between shoot dry weight and photosynthetic rate at 28 DAS. Chamame, a Japanese cultivar, with the largest seed size grew rapidly, and showed the heaviest shoot dry weight, greatest cotyledon digestion, fast leaf expansion and high photosynthetic rate. However, Moyashimame, a medium-seed-size cultivar, also grew rapidly with a high photosynthetic rate. Some varieties such as Tachinagaha (Japan), Hefeng (China), Parana and Pérola (Brazil), had a large or medium seed size, and high photosynthetic rate but showed a relatively small leaf area and light shoot dry weight. These results suggested that big seeds with rapid cotyledon digestion developed a wider leaf area and therefore large dry matter production, indicating that the conversion of stored energy was more important than the leaf photosynthetic activity for early growth.     

Internodal elongation: A potential screening technique for heat tolerance in potato

Summary In pot culture experiments over 2 consecutive years, 20 potato genotypes of varying heat tolerance were grown under long day conditions and heat stressed by being exposed to high (38 °C/21 °C mean day/night) temperature. The percent increase in mean internode length of heat stressed plants over those grown at normal temperatue (25°C/16°C day/night) was correlated with the percent tuber dry matter yield of the heat stressed plants (r=0.618, P=0.01). In the same 20 genotypes, grown under short day conditions at normal temperature, the fraction of leaf bud cuttings exposed to high night temperature (23°C) that produced tuber initials correlated with the percentage increase in internode elongation in stem cuttings exposed to 25°C compared with those exposed to 15°C (r=0.680. P=0.01). Thus the relative changes in internode elongation are related to thermal tolerance, and it is suggested that this can be used as a selection criterion for heat tolerance.