Negative Effects Of High Temperature Research Articles

INFLUENCE OF HIGH TEMPERATURES AT BLOOMING TIME ON POLLEN PRODUCTION AND FRUIT SET OF PEACH 'MACIEL' AND 'GRANADA'

Regions under subtropical conditions commonly have temperature fluctuations and at late winter time the occurrence of temperatures above 25°C followed by less than 10°C is not rare. This is probably one of the causes for production inconsistency over the years. Several field and laboratory tests were conducted using two peach cultivars, 'Granada' and 'Maciel', aiming to study the effect of high temperature (≥25°C) at blooming period. In vitro pollen viability at different temperatures was tested using a culture medium prepared with 1% agar plus 10% sugar in distilled water. Pollen production per anther was also evaluated. In field experiments, branches of these two cultivars were submitted to temperatures 2 to 8°C above field temperatures, using plastic bags or transparent bottles (pet) or covering a whole plant with a portable greenhouse. The observed parameters were: in vitro pollen viability, pollen production per anther (total and normal pollen grains), length of pistils and fruit set. In laboratory tests, pollen germination was lower at 32°C, than at 24 or 28°C for both cultivars. Higher temperatures did not significantly influence length of pistils, probably because the field temperatures at the tested years were already high. Total pollen production did not differ among tested temperatures, however percentage of normal pollen grains was significantly lower in 'Granada' at higher temperatures and did not differ for 'Maciel'. The same was true for fruit set. The conclusion is that the negative effect of high temperatures at blooming time is larger for 'Granada' than for 'Maciel'.

Exogenous Application of Putrescine Ameliorates the Effect of High Temperature in Gossypium hirsutum L. Flowers and Fruit Development

AbstractPolyamines have been shown to stimulate fruit set and the initial phase of fruit development in several crops. The effect of exogenous application of putrescine on ovary development and seed set of cotton under high temperature stress was investigated under controlled environmental conditions. Putrescine was applied to floral buds of cotton, 24 h prior to anthesis, and caused a significant increase in putrescine content of cotton ovaries collected at anthesis compared with the control treatment. However, there was no increase in spermidine and spermine. High temperature (38 °C) significantly decreased the spermidine content of cotton ovaries in both years of the study compared with the untreated control (30 °C). Spermine was significantly decreased in the high temperature treatment the first year of the study; however, this result was not consistent for the second year. Ovarian putrescine concentration was not affected by the high temperature treatment. Increased temperatures in this study decreased seed set in cotton flowers; however, exogenous application of putrescine ameliorated the negative effect of high temperature on seed set, as expressed by the number of seeds per cotton boll. This was evident in both years of the study. Exogenous application of Putrescine increased the level of putrescine in cotton flowers, which was associated with increased seed set despite the negative effect of increased temperature.

Climatic Change and Agronomic Performance of Hard Red Spring Wheat from 1950 to 2007

Increasing temperatures are a threat to hard red spring wheat (Triticum aestivum L.) production in the northern Great Plains and may impact objectives for breeding programs. Weather data and agronomic performance of experimental lines and a check cultivar ‘Thatcher’ were compiled for six sites in Montana for 1950 to 2007. Mean annual temperature increased significantly at five sites. March temperature increased significantly at all sites, and planting date has become significantly earlier at a rate of 0.24 d yr−1. Grain yield of Thatcher increased significantly at a rate of 23.5 kg ha−1 yr−1. July temperatures increased significantly at two sites. July temperatures showed a significant negative correlation with grain yield at three sites and with grain volume weight at three sites. Nursery means over years as adjusted for Thatcher was used as a measure of genetic change and showed significantly increased grain yield and significantly earlier heading date. Our results suggest that earlier planting due to warmer spring temperatures has helped to alleviate negative effects of high temperatures during grain filling periods. Genetic changes in breeding materials have also contributed to increased yield potential, partially due to earlier heading and avoidance of July heat. Projection of increasing temperatures suggests the need for management and breeding strategies to insure productivity of hard red spring wheat in the northern Great Plains.

Effect of acclimatization to low temperature and reduced light on the response of reef corals to elevated temperature

This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient (27.7°C) temperature, under shaded (352 μmol photons m−2 s−1) or ambient (554 μmol photons m−2 s−1) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons m−2 s−1). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (Fv/Fm), and growth, and the effect of the subsequent treatment was assessed as Fv/Fm and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even con-generic taxa differ in this capacity, which could affect coral community structure.

Review of the Consequences and Control of High Air Temperatures in Intensive Livestock Buildings

The behaviour and physiology of intensively housed animals will be negatively affected when the environmental temperature is above their thermo-neutral zone (TNZ). It is likely that production efficiency, welfare, health and reproductive capacity of the animals will be compromised. Traditional technologies, such as the use of different cooling systems and better building design, can be used to alleviate the negative effects of high temperatures on animals. However, there are real opportunities to further develop climate control technologies and create intelligent environmental control systems that will be able to predict and therefore control both the responses of animals and the buildings in relation to selected control interventions.

Carrot Seed Germination at High Temperature: Effect of Genotype and Association with Ethylene Production

Carrot (Daucus carota L.) seed germination may be erratic or reduced under high temperatures (above 35 °C). Even in tropical genotypes (tolerant to high temperatures during crop development), the negative effects of high temperatures on carrot stand establishment have been observed, especially during summer. The objectives of this study were to characterize commercial carrot cultivars and accession lines for their ability to germinate at high temperature and determine the ethylene production during imbibition at high temperature. Seeds from 34 commercial cultivars and 125 carrot accessions from the North Central Regional Plant Introduction Station were germinated at 25 °C (optimal) and 35 ± 0.5 °C (high) in constant light. Ethylene production during seed imbibition at high temperature was evaluated in some genotypes. Many of the commercial cultivars had reduced germination at 35 °C. ‘XPC-3617’, ‘Alvorada’, ‘Brasilia’, and ‘Esplanada’ had the greatest germination at 35 °C. A greater number of accessions germinated at 35 °C than did the commercial genotypes. The accession PI 319858 germinated 95% at both temperatures and was considered thermotolerant. Six accessions (Ames 7665, Ames 7698, Ames 25031, PI 167082, PI 294637, and PI 319858) germinated above 80% at 35 °C and were also identified as potential sources of thermotolerance. Fifteen other accessions (Ames 7694, Ames 25031, Ames 25036, Ames 25049, Ames 25705, PI 167082, PI 179687, PI 180834, PI 261782, PI 269486, PI 273658, PI 277710, PI 288242, PI 294637, and PI 319858) had thermotolerance ratios of T35/T25 0.85 or greater (where T35 = germination at 35 °C and T25 = germination at 25 °C) and were identified for further testing. The identified thermotolerant genotypes might be useful for carrot seed germination mechanism studies as well as for breeding programs. Ethylene production during seed germination at high temperature was greater in thermotolerant genotypes than in thermosensitive genotypes. High correlations were observed between first germination count at 35 °C and ethylene production, total germination at 35 °C and ethylene production, and thermotolerance ratio and ethylene production.

The combined effects of temperature and GnRHa treatment on the final stages of sexual maturation in Atlantic salmon (Salmo salar L.) females

Atlantic salmon (Salmo salar L.) females (2 SW), maturing for the first time, were reared under one of three temperature regimes (high: 14.3 +/- 0.5 degrees C; natural: 10.6 +/- 1.0 degrees C; and cold: 6.9 +/- 1.0 degrees C) in combination with one of two experimental treatments; an injection of GnRH analogue (GnRHa) contained in biodegradable microspheres, or a sham injection (microspheres only). The six experimental groups were then reared under simulated natural photoperiod for 4 weeks. Blood samples were drawn for analysis of plasma steroid levels and the fish were inspected for ovulation weekly. Batches of stripped eggs were incubated in triplicate incubators in raceways until the eyed stage. Treatment with GnRHa resulted in a substantial advancement and synchronization of ovulation at all temperatures, while exposure to cold water also appeared to advance ovulation slightly. While 75% (warm and cold) to 90% (natural) of GnRHa fish ovulated during the 4-week trial, only 30% of sham-treated females exposed to cold water, and none of the sham-treated fish held at higher temperatures, ovulated during this period. Survival rates of embryos to the eyed-stage were significantly higher for broodstock exposed to cold water. Plasma levels of testosterone (T), 17beta-oestradiol (E2), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20betaP) were all significantly affected by treatment with GnRHa and, to a lesser extent, temperature. The efficiency of GnRHa in counteracting the negative effects of high temperature on ovulation and the associated changes in circulating sex steroids suggest that temperature inhibition operates at least in part at the brain or pituitary.

The Impact of Altitude and Simulated Herbivory on the Growth and Carbohydrate Storage of Petasites albus

We tested the hypothesis that higher respiratory losses caused by higher temperatures in the lowlands, compared to montane sites, prevent growth of the montane hemicryptophyte Petasites albus (Asteraceae). In addition, we tested whether increased levels of herbivory enhanced carbon losses at lower elevations. Rhizomes of Petasites albus were transplanted to a montane and a lowland site. In the subsequent three growing seasons the plants were artificially defoliated to simulate mollusc herbivory. Whereas there were no altitudinal differences in the leaf number per plant, the leaf area was higher at the montane site. At the montane site, the leaf number and leaf area decreased with increasing damage, and the rhizome dry weight in the third year was much higher in the undamaged plants. In contrast, fructan concentrations in the rhizomes that were harvested at the end and at the beginning of the growing seasons were generally higher at the lowland site. No clear defoliation effects were observed on most harvest dates. The results indicate that the lower altitudinal limit of Petasites albus cannot be explained by the negative effects of higher temperatures or more leaf damage by herbivores in the lowlands, either alone or in combination. An explanation will require consideration of other site factors such as competition and possibly interactions with herbivory and carbohydrate storage.

Effects of elevated temperature and carbon dioxide on seed‐set and yield of kidney bean (Phaseolus vulgaris L.)

AbstractIt is important to quantify and understand the consequences of elevated temperature and carbon dioxide (CO2) on reproductive processes and yield to develop suitable agronomic or genetic management for future climates. The objectives of this research work were (a) to quantify the effects of elevated temperature and CO2 on photosynthesis, pollen production, pollen viability, seed‐set, seed number, seeds per pod, seed size, seed yield and dry matter production of kidney bean and (b) to determine if deleterious effects of high temperature on reproductive processes and yield could be compensated by enhanced photosynthesis at elevated CO2 levels. Red kidney bean cv. Montcalm was grown in controlled environments at day/night temperatures ranging from 28/18 to 40/30 °C under ambient (350 µmol mol−1) or elevated (700 µmol mol−1) CO2 levels. There were strong negative relations between temperature over a range of 28/18–40/30 °C and seed‐set (slope, − 6.5% °C−1) and seed number per pod (− 0.34 °C−1) under both ambient and elevated CO2 levels. Exposure to temperature > 28/18 °C also reduced photosynthesis (− 0.3 and − 0.9 µmol m−2 s−1 °C−1), seed number (− 2.3 and − 3.3 °C−1) and seed yield (− 1.1 and − 1.5 g plant−1 °C−1), at both the CO2 levels (ambient and elevated, respectively). Reduced seed‐set and seed number at high temperatures was primarily owing to decreased pollen production and pollen viability. Elevated CO2 did not affect seed size but temperature > 31/21 °C linearly reduced seed size by 0.07 g °C−1. Elevated CO2 increased photosynthesis and seed yield by approximately 50 and 24%, respectively. There was no beneficial interaction of CO2 and temperature, and CO2 enrichment did not offset the negative effects of high temperatures on reproductive processes and yield. In conclusion, even with beneficial effects of CO2 enrichment, yield losses owing to high temperature (> 34/24 °C) are likely to occur, particularly if high temperatures coincide with sensitive stages of reproductive development.

Growth of the black-lip pearl oyster, Pinctada margaritifera, at nine culture sites of French Polynesia: synthesis of several sampling designs conducted between 1994 and 1999

Between 1994 and 1999, several sampling designs were used to measure the growth of the black-lip pearl oyster, Pinctada margaritifera var. cumingi at different sites in French Polynesia. Using a common statistical method, growth data were analysed for nine sites and showed significant geographic variability. Parameters of the Von Bertalanffy model, fitted on the nine data sets, ranged from 147 to 186.5 mm for the H ∞ parameter and from 0.42 to 0.58 year –1 for the k parameter. The φ parameter (combination of H ∞ and k) provided a ranking classification of growth in these nine sites: growth was low in closed atoll lagoons, such as Takapoto, whereas the island lagoons and ocean habitat supported a very promising shell growth. Calculated on the basis of these models, two parameters of interest for pearl farming were computed: 1) the time for pearl oysters to reach a size of 100 mm (size at which they are suitable for nucleus implantation), which ranged from 21 to 26 months, and 2) the annual shell growth increment at this size (correlated to the rate of nacreous deposition on the pearl), which varied from 19.7 to 31.8 mm·year –1. The combination of these two sets of results demonstrated that the time necessary to produce a comparable pearl varied significantly according to the site. Several hypotheses to explain the differences observed in the growth of P. margaritifera in these nine sites are proposed. The most reasonable would appear to be: 1) the negative effect of high temperature (> 30°C), and 2) the degree of water renewal and food supply around the bivalve. Although this paper demonstrated significant variability in growth performance in the nine investigated sites, further investigations are needed, especially concerning the flesh growth rate. Indeed, this highly relevant parameter, which reflects both bivalve health and the suitability of farming sites, has received very little attention to date.

Effects of exposure to high ambient temperature and dietary protein level on performance of multiparous lactating sows.

Fifty-nine multiparous Large White x Landrace sows were used to determine the effects of high ambient temperature and level of dietary heat increment on lactation and reproductive performance. During a 28-d lactation and the 14-d postweaning period, ambient temperature was maintained constant at 20 or 29 degrees C. Experimental diets fed during lactation were a control diet (NP; 17.6% crude protein) and two low-protein diets obtained by reduction of CP level (LP; 14.2% CP) and both reduction of CP and addition of 4% fat (LPF; 15.2% CP); the NE:ME ratio was 74.3, 75.6, and 75.8% for NP, LP, and LPF diets, respectively. All diets provided 0.82 g of digestible lysine/MJ of NE, and ratios between essential amino acids and lysine were above recommendations. During the ad libitum period (i.e., between d 7 and 27 of lactation), ADFI and NE intake decreased, respectively, from 7.63 to 4.22 kg and 82.0 to 43.3 MJ of NE when the temperature increased from 20 to 29 degrees C. Exposure to 29 degrees C reduced litter BW gain (2,152 vs 2,914 g/d) and increased lactation BW loss (34 vs 16 kg) but increased postweaning BW gain (2 vs - 4 kg). Expressed per kilogram of feed intake, water intake increased from 4.0 to 7.5 L between 20 and 29 degrees C. Compared with the NP diet, low-CP diets (LP or LPF) maintained performance and reduced total N excretion (-22.5%) in lactating sows at thermoneutrality and attenuated the negative effects of high temperature on NE intake and BW loss (40.9 vs 47.9 MJ of NE/d and 41 vs 30 kg for NP and LP + LPF diets, respectively). Temperature and diet composition did not affect the reproductive performances, and the mean weaning-to-estrus interval was 4.9 d. The respiratory rate and skin, udder, and rectal temperatures increased markedly at 29 degrees C (105 vs 33 breaths per min and 37.8 vs 36.1 degrees C, 38.9 vs 38.2 degrees C, and 39.5 vs 38.8 degrees C, respectively) without any effect of diet. In conclusion, low heat increment diets (i.e., with reduced CP/NE ratio) did not affect lactation performance of sows at thermoneutrality and attenuated the effects of high ambient temperature on energy intake and BW loss. At any ambient temperature, N excretion can be markedly reduced.

Is there a higher risk for herbivore outhreaks after cold mast years? An analysis of two plant/herbivore series from southern Norway

Historical data on two plant-herbivore interactions from southern Norway were used to test the hypothesis that the degree of herbivore outbreaks in post-mast years is negatively related to summer temperatures in the mast year, because plants are more depressed after a high seed production if temperatures and thus the photosynthetic activity is low. The plant species were the sessile oak Quercus petraea and the bilberry Vaceinium myrtillus. For the former species post-mast years were identified from reports given by the local forest authorities for the period 1930–48, and from acorn export curves for the period 1949–98, For the latter species, post-mast years were identified mainly from bilberry export curves for the period 1920–31, from game reports for the period 1932–78. and from diary notes for the period 1979–87. The herbivore species used were the green oak leaf roller moth Tortrix viridana and the capercaillie Tetrao urogallus. Eight moth outbreaks on oak forests were reported by the forest authorities in the period 1930–98, and they all started in a post-mast year of the sessile oak. There were however also eleven post-mast years without moth outbreaks. According to game reports, observations and autumn counts, all increases in the autumn population size of capercaillie during 1920 88 occurred in or after a year with high bilberry production. Among i8 post-mast years, there were seven with strong increase, seven with slight or moderate increase, and four with no increase. For both herbivore species, post-mast years with marked population increases had significantly lower summer temperatures in the preceding (mast) year than had post-mast years with no or slight increases. For moth populations there also was a negative effect of high temperatures in April, possibly because moth eggs tend to hatch too early relative lo budburst if spring temperatures are high. For the capercaillie, high amount of precipitation in June – July seemed to have some negative impact on the autumn population sizes, as also found in previous studies.

Induction of Thermotolerance inTrichogramma brassicae(Hymenoptera: Trichogrammatidae)

Temperature variations recorded during releases of the parasitoid Trichogramma brassicae Bezden ko used against the European corn borer, Ostrinia nubilalis Hubner (Lepidoptera), Mere simulated in the laboratory by applying single or double heat shock at 35 or 44°C for 6 h during the white pupal stage. Several biological characteristics were studied in the treated generation and its progeny. Induction of heat shock proteins was checked. Large (70-84-88-92 kDa) and small (25-26-28-29-32 kDa) heat shock proteins accumulated and persisted at least for 1 d in treated pupae. Consistent with the biologically negative effects of high temperatures recorded in the field, we observed that increased pupal mortality, decreased fecundity, and male sterility resulted from a 44°C treatment during the pupal susceptible period. A 35°C pretreatment had a protective effect with respect to a 2nd shock at 44°C, and this thermotolerance could be attributed to the persistence of heat shock proteins in the treated pupae during the period following the primary heat shock.

An analysis of the balance between root and shoot activity in Lolium perenne cv. Melvina. Effects of CO2 concentration and air temperature.

This study investigated the mechanisms which control the partitioning between roots and shoots in plants subjected to changes in environment. Two types of analyses were used: firstly, an examination of the cost and revenue associated with investment in different plant parts, and secondly, a test of the principle of functional equilibrium between roots and shoots, i.e. whether root dry matter × root specific activity balances shoot dry matter × shoot specific activity. Measurements were made on individual plants of Lolium perenne in sunlit controlled environments, grown from germination to canopy closure under optimal nitrogen supply. At the final harvest, increased air temperature (+ 4 °C above ambient) reduced whole-plant dry matter by 12% relative to the control, whereas elevated CO., mole fraction (700 μmol mol -1 ) led to a 38 % gain. The combined treatment yielded an intermediate result (+ 19%). Plants grown at + 4°C maintained balanced activity between roots and shoots throughout the experimental period, irrespective of CO2 concentration. This required enhanced allocation to roots in young plants to compensate for a strong negative effect of higher temperature on root specific activity, which suggests that plants conserve balanced activity by adjusting dry matter partitioning. The extra cost involved with the adjustment at +4°C significantly enhanced the cost:revenue ratio of plant investment. In ambient temperature, the balance between roots and shoots departed from equilibrium, slightly at ambient but substantially at elevated CO2 : the plants accumulated excess carbon relative to nitrogen, and this imbalance increased with plant age. At elevated CO2 , the cost: revenue ratio increased in young plants but this was later reversed owing to loss of root specific activity, which explains the gradually declining CO2 , stimulation with time. The strategies in equilibrating root and shoot functioning observed in the different treatments are discussed in the light of whole plant performance.

Effects of temperature rise and increase in CO2 concentration on simulated wheat yields in Europe

A crop-growth-simulation model based on SUCROS87 was used to study effects of temperature rise and increase of atmospheric CO2 concentration on wheat yields in several regions in Europe. The model simulated potential and water-limited crop production (growth with ample supply of nutrients and in the absence of damage by pests, diseases and weeds). Historic daily weather data from 13 sites in Western Europe were used as starting point. For potential production (optimal water) a 3 °C temperature rise led to a yield decline due to a shortening of the growing period on all locations. Doubling of the CO2 concentration caused an increase in yield of 40% due to higher assimilation rates. It was found that effects of higher temperature and higher CO2 concentration were nearly additive and the combination of both led to a yield increase of 1-2 ton ha-1. A very small CO2-temperature interaction was found: the effect of doubled CO2 concentration on crop yield was larger at higher temperatures. The inter-annual yield variability was hardly affected. When water was limiting crop-production effects of temperature rise and higher CO2 levels were different than for the potential production. Rise in temperature led to a smaller yield reduction, doubled CO2 concentration to a larger yield increase and combination of both led to a large yield increase (3 ton ha-1) in comparison with yields simulated for the present situation. Both rise in temperature and increase in the CO2 concentration reduced water requirements of the crop. Water shortages became smaller, leading to a reduction in inter-annual variability. It is concluded that when no major changes in precipitation pattern occur a climate change will not affect wheat yields since negative effects of higher temperatures are compensated by positive effects of CO2 enrichment.

Growth and Topological Changes of Citrus limon (L.) Burm. f. `Eureka' in Response to High Temperatures and Elevated Atmospheric Carbon Dioxide

Growth and topological indices of `Eureka' lemon were measured after 6 months in well-watered and well-fertilized conditions and factorial combinations of moderate (29/21C day/night) or high (42/32C day/night) temperatures and ambient (350 to 380 μmol·mol) or elevated (constant 680 μmol·mol-1) CO2. In high temperatures, plants were smaller and had higher levels of leaf chlorophyll a than in moderate temperatures. Moreover, plants in high temperatures and elevated CO2 had about 15 % higher levels of leaf chlorophyll a than those in high temperatures and ambient CO2. In high temperatures, plant growth in elevated CO2 was about 87% more than in ambient CO2. Thus, high CO2 reduced the negative effect of high temperature on shoot growth. In moderate temperatures, plant growth in elevated CO2 was only about 21% more than in ambient CO2. Irrespective of temperature treatments, shoot branch architecture in elevated CO2 was more hierarchical than those in ambient CO2. Specific shoot extension, a topological measure of branch frequency, was not affected by elevated CO2 in moderate temperatures, but was increased by elevated CO2 enrichment in high temperatures-an indication of decreased branch frequency and increased apical dominance. In moderate temperatures, plants in elevated CO2 had fibrous root branch patterns that were less hierarchical than at ambient CO2. The lengths of exterior and interior fibrous roots between branch points and the length of second-degree adventitious lateral branches were increased >50% by high temperatures compared with moderate temperatures. Root length between branch points was not affected by CO2 levels.

Interactions of CO2, temperature and management practices: simulations with a modified version of CERES-Wheat.

A new growth subroutine was developed for CERES-Wheat, a computer model of wheat (Triticum aestivum) growth and development. The new subroutine simulates canopy photosynthetic response to CO2 concentrations and light levels, and includes the effects of temperature on canopy light-use efficiency. Its performance was compared to the original CERES-Wheat V-2 10 in 30 different cases. Biomass and yield predictions of the two models were well correlated (correlation coefficient r > 0.95). As an application, summer growth of spring wheat was simulated at one site. Modeled crop responses to higher mean temperatures, different amounts of minimum and maximum warming, and doubled CO2 concentrations were compared to observations. The importance of irrigation and nitrogen fertilization in modulating the wheat crop climatic responses were also analyzed. Specifically, in agreement with observations, rainfed crops were found to be more sensitive to CO2 increases than irrigated ones. On the other hand, low nitrogen applications depressed the ability of the wheat crop to respond positively to CO2 increases. In general, the positive effects of high CO2 on grain yield were found to be almost completely counterbalanced by the negative effects of high temperatures. Depending on how temperature minima and maxima were increased, yield changes averaged across management practices ranged from -4% to 8%.

Comparison of two models for the prediction of rest completion in peaches

Phenological and climatic data were collected from nectarine orchards containing the cultivars ‘Sunlite’, ‘Flavortop’ and ‘Fantasia’, growing in six climatically divergent areas in the Western Cape, South Africa. Shoots were forced at 25°C and bud volumes measured in order to develop an index of when the winter chilling requirement for each cultivar in each area had been satisfied. Flower bud break gave the only consistent indication of when the chilling requirement had been satisifed and 10% flower bud break after 14 days at 25°C was adopted as the end of rest index. The ‘dynamic’ rest completion prediction model was considerably more accurate than the currently used ‘Utah’ model, for estimating the rest requirement of the nectarine cultivars ‘Sunlite’, ‘Flavortop’ and ‘Fantasia’. The ‘dynamic’ model not only takes into account the positive effect of cool temperatures and negative effect of high temperatures on rest completion that the ‘Utah’ model does, but also the positive effect of moderate temperatures and the fact that chilling negation is subject to time constraints. The cultivars tested required about 33, 41 and 41 ‘dynamic’ portions of chilling respectively, followed by an average of 2000 ± 1067 degree growing hours above a 10°C base temperature in order to reach full bloom in spring. Vegetative bud break was enhanced in the colder locations, while reproductive development was better in the warmer locations.

Enhanced Celery Germination at Stress Temperature via Solid Matrix Priming

To alleviate high-temperature-induced reductions in seed germination, emergence, and seedling uniformity in celery (Apium graveolens L.), seeds were primed via solid matrix priming (SMP); 0.5 g celery seeds was incubated at 15C with 10 g calcined clay and 2 ml water. After 2 days, 1, 2, 3, or 4 ml water or 1% NaOCl solution was added and seeds were kept for 2, 4, 6, 8, 10, 12, and 14 additional days. The germination percentage and coefficient of germination velocity (COV) were calculated for each treatment at 15 and 30C. The seeds primed with NaOCl gained significantly less moisture after 8 days of priming than those treated with water, regardless of the volume added. Germination of nonprimed seeds was 83% and 2% at 15 and 30C, respectively. Final germination at 30C increased to >80% when seeds were primed with 3 or 4 ml NaOCl solution or 3 ml water for >10 days. SMP treatment significantly reduced the negative effect of high temperature on celery seed germination.

ENHANCED GERMINATION OF CELERY AT STRESS TEMPERATURE VIA SOLID MATRIX PRIMING

The high temperature severely reduces seed germination, emergence, and seedling uniformity in celery (Apium graveolens L.). Celery seeds were primed via solid matrix priming (SMP) using water or 1% sodium hypochlorite (NaOCl) solution at 1, 2, 3 or 4 ml rate for 2, 4, 6, 8, 10, 12 and 14 days. Moisture content of the seeds was calculated for each priming treatment and time interval. After priming, the seeds were dried back to the original dry weight. The germination percentage was calculated for each treatment at two different temperatures (15 and 30C). The seed primed with NaOCl gained significantly less moisture during priming than the water treatment. Seeds primed with NaOCl had significantly greater germination at both 15 and 30C, compared to seeds primed with water. The germination percentage of non-primed seeds was 83% and 2% at 15C and 30C, respectively. The final germination percentage at 30C was increase to 85% when the seeds were primed with 3 ml of NaOCl for 14 days. The combination of SMP with NaOCl significantly reduced the negative effect of high temperature on celery seed germination.