Cool Night Temperatures Research Articles

Forecasting wheat productivity in Punjab, India: A weather-based model approach using detrended data and regression analysis

Weather-based models were developed to forecast the wheat productivity of three districts in Punjab (India) could accurately predict wheat yields two and a half months before the crop harvest. The trends in weather parameters were identified using Mann-Kendal, Sen’s Slope and Pettitt’s test.The logistic model was declared best among linear and non-linear models to remove the effect of technological factors over time. The detrended data was used for forecasting wheat productivity based on fourteen weeks of weather data of the vegetative period. The stepwise regression technique for detrended wheat productivity on weather indices revealed model II best for Amritsar, Ludhiana and Patiala districts, explaining 60%, 67% and 52% variation in the detrended wheat productivity and had root mean square percentage error 8.57%, 6.93% and 6.20% respectively. The model concluded that warm maximum and cool night temperatures of the wheat growing season will increase detrended wheat productivity, whereas an increase in rainfall and relative humidity in the morning will decrease detrended wheat productivity and hence the production.

Impact of contrasting soils in a high-altitude vineyard of <i>Vitis vinifera</i> L. cv. Malbec: root morphology and distribution, vegetative and reproductive expressions, and berry skin phenolics

The high-altitude viticulture of Mendoza is being increasingly recognised among the top wine regions worldwide. High levels of solar ultraviolet-B (UV-B) radiation, alluvial heterogeneous soils and cool night temperatures are major influences on Vitis vinifera L. phenotypic characteristics, especially on Malbec, Argentina’s emblematic grapevine variety. In the present work, the effect of intra-vineyard contrasting soil depth on Malbec was evaluated in a high-altitude vineyard (1450 m a.s.l.), over two growing seasons for physiological traits and over three vintages for yield components and berry skin phenolic compounds. The experiment was carried out in two parcels of shallow (SS) and deep (DS) soils, with different physico-chemical characteristics, and submitted to equal irrigation and crop management. Results showed that root depth was not limited by any soil physical constraints and fine roots (< 1 mm) were patchily distributed in sites with higher contents of silt, clay and organic matter in SS. Higher root quantity in SS was related to lower vegetative and reproductive expressions, shorter ripening period and reduced berry size and fruit yield when compared to DS. When SS plants experienced mild water stress (ΨS, stem water potential, between -6 and -9 bar) increments of anthocyanins, total polyphenols and antioxidant capacity in berry skins were observed. However, when SS plants reached ΨS ≤ -10 bar, physiological harm occurred. The results presented contribute to understanding the effects of soil type on Malbec vines during different seasonal environmental conditions, especially in stressful situations, such as those expected by climate change scenarios.

Transient daily heat stress during the early reproductive phase disrupts pod and seed development in Brassica napus L.

AbstractTransient daily heat stress during flowering of canola (Brassica napus L.) as a result of global warming is an increasing threat to grain production in this important oilseed crop. We investigated the intensity and duration of transient daily heat stress treatment at different stages of reproductive development in three B. napus genotypes under controlled environment conditions. Heat stress treatments during the week before first open flower on the main stem (S0) or during the first week (S1) or second week (S2) following first open flower greatly reduced pod number and seed yield on the main stem. Heat stress treatment during the third week (S3), fourth week (S4), or fifth week (S5) reduced seed yield more on the branches and less on the main stem as time progressed. Pod number and seed yield were reduced by moderate heat stress (TC2; 32°C/22°C) and high heat stress (TC3; 35°C/25°C), compared with the control (TC1, 25°C/15°C). Each duration of heat stress treatment (3, 5 or 7 days) caused the same reduction in pod number and seed per pod on the main stem. Leaf stomatal conductance, leaf chlorophyll index, plant height, and dry weight of above‐ground biomass increased from TC1 to TC3, which indicates that heat stress in the absence of drought stress does not inhibit vegetative growth. Cool night temperatures (15°C) resulted in recovery of pod number and seed yield after moderate (32°C) but not high (35°C) daily transient heat stress. The range of genotype responses to heat stress was greater under TC2 than under TC3. This research brings forward the critical period for heat stress sensitivity in B. napus to one week before first open flower and defines the conditions for controlled environment screening for heat tolerance in B. napus.

Drought and heat waves associated with climate change affect performance of the potato aphid Macrosiphum euphorbiae

The combined effect of drought and heat waves on insect-plant interactions is complex and not fully understood. Insects may indirectly benefit from water-deficit stress through increased plant nitrogen levels. Heat stress may have a direct negative effect, yet insect performance may be improved when day-time heat is followed by cooler night temperatures. We show that moderate water-deficit stress (25–30% pot capacity) and high day-night temperatures (30/20 °C) affected Macrosiphum euphorbiae on potato (Solanum tuberosum) differently than their interactions. Water stress lowered stomatal conductance, and both water and heat stress reduced leaf area. The effect of water stress on nymphal and adult survival depended on temperature. Water stress added to reduced nymphal survival at high but not current (25/15 °C) day-night temperatures. Adult survival at high temperatures was reduced only when combined with water stress. Water stress and high temperatures independently but not interactively reduced the number of daily offspring. Moderate water stress when combined with high temperatures had a negative bottom-up effect on aphid survival even though lower night temperatures aided in the recovery from direct heat stress. Our study illustrates the importance of combining multiple stressors to better understand their impact on insect-plant interactions in the context of climate change.

Physiological effects of environmentally relevant, multi-day thermal stress on wild juvenile Atlantic salmon (Salmo salar)

The frequency of extreme thermal events in temperate freshwater systems is expected to increase alongside global surface temperature. The Miramichi River, located in eastern Canada, is a prominent Atlantic salmon (Salmo salar) river where water temperatures can exceed the proposed upper thermal limit for the species (~27°C). Current legislation closes the river to recreational angling when water temperatures exceed 20°C for two consecutive nights. We aimed to examine how natural thermal variation, representative of extreme high thermal events, affected the thermal tolerance and physiology of wild, juvenile Atlantic salmon. We acclimated fish to four thermal cycles, characteristic of real-world thermal conditions while varying daily thermal minima (16°C, 18°C, 20°C or 22°C) and diel thermal fluctuation (e.g. Δ5°C-Δ9°C). In each cycling condition, we assessed the role that thermal minima played on the acute thermal tolerance (critical thermal maximum, (CTMax)), physiological (e.g. heat shock protein 70 (HSP70), ubiquitin) and energetic (e.g. hepatic glycogen, blood glucose and lactate) status of juvenile Atlantic salmon throughout repeated thermal cycles. Exposure to 16-21°C significantly increased CTMax (+0.9°C) compared to a stable acclimation temperature (16°C), as did exposure to diel thermal fluctuations of 18-27°C, 20-27°C and 22-27°C, yet repeated exposure provided no further increases in acute thermal tolerance. In comparison to the reference condition (16-21°C), consecutive days of high temperature cycling with different thermal minima resulted in significant increases in HSP70 and ubiquitin, a significant decrease in liver glycogen, and no significant cumulative effect on either blood glucose or lactate. However, comparison between thermally taxed treatments suggested the diel thermal minima had little influence on the physiological or energetic response of juvenile salmon, despite the variable thermal cycling condition. Our results suggest that relatively cooler night temperatures in the summer months may play a limited role in mitigating physiological stress throughout warm diel cycle events.

Study on Climatic Variation and Its Effect on Vegetable Type Soybean Genotypes at Khumaltar, Lalitpur in the Last Ten Years

Soybean (Glycine max L. Merril) is widely grown in the mid hills as intercrop with maize or in paddy bunds, while it is gaining popularity as sole crop in terai and inner terai. Mean temperature at Khumaltar during soybean growing period was mostly fluctuating; but we observed an increasing trend in temperature. Amount of rainfall was not changed dramatically but number of rainy days was decreased during study period. Rainfall during germination time increase soil moisture which also increase germination and found higher early stand. Days from sowing to 50% flowering and 90% maturity were short in the case of higher minimum temperature and low rainfall. Among the genotypes, AGS-377, AGS-378, AGS-379 and Tarkari Bhattmas-1 were more sensitive. However, seed yield decreased in the case of higher temperatures and low rainfall. Cool night temperatures and high moisture increased disease incidence in soybean which, eventually reduced yield. In last three years, plant suffered from moisture stress during early vegetative stage and high moisture during late vegetative stage which reduced seed yield and seed weight. In conclusion, we found that genotypes like AGS- 360, Sathiya and Tarkari Bhatmas-1 are very sensitive to climatic variation.

Genotypic diversity of phenolic compounds and antioxidant capacity of Chinese dwarf cherry (Cerasus humilis (Bge.) Sok.) in China

Nutritional properties, phenolic compound contents, and antioxidant activity of Chinese dwarf cherry (Cerasus humilis (Bge.) Sok.) were investigated in 13 genotypes from Changping District of Beijing (CPBJ). In addition, four common genotypes grown in Shangyi County of Hebei Province (SYHB) were also studied to illustrate the plasticity of a given genotype in response to growth locations. A large genotypic diversity was observed in most of the assessed quality parameters and these quality parameters were also significantly affected by growth locations. Ascorbic acid value varied from 16.3 to 83.2mg 100g−1 FW in CPBJ, and from 83.4 to 84.8mg 100g−1 FW in SYHB. The highest amounts of soluble solid content (19.7%), total titratable acid (1.81%), total phenols (1899mg 100g−1 FW), total flavonoid (1861mg 100g−1 FW), procyanidin (1082mg 100g−1 FW), and total anthocyanin (39.3mg 100g−1 FW) were observed in fruits grown in SYHB. For the same genotypes, these chemical attributes were higher in fruits produced in SYHB than in CPBJ, due to consequence of the different environmental stimuli such as long days, cool night temperatures and more ultraviolet rays. High positive correlations were observed between phenolic compound contents and antioxidant activity. The results indicated that there was great future potential in biodiversity, nutritive and health care research in the investigated Chinese dwarf cherry species.

Response of diverse groups of sorghum [Sorghum bicolor(L.) Moench] genotypes to low temperature stress at anthesis

Rapid productivity increases has not been realized in winter/post-rainy/rabi sorghum, an important food crop in the semi-arid tropical regions of India. The crop is dominated with varieties as poor seed set due to susceptibility to cold stress is noticed in the hybrids. Hence, before initiation of breeding program to bring in tolerance to cold stress, diverse group of breeding material that included 8 varieties, 7 maintainer lines, 5 restorer lines and a hybrid were screened for tolerance to cold stress in two dates of sowing for pollen viability and germinability apart from other agronomic traits. Date of sowing significantly influenced pollen germinability and the influence of the cooler night temperatures was more than the genetic background. In contrast, pollen viability had less phenotypic plasticity and highly heritable. The loss of grain yield (open panicle grain yield-selfed panicle grain yield) was about 5g/panicle in varieties while it was 1.9g/panicle in restorer lines and about 5.7g/panicle in B-lines. The loss in grain yield was highest in the hybrid at about 22.9g. Higher grain yields can be attained in the hybrid with improvement in the pollen viability and germinability. The germinability percentage was positively associated with selfed panicle weight, grain yield and harvest index while the viability percentage did not show such association. The germinability percentage was more linearly related in R lines followed by B lines and varieties.

Warm-night temperature delays spike emergence and alters carbon pool metabolism in the stem and leaves of Phalaenopsis aphroide

Different night temperature treatments have been adopted for spike emergence in Phalaenopsis. The aim of this research was to study the dawn-dusk carbohydrate and organic acid levels responding to warm- (28°C day/28°C night, spike inhibitory) and cool-night (28°C day/20°C night, spike inducing) temperatures for six weeks with respect to different ages of leaves, including the new and not fully expanded 1st leaf (L1), the new and fully expanded 2nd leaf (L2), the older 5th leaf (L5) and the stem, the locus of spiking, and the dawn-dusk oscillations of metabolites associated with spiking. The results showed that L2 exhibited the maximum amplitude of nocturnal malate accumulation and daytime starch deposition on both treatments. Compared with the control, the warm-night treatment dramatically reduced the soluble sugar concentration, particularly the hexose levels in L2 and L5. However, in the stem, the sucrose concentration after warm-night treatment was significantly higher than that of the control at dawn and dusk. We deduce that the potential role of sucrose in the stem is to sustain the viability of the dormant spike bud. The occurrence of a large amount of soluble sugars in the L5 of the control implies that the breaking of bud dormancy may rely on the supply of sugars from the older leaves. The warm-night treatment significantly increased the citrate concentration in all leaves at dawn, implying that citrate might be playing a crucial role in protecting the leaves from warm-night stress.

DETERMINING THE OPTIMAL NIGHTTIME AIR TEMPERATURE FOR PHALAENOPSIS DURING THE VEGETATIVE STAGE

Daytime air temperatures above 26 degrees C inhibit flower initiation of Phalaenopsis regardless of the nighttime air temperature. This opens possibilities for energy saving by lowering the nighttime air temperature during the vegetative growth phase. As chilling injury can occur after a few hours exposure to cool temperature conditions, growers prefer to cultivate Phalaenopsis at daily temperatures between 25 and 30 degrees C. A better understanding of the low night temperature effects on the photosynthetic physiology of Phalaenopsis would improve production of these orchids in terms of greenhouse temperature control and energy use. Therefore, the Phalaenopsis hybrid 'Hercules' was subjected to nighttime air temperatures of 27.0, 24.0, 21.1, 18.0, 15.4 and 12.8 degrees C, while during the day temperatures of about 27.5 degrees C were maintained. Photoperiod was set to 9 h with non-saturating white fluorescent light (217.3 +/- 2.8 mu mol PAR m(-2) s(-1)). The chlorophyll fluorescence temperature response curves revealed a significant reduction of the photochemical quenching (qP) and quantum efficiency of PSII electron transport (Phi(PSII)) when plants were exposed to night temperatures below 21.1 degrees C, but maximum quantum yield of PSII photochemistry (F-v/F-m) suggested no PSII damage for these night temperatures. Early morning determined leaf acidity, which can be used as a measure of nocturnal malic acid production, and leaf water potential were lowest at night temperatures of 21.1 and 24.0 degrees C. However, maximum net CO2 uptake in the late night (2 h before daytime) was observed between 15.4 and 21.1 degrees C. Furthermore, PSII photochemistry required only 5 h for full recovery of all night temperatures imposed. Our results suggest that Phalaenopsis can tolerate relatively cool night temperatures during the vegetative growth stage.

A new method to determine the energy saving night temperature for vegetative growth of Phalaenopsis

Knowledge of the energy saving night temperature (i.e. a relatively cool night temperature without affecting photosynthetic activity and physiology) and a better understanding of low night temperature effects on the photosynthetic physiology of Phalaenopsis would improve their production in terms of greenhouse temperature control and energy use. Therefore, Phalaenopsis‘Hercules’ was subjected to day temperatures of 27.5°C and night temperatures of 27.0°C, 24.2°C, 21.2°C, 18.3°C, 15.3°C or 12.3°C in a growth chamber. A new tool for the determination of the energy saving night temperature range was developed based on temperature response curves of leaf net CO2 exchange, chlorophyll fluorescence, organic acid content and carbohydrate concentrations. The newly developed method was validated during a complete vegetative cultivation in a greenhouse environment with eight Phalaenopsis hybrids (i.e. ‘Boston’, ‘Bristol’, ‘Chalk Dust', ‘Fire Fly’, ‘Lennestadt’, ‘Liverpool’, ‘Precious’, ‘Vivaldi’) and day/night temperature set points of 28/28°C, 29/23°C and 29/17°C. Temperature response curves revealed an overall energy saving night temperature range for nocturnal CO2 uptake, carbohydrate metabolism, organic acid accumulation and photosystem II (PSII) photochemistry of 17.1°C to 19.9°C for Phalaenopsis‘Hercules’. At the lower end of this energy saving night temperature range, a high malate-to-citrate ratio switched towards a low ratio and this transition seemed to alleviate effects of night chilling induced photoinhibition. At night temperatures of 24°C or higher, the degradation of starch, glucose and fructose indicated an increased respiratory CO2 production. During the greenhouse validation experiment, the differences between the eight Phalaenopsis hybrids with regard to their response to the warm day/cool night temperature regimes were remarkably large. In general, the day/night temperature of 29/17°C led to a significantly lower biomass accumulation and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28°C and 29/23°C. During week 25 of the cultivation period, plants matured and flower initiation steeply increased for all hybrids and in each day/night temperature regime. Before week 25, early spiking was only sufficiently suppressed in the 29/23°C and 29/17°C temperature regimes for three hybrids (‘Boston’, ‘Bristol’ and ‘Lennestadt’) but not in the other five hybrids. Although a considerable biochemical flexibility was demonstrated for Phalaenopsis‘Hercules’, inhibition of flowering after exposure to a combination of warm days and cool nights appeared to be largely hybrid dependent.

Low Night Temperature Increases Ovary Size in Sweet Pepper Cultivars

Cool night temperatures have been reported to induce ovary swelling and consequent fruit deformation in bell pepper (Capsicum annuum L.), resulting in unmarketable fruit. This response is a serious limitation to the success of winter production systems for bell pepper. Limited work has been done with other types of sweet pepper, so it is unknown how universal this response is. Furthermore, most prior work has examined effects on ovary diameter only, and there is limited characterization of other ovary traits in response to cool night temperature. The objectives of the present study were to determine the effects of low night temperature on ovary characteristics in different sweet pepper cultivars and to determine the parts of the ovary that are most affected by these factors. Three types of sweet pepper (bell, long-fruited, and cherry) were exposed to 22/20 or 22/12 °C day:night temperatures and flowers at anthesis were continuously harvested throughout the experiments. Ovary fresh weight (FW), diameter, and length across all types (and cultivars within type) were greater under 22/12 °C compared with 22/20 °C. The increase in ovary FW was the result of increases in both ovary wall and placenta FW. In general, all cultivars exhibited increases in ovary size under 12 °C compared with 20 °C night temperature. Differences in ovary FW resulting from night temperature became more pronounced with time. These results indicate that low night temperature effects on ovary swelling may be a universal response among sweet pepper types. Three to 4 weeks are required for maximum swelling response, suggesting that flower buds must be exposed to low night temperatures within the first week after flower bud initiation, because previous work found that flower bud initiation in bell pepper takes ≈4 weeks. However, the duration of low night temperatures necessary for this response remains unknown.

Utilization of Latent Heat Storage Unit for Comfort Ventilation of Buildings in Hot and Dry Climates

In hot and dry climatic conditions of South Asia, summer night temperatures are low, and phase change material (PCM) based heat storage technique could be used as heat sink to reduce ambient air temperature during hot day times, as an alternate of current ventilation techniques for the building sector. This can help in reducing electricity consumption and consequently reducing green house gas emissions. This study presents the analysis of PCM storage unit using cooler night temperatures for charging of storage material and later acting as a heat sink for hot ambient air during day time in hot and dry climatic conditions. The influence of air flow rates and melting point of PCM on the availability of comfort temperatures at storage unit outlet has been studied. The results clearly indicate the feasibility of PCM storage unit as a heat sink to keep ambient air within comfort limits during the hot day time in summer season. When the PCM melting temperature is equal to the comfort temperature of the hottest summer month, the storage unit performance is maximized for all the months during the summer season.

Low night temperature acclimation of Phalaenopsis

The capability of Phalaenopsis to acclimate its photosynthetic capacity and metabolic activity to cool night temperature conditions is crucial for improving orchid production in terms of efficient greenhouse heating. The extent to which Phalaenopsis possesses acclimation potential and the mechanistic background of the metabolic processes involved, have, however, not been studied before. Plants were subjected to a direct and gradual shift from a day to night temperature regime of 28/28-28/16°C, the cold stress and cold acclimation treatment, respectively. In comparison with the cold stress treatment, the cold acclimation treatment led to a higher malate accumulation and a reduction in leaf net CO(2) uptake. Consistently, the contribution of respiratory CO(2) recycling to nocturnal malate synthesis was calculated to be 23.5 and 47.0% for the cold stress and cold acclimation treatment, respectively. Moreover, the lower levels of starch measured in the cold acclimated leaves confirmed the suggested enhanced respiratory CO(2) recycling, implying that Phalaenopsis CAM operation evolved towards CAM idling. It is, however, plausible that this adjustment was not an effect of the low night temperature per se but a consequence of cool-root induced drought stress. Apart from that, at the start of the photoperiod, membrane stability showed a depression which was directly counteracted by an increased generation of glucose, fructose and sucrose. From these observations, it can be concluded that the observed plasticity in CAM operation and metabolic flexibility may be recognized as important steps in the low night temperature acclimation of Phalaenopsis.

Increased grain yield and biomass allocation in rice under cool night temperature

The effects of different night temperatures on grain yield were examined in rice (Oryza sativa L. Akita-63) during the ripening period. Plants were grown under two different night temperatures (22 and 27°C) from anthesis to harvesting. The day temperature was maintained at 27°C in both treatments. Although the final biomass at harvest did not differ between the treatments, the dry weight of the panicles was significantly greater in the cool night temperature treatment. This increase in panicle weight was associated with increases in the 1000-kernel weight and the ratio of filled spikelets. Although panicle respiration in the high night temperature treatment decreased to almost zero just after the cessation of grain filling, the net CO2 fixation rate per day in the whole plant in this treatment tended to be higher, and this was associated with a higher level of starch accumulation. After grain filling, the starch content decreased and the final dry weight of other plant parts, including dead organs and new tillers, was greater in the high night temperature treatment. Thus, the noted decline in yield at the high night temperature led to changes in carbon allocation to new sinks for vegetative reproduction at the whole plant level. From these results, we considered the possibility that a cool night temperature tends to favor carbon allocation to panicles, resulting in higher yield.

Cool-night temperature induces spike emergence and affects photosynthetic efficiency and metabolizable carbohydrate and organic acid pools in Phalaenopsis aphrodite

After being acclimated to constant warm (28 degrees C day/28 degrees C night) and cool-night temperature (28 degrees C day/20 degrees C night) regimes in growth chambers for 2 weeks, the two groups of mature Phalaenopsis aphrodite subsp. formosana plants both clearly exhibited a diurnal oscillation of stomatal conductance, net CO(2) uptake rate, malate and starch levels, and the phosphoenolpyruvate carboxylase (EC 4.1.1.31) and NAD(+)-malic enzyme (EC 1.1.1.39) activities. Hence, P. aphrodite is an obligate crassulacean acid metabolism plant. Nevertheless, different night temperature greatly affected both the stomatal conductance and the contribution of ambient and respiratory CO(2) to the nocturnal accumulation of malate. However, the amounts of nocturnal accumulated malate and daily deposited starch appeared to have no significant difference between the two groups. These results demonstrate that P. ahrodite is congruent with the characteristics of CAM plants having great flexibility and plasticity in response to changes in environmental conditions. In addition, the formation of reproductive stem, viz. spike, was noticeably inhibited by a constant warm temperature, but induced by a fluctuating warm day and cool night condition. The relationship between the metabolic pool variation and spike induction of Phalaenopsis is also discussed.

Regulatory Mechanism of Anthocyanin Biosynthesis in 'Kyoho' Grape Berries Grown under Different Temperature Conditions

To clarify the mechanism regulating anthocyanin biosynthesis in ‘Kyoho’ grape berries grown under high temperature, we examined flavonoids accumulation and the activities of related enzymes as well as photoassimilates translocation on the berries. Anthocyanin content in the skin of berries of grape was lowered at 30 days after veraison when grown under high temperature condition (at consistently 30°C) as compared with berries at consistently 25°C or 30°C in the day and 15°C in the night concomitantly. Phenylalanine concentration in the skin and the photoassimilates partitioning to berry were also lower in those grown at 30°C than vines at 25°C or 30/15°C. While, phenylalanine ammonia lyase (PAL) activity in berries grown at 25°C was higher than that in berries grown at 30°C or 30/15°C. Berries grown at 30/15°C had the highest UDP-glucose : flavonoid 3-O-glucosyltransferase (UFGT) activity among three temperature conditions 30 days after veraison. These results suggest that grape berries grown at successive high temperature decrease anthocyanin accumulation in the skin by virtue of the decrease of the UFGT activities and the concentration of phenylalanine and photoassimilates partitioning to berry. On one hand, the grape berry grown under cool night temperature condition would result in high level of anthocyanin accumulation due possibly to great induction of UFGT activity and high phenylalanine accumulation.

Induction of rubber transferase activity in guayule ( Parthenium argentatum Gray) by low temperatures

The enzymatic activity of rubber transferase was determined in rubber particles purified throughout the year from three different lines of mature (5-years-old) guayule plants grown in the field in Phoenix, Arizona (33.40°N by 112.00°W, elevation 335 m), as well as in plants grown in controlled environment. Rubber transferase activity was environmentally-induced by cool night temperatures of ca. 20 °C, colder temperatures seeming not to be required. This is in contrast to reports that young guayule plants require temperatures of 7–10 °C for induction. Also, the cold temperature stimulus that induces rubber biosynthesis either is not perceived or translated by guayule seedlings until they are at least 200-days-old. However, branches less than 200-days-old on mature plants are stimulated by cool (20 °C) night temperatures to produce rubber.

Do muskmelons (Cucumis melo L.) set parthenocarpic fruits spontaneously?

SummaryGreenhouse experiments were conducted in the Newe Ya’ar Research Center, Israel, during the autumn and winter of 1999-2000, to examine whether muskmelons (Cucumis melo L.) are capable of setting parthenocarpic fruits without external induction. The cultivars CNY and CKR differed markedly in their ability to produce pistillate ¯owers under the experimental conditions. Nevertheless, both cultivars did set parthenocarpic fruits spontaneously, after emasculation and covering of the female ¯owers. In the autumn (late November), parthenocarpic fruit-set was promoted by cool night temperatures. However, the unfavourable winter climate (late January) limited fruit set in both parthenocarpic and pollinated treatments. There were no significant differences in fruit number per plant or in mean fruit weight between plants subjected to active hand pollination and those that underwent passive (covering pistillate ¯ower without emasculation) self-pollination, but the plants in each of these treatments produced more fruits than those in the parthenocarpy treatment. As expected, parthenocarpic fruits had no viable seeds. Fruits developed by passive pollination had significantly fewer seeds than those developed by active pollination treatments, but their seeds were larger and exhibited inferior germination. Pollen source (self or cross) had no significant effects on fruit set or on fruit weight, but it significantly affected the number of fully developed seeds in CKR in the autumn experiment. Comparison between the data on numbers and weights of seeds and fruits in the passive and in the active pollination treatments suggest that there is no cause-effect relationship between seed and fruit development in muskmelons.

Effect of plant growth temperature on antioxidant capacity in strawberry.

The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, and 30/22 degrees C) on phenolic acid, flavonol, and anthocyanin content and their antioxidant activities against peroxyl radicals (ROO(*)), superoxide radicals (O(2)(*)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radicals (OH(*)), and singlet oxygen ((1)O(2)) in fruit juice of Earliglow and Kent strawberry (Fragaria x ananassa Duch.) cultivars was studied. Pelargonidin-based anthocyanins such as pelargonidin 3-glucoside (291.3-945.1 microg/g fresh wt.), pelargonidin 3-rutinoside (24.7-50.9 microg/g fresh wt.), and pelargonidin 3-glucoside-succinate (62.2-244.0 microg/g fresh wt.) were the predominant anthocyanins in strawberry fruit juice. The content of cyanidin-based anthocyanins, cyanidin 3-glucoside and cyanidin 3-glucoside-succinate, was much lower than that of pelargonidin-based anthocyanins. Strawberry growth in high temperature conditions significantly enhanced the content of p-coumaroylglucose, dihydroflavonol, quercetin 3-glucoside, quercetin 3-glucuronide, kaempferol 3-glucoside, kaempferol 3-glucuronide, cyanidin 3-glucoside, pelargonidin 3-glucoside, pelargonidin 3-rutinoside, cyanidin 3-glucoside-succinate, and pelargonidin 3-glucoside-succinate in strawberry juice. Plants grown in the cool day and cool night temperature (18/12 degrees C) generally had the lowest phenolic acid, flavonols, and anthocyanins. An increase in night temperature from 12 to 22 degrees C, with the day temperature kept constant at 25 degrees C, resulted in a significant increase in phenolic acid, flavonols, and anthocyanins. These conditions also resulted in a significant increase in antioxidant capacity. The highest day/night temperature (30/22 degrees C) yielded fruit with the most phenolic content as well as ROO(*), O(2)(*)(-), H(2)O(2), OH(*), and (1)O(2) radical absorbance capacity. Fruit of Kent cv. strawberry had higher values of phenolic acid, flavonols, anthocyanins, and antioxidant capacities than fruit of Earliglow cv. strawberry under all temperature regimes.