Effect Of Low Night Temperature Research Articles

Low‐temperature nights delay the timing of breeding in a wild songbird

Global climate change has posed widespread challenges to the ecological process critical to the fitness of many wild organisms, such as reproductive phenology. Many bird species have advanced their reproductive phenology in response to the increases in spring temperatures. However, the mechanism of how climate influences the timing of breeding is still often unclear in many species. We explored the relationship between the timing of breeding and spring temperatures based on 14 years of data on hair‐crested drongos Dicrurus hottentottus in the wild. By applying a ‘sliding window' approach, we aimed to identify the time window and weather variable that best explains the timing of breeding at both population and individual levels. We found that the more nights with a minimum temperature below 17°C, around three weeks earlier than the peak reproduction, delayed the breeding time. Low night temperatures may force females to allocate more energy to thermoregulation and therefore physiologically constrain egg‐laying. Although annual minimum and maximum temperatures have increased over the study period, the timing of breeding showed no trend as there was no change in the number of low‐temperature nights in the relevant period across years. The repeatability of the laying date for individual females (R = 0.211) and across the years (R = 0.270) were low indicating that drongos were flexible in adjusting their breeding phenology to environmental variation. These results suggest an effect of low night temperature on avian breeding phenology. This effect may apply commonly across bird species considering shared physiological constraints.

Microclimate suitability for green and coloured sweet pepper hybrids in open and protected structures in sub-tropical humid climate of West Bengal

A study was undertaken for two consecutive seasons (autumn-winter) to evaluate the performance of three green, red and yellow-fruited sweet pepper hybrids in open field and under two protected structures (50% green shade net house and naturally-ventilated polyhouse) to understand the microclimate suitability for maximizing the productivity of these hybrids under sub-tropical humid climatic condition of eastern India. In this climatic condition, naturally-ventilated polyhouse was most suitable for enhancing fruit yieldof both green and coloured fruited hybrids. Open field condition was not suitable for both yellow and redfruited hybrids. Though green-fruited hybrids could be grown in open field condition, fruit yield was more than double under polyhouse. Shade net house could not be considered as a suitable protected structure for sweet pepper in this climatic condition because of reduced light intensity and high relative humidity inside it causing low fruit set and high incidence of bacterial wilt disease. Maximum/minimum temperature30oC to 33oC / 14oC to 17oC with comparatively reduced light intensity of 35,000 to 55,000 lux, prevention of adverse effect of low night temperature during winter and  60 per cent relative humidity condition during flowering, fruit set and fruit development period inside the naturally ventilated polyhouse were most suitable growing conditions for getting maximum productivity of both green and colour-fruited hybrids of sweet pepper.

Diurnal Temperature Variations Significantly Affect Cucumber Fruit Growth

Decreasing the temperature in heated greenhouses significantly reduces heat costs and CO2 emissions. However, the thermophile cucumber is known to be very sensitive to low temperatures. In particular, fruit growth decreases considerably as temperature declines. Nevertheless, reports show that cucumber can be grown successfully at low night temperatures. To explain this phenomenon, it is necessary to investigate the effect of the diurnal temperature variation on fruit growth. Fruit-bearing cucumber plants were grown in two experiments, either at a constant low temperature during the light and dark phase of 15 or 16 °C or at an extremely low temperature during the dark phase of 10 or 11 °C with an increase to 24 or 25 °C during the middle of the light phase resulting in a daily average of 15 or 16 °C, respectively. Introducing the diurnal temperature variation considerably increased fruit growth compared with cultivation at a constant temperature. The vegetative dry matter, however, was greater at a constant than at variable temperatures. Therefore, the total dry matter appeared to be unaffected by the treatments, meaning that photosynthesis was unaffected. Model calculations indicate that the relationship between temperature and fruit growth is not linear in the low-temperature range. For practical applications, it can be concluded that short daily periods with high temperature can mitigate the negative effect of low night temperature on fruit growth and yield.

Plant Physiological, Morphological and Yield-Related Responses to Night Temperature Changes across Different Species and Plant Functional Types.

Land surface temperature over the past decades has shown a faster warming trend during the night than during the day. Extremely low night temperatures have occurred frequently due to the influence of land-sea thermal difference, topography and climate change. This asymmetric night temperature change is expected to affect plant ecophysiology and growth, as the plant carbon consumption processes could be affected more than the assimilation processes because photosynthesis in most plants occurs during the daytime whereas plant respiration occurs throughout the day. The effects of high night temperature (HNT) and low night temperature (LNT) on plant ecophysiological and growing processes and how the effects vary among different plant functional types (PFTs) have not been analyzed extensively. In this meta-analysis, we examined the effect of HNT and LNT on plant physiology and growth across different PFTs and experimental settings. Plant species were grouped according to their photosynthetic pathways (C3, C4, and CAM), growth forms (herbaceous, woody), and economic purposes (crop, non-crop). We found that HNT and LNT both had a negative effect on plant yield, but the effect of HNT on plant yield was primarily related to a reduction in biomass allocation to reproduction organs and the effect of LNT on plant yield was more related to a negative effect on total biomass. Leaf growth was stimulated at HNT and suppressed at LNT. HNT accelerated plants ecophysiological processes, including photosynthesis and dark respiration, while LNT slowed these processes. Overall, the results showed that the effects of night temperature on plant physiology and growth varied between HNT and LNT, among the response variables and PFTs, and depended on the magnitude of temperature change and experimental design. These findings suggest complexities and challenges in seeking general patterns of terrestrial plant growth in HNT and LNT. The PFT specific responses of plants are critical for obtaining credible predictions of the changes in crop production, plant community structure, vegetation dynamics, biodiversity, and ecosystem functioning of terrestrial biomes when asymmetric night temperature change continues.

Effect of low night temperature on graft union formation in watermelon grafted onto bottle gourd rootstock

To explore the effects of low night temperatures on graft union formation in watermelon grafted onto bottle gourd rootstock, an anatomical study during the healing stage was performed. In the present study, we compared the morphological anatomy structures during the healing process in grafted watermelon seedlings under different night temperature treatments. The results showed that concrescence occurs fastest at the night temperature of 18°C, at which vascular bridges were connected to vascular bundles at 5days post-grafting (dpg). For night temperatures of 15°C and 12°C, vascular bridges were connected to vascular bundles at 7 dpg and 10 dpg, respectively. In general, healing rate slowed as night temperature decreased. Low temperatures delayed the differentiation of vascular tissue, which was not conducive to the connection of vascular bundles. The wider gully between the rootstock and scion cut surface caused the callus formation on both sides to fail to link, which turns to the formation of graft union unsuccessful. These results suggest that night temperatures are implicated in graft development in watermelon plants. A minimum temperature of 18°C is indicated during the graft union formation stage.

CARBOHYDRATE CONTENTS AND SOME GROWTH OF CURCUMA ALISMATIFOLIA IN RESPONSE TO LOW NIGHT TEMPERATURE TREATMENT

Decreasing of the night temperature in greenhouse during off-season production is a factor lead to the reduction of growth and flower quality in Curcuma alismatifolia. The effect of low night temperature on carbohydrate contents and some growth parameters in this plant was thus determined. Plants were grown under 30/24 o C (day/night temperature: DN/TN) as high night temperature (HNT) or under 30/18 o C as low night temperature (LNT) with 13 h daylength. The humidity and light levels were maintained at 70-80% RH and 270 μmol m -2 s -1 , respectively. Plant samples were harvested at flowering stage (12 weeks after planting). The results showed that glucose and fructose accumulation in leaf and storage roots were significantly decreased under LNT. Nevertheless, carbohydrate contents in rhizomes did not affected by LNT. The HNT treatment led to better plant growth in terms of total leaves area, leaves dry matter, rhizomes dry matter and number of shoots per clump. LNT increased rhizomes dry matter.

Low night temperatures inhibit galactinol synthase gene expression and phloem loading in melon leaves during fruit development

Low night temperatures seriously affect plant growth and fruit quality. To investigate the effect of low night temperatures on the expression of galactinol synthase genes (GOLS) and phloem loading of raffi� nose family oligosaccharides, particular stachyose and raffinose (RFO represents stachyose and raffinose in this paper) and to gain a better understanding of the relationship between the phloem loading of RFO and fruit development, melon (Cucumis melo L.) plants at the fruit development stage were treated with temper� atures of 28/12°C or 28/9°C (day/night) with 28/15°C as the control. Both the CmGOLS1 and CmGOLS2 gene expression and the activity of galactinol synthase were clearly repressed after treatments with 9 and 12°C at night, and the effect of 9°C was more obvious. Furthermore, low night temperatures inhibited photosyn� thesis and caused the lower amounts of sucrose to supply the RFO synthesis. However, the total soluble sugar, RFO, and sucrose contents were increased in leaves subjected to low night temperatures. It is supposed that low night temperature blocked symplastic phloem loading, which led to the accumulation of RFO in the leaf cells. With increasing content of RFO in the leaves, the expression of GOLS genes was inhibited according to the principle of feedback, and therefore the decreased expression of GOLS limited RFO synthesis and was indirectly harmful to phloem loading, thereby affecting fruit development.

Low Night Temperatures Inhibit Galactinol Synthase Gene Expression and Phloem Loading in Melon Leaves During Fruit Development

Low night temperatures seriously affect plant growth and fruit quality. To investigate the effect of low night temperatures on the expression of galactinol synthase genes (GOLS) and phloem loading of raffi nose family oligosaccharides, particular stachyose and raffinose (RFO represents stachyose and raffinose in this paper) and to gain a better understanding of the relationship between the phloem loading of RFO and fruit development, melon (Cucumis melo L.) plants at the fruit development stage were treated with temper atures of 28/12°C or 28/9°C (day/night) with 28/15°C as the control. Both the CmGOLS1 and CmGOLS2 gene expression and the activity of galactinol synthase were clearly repressed after treatments with 9 and 12°C at night, and the effect of 9°C was more obvious. Furthermore, low night temperatures inhibited photosyn thesis and caused the lower amounts of sucrose to supply the RFO synthesis. However, the total soluble sugar, RFO, and sucrose contents were increased in leaves subjected to low night temperatures. It is supposed that low night temperature blocked symplastic phloem loading, which led to the accumulation of RFO in the leaf cells. With increasing content of RFO in the leaves, the expression of GOLS genes was inhibited according to the principle of feedback, and therefore the decreased expression of GOLS limited RFO synthesis and was indirectly harmful to phloem loading, thereby affecting fruit development.

Night Temperature and Source-sink Effects on Growth, Leaf Carbon Exchange Rate, and Carbohydrate Accumulation in Bell Pepper Ovaries

Low night temperatures and/or high source-sink ratios increase ovary swelling and subsequent fruit malformation in many sweet peppers (Capsicum annuum), including bell pepper. Although this response has been correlated with increased ovary carbohydrate accumulation, evidence for this is limited. Furthermore, it is unknown how the combined effects of night temperature and source-sink ratio affect ovary carbohydrate accumulation and ovary swelling. The objectives of the present work were to determine night temperature and source-sink effects on ovary swelling, net carbon exchange rate (CER), and soluble sugar and starch concentrations in bell pepper ovaries at anthesis. Source-sink and temperature effects were tested by comparing fruiting (low source-sink ratio or high sink demand) with non-fruiting (high source-sink ratio or low sink demand) ‘Legionnaire’ bell pepper plants grown at 22/20 °C [high night temperature (HNT)] or 22/12 °C [low night temperature (LNT)] day:night temperatures. Flowers that opened after imposition of the temperature and fruiting treatments were harvested at anthesis. Ovaries from harvested flowers were weighed and analyzed for non-structural carbohydrates. Leaf gas exchange measurements were performed every 3 days. Ovary fresh weight of flowers harvested at anthesis was highest in non-fruiting plants under LNT and lowest in plants grown under HNT regardless of fruiting status. Mean CER averaged over the experimental period was significantly higher in fruiting plants under HNT compared with all other treatments. There were no significant interactions between night temperature and fruiting status on ovary soluble sugar or starch concentrations. Low night temperature increased glucose, fructose, and starch concentration and decreased sucrose concentration in the ovary wall compared with HNT. There were no differences in soluble sugar or starch concentrations in the ovary wall between fruiting and non-fruiting plants. Thus, although both low temperature and high source-sink ratio (i.e., non-fruiting plants) resulted in ovary swelling, the mechanisms appear to differ. Whereas LNT effects on ovary swelling were associated with increased ovary carbohydrate accumulation, this association was not apparent when ovary swelling occurred in response to high source-sink ratios.

The Effect of Low Night and High Day Temperatures on Photosynthesis in Tomato

If low night temperatures can be combined with high day temperatures, providing optimal growth conditions for plants, a significant energy saving can be achieved in greenhouses. Lowering the night temperature from 18˚C to 10˚C - 11˚C for 8 h had no negative effect on the CO2 exchange rate (CER) during the following light period in tomato. This was found both in plants grown in artificial light only or in combination with daylight. Allowing the temperature to increase from 20˚C to about 40˚C, in parallel with an increasing solar photon flux density (PFD) from 0 up to about 800 µmol·m −2 ·s −1 in the greenhouse during summer, progressively increased CER when the CO2 concentration was maintained at 900 µmol·mol −1 . At 400 µmol·mol −1 CO2, maximum CER was reached at about 600 µmol·m −2 ·s −1 PFD combined with a temperature of 32˚C, and leveled out with a further increase in PFD and temperature. Maximum CER at high CO2 concentration was around 100% higher than at low CO2 level. Under early autumn conditions, CER increased up to about 500 µmol·m −2 ·s −1 PFD/32˚C at low CO2 and up to about 600 µmol·m −2 ·s −1 PFD/35˚C at high CO2. An elevated CO2 level doubled the CER in this experiment as well. Measurements of chlorophyll fluorescence showed no effect of low night temperature, high day temperature or CO2 concentration on the quantum yield of photosynthesis, indicating that no treatment negatively affected the efficiency of the photosynthetic apparatus. The results showed that low night temperatures may be combined with very high day temperatures without any loss of daily photosynthesis particularly in a CO2 enriched atmosphere. If this can be combined with normal plant development and no negative effects on the yield, significant energy savings can be achieved in greenhouses.

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.

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.

Low night temperature effects on photosynthetic performance on two grapevine genotypes

The functional activities of the photosynthetic apparatus of two grapevine genotypes (Vitis vinifera L. cvs. MĂźller-Thurgau and Lagrein) were investigated after low night temperature (LNT) treatment for 7 d. LNT caused important reductions of the net photosynthetic rate (PN) of Lagrein plants due to non-stomatal components. These non-stomatal effects were not evident in MĂźller-Thurgau. At LNT treatment, the contents of photosynthetic pigments decreased significantly in Lagrein, but in MĂźller-Thurgau the contents of chlorophyll (Chl) remained unchanged whereas the contents of carotenoids (Car) increased. An increase and decrease of Chl a/b was shown in MĂź ller-Thurgau and Lagrein stressed plants, respectively. RuBPC activity and content of soluble proteins were also significantly reduced in Lagrein. Under LNT treatment, photosystem (PS) 2 was markedly more inhibited in Lagrein than in MĂźller-Thurgau. The decrease in PS 2 activity in Lagrein was mostly due to the marked loss of D1, 47, 43, 33, 28-25, 23 and 17 kDa proteins determined by immunological and SDS-PAGE studies.

Photosynthesis and Rubber Production in Transgenic Guayule (Parthenium argentatum, Gray) in Response to Cold Night Temperatures

Rubber production in guayule (Parthenium argentatum, Gray) is highest in the winter months. It has been suggested that lower nighttime temperatures stimulate rubber production. Higher rubber production could be the result of up regulation of the enzymes involved in rubber synthesis, or acclimation of the photosynthetic apparatus to cold temperatures, making photosynthates available for rubber production when the plants are not actively growing, or a combination of the two factors. The effect of low night temperatures on photosynthesis and rubber production was examined in greenhouse grown plants. The experiment was set up as a split plot with different sub plots enclosed in heated or non-heated containers during the night. Those placed in non-heated containers were exposed to the ambient night temperatures of the greenhouse. During the growing season, growth was measured as change in height, and midday and diurnal photosynthetic measurements were collected. At harvest fresh and dry weight of both roots and shoots were taken. Resin and rubber were then extracted with acetone and cyclohexane respectively. Midday photosynthesis was as high or higher in cold night plants than in the warm night plants. In addition, the cold night treatment had lower growth than the warm night treatment. Percent resin and rubber were significantly higher in both shoots and roots of cold night plants, as was the overall yield of rubber. An increase in photosynthetic rate in the cold night treatment, without the concomitant increase in growth seen in the warm night treatment, could account for the increase in rubber production during the winter months.

The effect of low night temperatures on carbohydrates metabolism in developing pollen grains of pepper in relation to their number and functioning

Four pepper cultivars were grown under winter low night temperature (LNT) conditions (night temperature of 10±2 °C and day temperature which did not exceed 24 °C) in a greenhouse in Bet Dagan, Israel. In all four cultivars, LNT conditions caused a decrease in the number of pollen grains and a reduction in their germinability, in comparison with pollen of control plants grown in another greenhouse under higher temperature conditions (night temperature of 20±2 °C and similar day temperatures). Analysis of carbohydrates content in the later stages of pollen development revealed that LNT caused a reduction in starch concentration 4 days before anthesis (A-4), and in the concentrations of sucrose and reducing sugars (glucose and fructose) at anthesis (A). It is suggested that low temperatures hinder pollen functioning in pepper, by interfering with starch accumulation at A-4, thereby decreasing the concentrations of soluble sugars in the mature pollen grains. The fruits of the LNT-grown plants, except for cv. Devilla, were smaller, seedless and misshapen. The reason for the ability of cv. Devilla to set seeds and normal fruits under LNT conditions need further investigation.

Response of maize leaf photosynthesis to low temperature during the grain-filling period

The response of dry matter accumulation and leaf photosynthesis in maize ( Zea mays L.) to low temperature has been documented during early phases of development, but little is known about the low-temperature response of maize during later phases of development. Studies were conducted in 1999 at the Cambridge Research Station, Ontario, Canada, to quantify the effect of low night temperature during grain filling on leaf photosynthesis of short-season maize hybrids. Plants were grown in a hydroponic system in the field with plants in the low-night temperature treatments exposed to 4°C from late afternoon (17:00 h) to the next morning (9:00 h). Plants of three maize hybrids (i.e., an older hybrid, Pride 5, and two more recent hybrids, Pioneer 3902 and Cargill 1877) were exposed to one night or three consecutive nights of 4°C at weekly intervals from tasseling to 6 weeks after silking. Carbon exchange rate (CER) was measured at 10:00, 12:00, 14:00, and 16:00 h on the second leaf above that subtending the topmost ear. Dark-adapted chlorophyll fluorescence ( F v/ F m) was measured at 9:00 h at 6 weeks after silking. Leaf CER of control plants declined almost linearly from about 50 μmol m −2 s −1 at tasseling to about 20 μmol m −2 s −1 at 6 weeks after silking with the rate of decline in the older hybrid approximately two times greater than that in the two newer hybrids. No trend in the reduction in cold-stressed leaf CER relative to the field-grown control was apparent from tasseling to 6 weeks after silking. Reduction in CER was greater during the morning than during the afternoon after exposure to 4°C and the reduction in leaf CER increased from 19.4% after one night, to 25.8% after two nights, and 30.2% after three nights. Mean reduction in leaf CER after one night at 4°C differed significantly among the three hybrids and was 29.7% for Pride 5, 15.4% for Pioneer 3902, and 13.5% for Cargill 1877. The reduction in leaf CER due to low night temperature was associated with a reduction in leaf chlorophyll fluorescence. In conclusion, maize hybrids differ significantly in leaf CER response to cold night temperature during the grain-filling period.

Histological examination of low temperatures or TIBA-induced swelling of pepper ovaries

The ovaries of pepper (Capsicum annum L.) plants grown under low night temperatures (12 °C) were larger than those of plants grown under high night temperatures (18 °C). TIBA, applied to young flower buds grown under the higher temperature regime markedly stimulated ovary swelling, similarly to the effect of low night temperatures, whereas, NAA had a much smaller effect. STS or AOA did not reverse or attenuate the effect of either low temperatures or of TIBA. Histological examination of various tissues across the ovaries revealed marked increases in transverse and longitudinal diameters of cell of the swelled ovaries, concomitantly with a smaller increase in the number of cells in the receptacle and placenta. It is suggested that the swelling induced by low night temperatures or TIBA results mostly from the enlargement of all the ovary cells, and only to a smaller extent, by an increase in cell number in some of the ovary tissues. Since TIBA, an auxin transport inhibitor, causes auxin accumulation in the treated organ – in this case the developing ovary – and the auxin NAA stimulated ovary growth, one may conclude that auxins are involved in the observed ovary enlargement, whereas ethylene has no role in this phenomenon.

Response of Tropical and Temperate Soybean Genotypes to Temperature During Early Reproductive Growth1

Twelve soybean [Glycine max (L.) Merr.] lines of tropical and temperate origin were grown to anthesis and then subjected to a range of thermal regimes, using growth cabinets, to test their sensitivity to low temperature during early reproductive growth. Plants were grown under an 11‐h photoperiod with 30/20°C day/night, 12‐h thermoperiods prior to flowering, then during and after flowering, with all eight combinations of 20°C and 30°C day and 8, 12, 16, and 20°C night thermoperiods. There were large differential responses among lines in the sensitivity of podset to low night temperature. As a group, lines of tropical adaptation were more sensitive than temperate lines but there was variation among lines in both groups. The most sensitive (tropical) line, No. 29, failed to set pods in 8 and 12°C night temperatures while the least sensitive (temperate) line, Fiskeby V, set pods in all thermal regimes. Failure of lines to set pods in the lowest night temperatures was associated with pollen abnormalities. With the exception of Fiskeby V, there was little evidence that high day temperature compensated for the effect of low night temperature on podset. The greater sensitivity of the tropical lines to low temperature was consistent with field experience in northern Australia and it is suggested that breeding strategies for the dry (winter) season of the low latitude tropics, particularly for inland and for elevated areas, must seek to develop lines with less sensitivity to low temperature.

Night Temperature Effects on Morphology, Phenology, Yield and Yield Components of Indeterminate Field‐Grown Soybean1

AbstractSmall changes in geography and topography can result in great differences in night temperature. Indeterminate soybeans [Glycine max(L.) Merr. ‘S09‐90’] of Maturity Group 0 were grown under field conditions in 1981 and 1982 to assess the effect of low night temperature on growth and seed yield. The soil was a Woodburn silt loam (fine‐silty, mixed, mesic Aquultic Argixerolls). Mean minimum night temperature treatments were: Check (uncontrolled, ca. 10°C), 16±1°C and 24±2°C. Elevated night temperatures were achieved by enclosing the plots at night in polyethylene‐covered chambers and increasing chamber temperature with electric heaters. The chamber covers were removed each morning to provide natural field conditions during the daylight hours. Treatments were applied from 2 weeks after crop emergence until physiological maturity. Higher night temperatures enhanced vegetative growth. However, morphological characteristics, e.g., plant height, number of nodes, and number of auxiliary branches were not significantly (P < 0.05) different among the treatments at maturity since the growth of these components also terminated earlier for plants receiving higher night temperatures. Warmer night temperatures considerably shortened the time period between plant emergence and appearance of first flower (R1) and appearance of flowers at the node immediately below the uppermost node (R2), while they had little additional effect on the subsequent reproductive development. Physiological maturity (R7), however, was hastened by higher night temperatures. Accumulated growing degree‐days appeared to be of value for the prediction of all developmental stages and were a good indicator of the time period between emergence and physiological maturity of plants within treatments. Plants with warmer nights, however, accumulated more heat units than the check for the onset of all developmental stages. Seed weight/plant increased above the check by 27 and 37% for 16°C, and 20 and 23% for the 24°C treatments in 1981 and 1982, respectively. The growth of individual seeds appeared to be most responsive to night temperatures, and increased seed size (1000‐seed weight) accounted for the seed yield increase of both treatments. Final numbers of seeds/plant and pods/plant were not significantly affected by the treatments. The number of seeds/pod for the 24°C treatment was, however, significantly greater than the check. The data indicate that the genetic potential for seed yield of indeterminate soybeans is not realized under low night temperatures. This study emphasizes the importance of night temperatures as a potential criterion for developing new soybean cultivars.

POLLEN GERMINATION AND CHILLING SENSITIVITY IN TWO TOMATO CULTIVARS OF DIFFERING SENSITIVITY TO COOL NIGHT TEMPERATURE

The effect of low night temperature on pollen tube formation and chilling sensitivity was compared in two tomato cultivars, Ontario 7515, free-setting at low temperature, and Ohio MR13, poor-setting at low temperature. The rate and extent of pollen grain germination in the Ontario 7515 cultivar far exceeded that of pollen grains obtained from the Ohio MR13 cultivar. In addition, the rate of pollen tube growth was greater in the free-setting cultivar than the poor-setting cultivar. No major differences were observed in the chilling sensitivity of the vegetative parts of these two tomato cultivars. It is concluded that the differential ability of these two tomato varieties to set fruit during growth at cool, night temperatures may be a function of differential flower production and a differential rate of pollen grain germination rather than a differential chilling sensitivity of the vegetative plant.