Effect of sub-optimal root zone temperatures at varied nutrient supply and shoot meristem temperature on growth and nutrient concentrations in maize seedlings (Zea mays L.)

Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth.     

The effect of root temperature on growth of curled parsley

Summary Curled parsley was grown at root-zone temperature (RZT) of 18, 21, 24, 27 and 36°C at air temperature (AT) of 18 and 21°C. Maximum growth was obtained at 18°C AT and 24°C RZT, but there were no significant differences between 18 and 27°C RZT. Shoot and root growth were severely inhibited at 36°C constant RZT. The growth was also retarded when RZT rose to 36°C for 30 minutes per day, even when compared to a RZT of constant 27°C. This indicates that a short exposure to RZT above 30°C retards growth. A relatively low daily average RZT did not compensate for the damage caused by a short daily high temperature exposure. Optimum temperature for curled parsley seems to be about 21°C. Report No. 316.     

Differences between maize and wheat in growth-related nutrient demand and uptake of potassium and phosphorus at suboptimal root zone temperatures

The effects of low root zone temperatures (RZT) on nutrient demand for growth and the capacity for nutrient acquisition were compared in maize and wheat growing in nutrient solution. To differentiate between direct temperature effects on nutrient uptake and indirect effects via an altered ratio of shoot to root growth, the plants were grown with their shoot base including apical shoot meristem either within the root zone (low SB), i.e. at RZT (12°, 16°, or 20°C) or, above the root zone (high SB), i.e. at uniformly high air temperature (20°/16° day/night).At low SB, suboptimal RZT reduced shoot growth more than root growth in wheat, whereas the opposite was true in maize. However, in both species the shoot growth rate per unit weight of roots, which was taken as parameter for the shoot demand for mineral nutrients per unit of roots, decreased at low RZT. Accordingly, the concentrations of potassium (K) and phosphorus (P) remained constant or even increased at low RZT despite reduced uptake rates.At high SB, shoot growth at low RZT in both species was higher than at low SB, whereas root growth was not increased. At high SB, the shoot demand per unit of roots was similar for all RZT in wheat, but increased with decreasing RZT in maize. Uptake rates of K at high SB and low RZT adapted to shoot demand within four days, and were even higher in maize than in wheat. Uptake rates of P adapted more slowly to shoot demand in both species, resulting in reduced concentrations of P in the shoot, particularly in maize.In conclusion, the two species did not markedly differ in their physiological capacity for uptake of K and P at low RZT. However, maize had a lower ability than wheat to adapt morphologically to suboptimal RZT by increasing biomass allocation towards the roots. This may cause a greater susceptibility of maize to nutrient deficiency, particularly if the temperatures around the shoot base are high and uptake is limited by nutrient transport processes in the soil towards the roots.     

Influence of Thermoperiod on Growth and Development in Cucumber

We studied the influence of gradient temperature regimes on various parameters of the formation of shoots and roots of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth shoots organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 W/m², and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25°C for all growth indices of shoots and 20°C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. Outside the optimum area, the effects of gradient temperatures differed. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15°C) and optimal temperatures (25°C), which was earlier described for animals. The 15/35 and 35/15°C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of gradient temperatures on the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the responses to temperature gradients are similar in different groups of ectotherms.     

Temperature behavioral responses of the American eel,Anguilla rostrata (Lesueur), from Maryland

Acute temperature preference tests were conducted with American eels, Anguilla rostrata, collected from Maryland's eastern shore. Eels were acclimated to temperatures of 6, 12, 18, 24 and 30°C. Final temperature preferendum was 16.7°C. Data differ from the temperature responses of the majority of fishes tested to date in that acclimation temperature did not influence selected temperatures. Similar results were obtained for various other fishes (Oncorhynchus, Salmo, Salvelinus) by other investigators. Behavioral responses at various acclimation temperatures were observed.     

Pollen selection for low temperature adaptation in tomato

Summary Pollen selection experiments were conducted in tomato to determine the effects of low temperature conditions during pollination on the rate of root elongation of the progeny. Pollen was harvested from an F₁ interspecific hybrid between a high altitude Lycopersicon hirsutum accession and the cultivated tomato L. esculentum. The pollen was applied to stigmas of malesterile L. esculentum plants maintained in growth chambers set at either 12°C/7°C or 24°C/18°C. BC₁ seeds from the low and normal temperature crosses were germinated and root elongation rate was measured at either 9°C or 24°C. At 9°C, the rate of root elongation for progeny of the low temperature crosses was higher than for progeny of crosses at normal temperatures; at 24°C the rate of root elongation was similar for the two crossing treatments. To compare the temperature responses of the two backcross populations we also calculated the relative inhibitory effect of low temperature on the rate of root elongation: the ratio between the rate of root elongation at 9°C to that at 24°C. Root elongation of seedlings from the low temperature crosses was less inhibited by the cold than root elongation for progeny of the normal temperature crosses. These results suggest a relationship between pollen selection at low temperatures and the expression of a sporophytic trait under the same environmental stress.     

Life history ofAphis gossypii on cucumber: influence of temperature, host plant and parasitism

Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2 days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9 and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25°C (r _m =0.556 day⁻¹). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀ on leaves of the lower, middle and upper leaf layer, respectively). Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to the longevity of aphids not stung byA. colemani.     

Preincubation of Bradyrhizobium japonicum with Genistein Accelerates Nodule Development of Soybean at Suboptimal Root Zone Temperatures

In the soybean (Glycine max [L.] Merr.) N2-fixing symbiosis, suboptimal root zone temperatures (RZTs) slow nodule development, especially at temperatures below 17[deg]C. A step in the infection process that occurs within the first 24 h is particularly sensitive to suboptimal RZT. The first phase in the establishment of the soybean-Bradyrhizobium japonicum symbiosis is the exchange of recognition molecules. The most effective plant-to-bacterium signal is genistein. Binding of genistein to B. japonicum activates many of the B. japonicum nod genes. To our knowledge, the potential of sub-optimal RZT to disrupt this interorganismal signaling has not previously been investigated. Controlled environment experiments were conducted to determine whether the preincubation of B. japonicum with genistein increases soybean nodulation and N2 fixation at suboptimal RZT and whether the time between inoculation and root-hair curling is shortened by genistein application. The results of these experiments indicated that (a) genistein application increased soybean nodulation at suboptimal RZTs (17.5 and 15[deg]C) but not at the optimal RZT (25[deg]C); (b) the period between inoculation and root-hair curling was shortened by inoculation with bradyrhizobia preincubated with genistein; (c) at 17.5 and 15[deg]C RZT, the onset of N2 fixation occurred earlier in plants that received genistein-treated bradyrhizobia than in plants inoculated with untreated bradyrhizobia; (d) over the tested concentration range, genistein application at 15 to 20 [mu]M was the most effective in stimulating nodulation; and (e) between 25 and 15[deg]C, as RZT decreased, there was an increase in the nodulation-stimulating potential of genistein.     

The effects of low root-zone temperature stress on two soybean (Glycine max) genotypes when combined with Bradyrhizobium strains of varying geographic origin

In areas with short growing seasons, poor early vegetative growth of soybean (Glycine max [L.] Merr.) is often attributed to the restrictive effect of cool soil conditions on nodulation and N₂-fixation by this subtropical grain legume. However, there are few studies regarding potential genetic variability of soybean and Bradyrhizobium japonicum genotypes for nodulation at cool root-zone temperatures (RZT). Experiments were conducted to (1) test for a threshold temperature for low RZT inhibition of soybean nodulation and (2) ascertain whether this threshold temperature response depends mainly on the micro- or macrosymbiont. In experiment 1 soybean seedlings (Glycine max [L.] Merr. cv. Maple Arrow) were inoculated with 1 ml of a log phase culture of B. japonicum strain 532C, H8 or H15 (the latter two strains were isolated from cold soils of Hokkaido, northern Japan) and maintained at either 16, 17.5, 19 or 25°C RZT. In experiment 2 seedlings of cv. Maple Arrow and a cold-tolerant Evans isoline were combined with strain 532C and two Hokkaido strains (H5, H30) at both 19 and 25°C RZT. Results indicated that N₂-fixation at 44 days after inoculation was substantially reduced (30–40%) by RZT as high as 19°C, due to development of less nodule mass and to a delay in the onset of N₂-fixation and a small decrease in the number of nodules formed. However, the number of nodules formed was sharply reduced and the time required for the first appearance of nodules was significantly delayed below an RZT of 17.5°C. Differences between cultivars for nodulation and N accumulation were apparent at 25°C, but were abolished by growth at 19°C, indicating that, in spite of differences in growth potential between the cultivars under optimum RZT, both cultivars were equally limited by low RZT. Differences between B. japonicum strains were consistent across temperatures and were largely attributable to higher rates of specific nodule activity recorded for strain 532C, which seemed well adapted to low RZT. These results suggest that the host plant mediates the sensitivity of N₂-fixation under low RZT and that inoculation with B. japonicum strains from cold environments is unlikely to enhance soybean N₂-fixation under cool soil conditions.     

Effect of soil temperature on nutrient allocation and mycorrhizas in Scots pine seedlings

We studied the effect of soil temperature on nutrient allocation and mycorrhizal development in seedlings of Scots pine (Pinus sylvestris L.) during the first 9 weeks of the growing season. One-year-old seedlings were grown in Carex-peat from a drained and forested peatland at soil temperatures of 5, 9, 13 and 17 °C under controlled environmental conditions. Fourteen seedlings from each temperature treatment were harvested at intervals of three weeks and the current and previous year's parts of the roots, stems and needles were separated. Mineral nutrient and Al contents in all plant parts were determined and the tips and mycorrhizas of the new roots were counted. Microbial biomass C and N in the growth medium were determined at the end of the experiment. None of the elements studied, except Fe, were taken up from the soil by the seedlings during the first three weeks. Thereafter, the contents of all the elements increased at all soil temperatures except 5 °C. Element concentrations in needles, stems and roots increased with soil temperature. Higher soil temperature greatly increased the number of root tips and mycorrhizas, and the numbers of mycorrhizas increased more than did the length of new roots. Cenococcum geophilum was relatively more abundant at lower soil temperatures (5 and 9 °C) than at higher ones (13 and 17 °C). A trend was observed for decreased microbial biomass C and N in the peat soil at higher soil temperatures at the end of the experiment.     

Effect of Root Zone Temperature and Shoot Demand on Uptake and Xylem Transport of Macronutrients in Maize (Zea mays L.)

The effect of shoot demand for nutrients on nutrient uptakeand translocation in the xylem exudate was studied in maizegrowing in nutrient solution at uniform shoot zone (24/2C,day/night), but different root zone temperatures (RZT: 12C,18C, 24C). The shoot base (apical shoot meristem and zoneof leaf extension) was either kept within or lifted above thecooling zone. In plants with their shoot base above the coolingzone (RZT: 12C and 18C) shoot growth was significantly increasedbut not root growth. Therefore, at suboptimal RZT shoot freshweight increment d^–1 g^–1 root fresh weight, whichwas taken as a parameter for the shoot demand for nutrientsper unit root, varied strongly depending on the temperatureof the shoot base (shoot base temperature, SBT). In short-term studies (2 h and 1 d after onset of temperaturetreatment) rates of nutrient (nitrogen, N; potassium, K; phosphorus,P; calcium, Ca) uptake or translocation in the xylem exudatewere markedly decreased at suboptimal RZT (12C, 18C), irrespectiveof the SBT. In long-term studies (3, 5, and 10 d after onsetof temperature treatment) uptake and translocation of K, N,and Ca, but not P, increased in plants at suboptimal RZT whenthe shoot demand was high (shoot base above the cooling zone)but decreased when the shoot demand was low (shoot base withinthe cooling zone). These results suggest, that the increase of translocation ratesof N, K, and Ca after long-term exposure to suboptimal RZT wasa consequence of a higher shoot demand per unit root fresh weightand not due to a direct temperature effect on the nutrient uptakesystem. Key words: Xylem exudate, nutrient translocation, root zone temperature, shoot demand, nutrient circulation     

Factors affecting low temperature preservation of the marine rotifer Brachionus rotundiformis Tschugunoff

Experiments were performed to determine suitable conditions for low temperature preservation of small S (Fukuoka) and ultra-small SS (Thai) strains of B. rotundiformis. For this, single rotifers (an adult bearing one egg or a 4-h neonate) were incubated for 10 days in 1 ml seawater (22 ppt salinity). The highest survival was achieved at 10 and 12 °C for S-strain and 12 °C for SS-strain. The effect of salinity, change of culture medium and feeding regime were further tested on rotifers (300 ind. ml^–1) cultured in vials containing 10 ml seawater and microalgae at 12 °C. Survival of S-strain was highest (55.5±0.8%) at 35 ppt, while SS-strain survived best (43.1±2.6%) at 17 ppt. Survival was suppressed by changing the culture medium every 4 days. Feeding rotifers every 2 days yielded better survival (66.2±6.6%: S-strains, cultured at 35 ppt and 81.8±5.2%, SS-strains cultured at 17 ppt) than feeding them only at the beginning of the experiment or at 4-day intervals. An acclimation at 20 °C for 24 h before transferring them from their usual culture temperature (28 °C) to 12 °C resulted in higher survival of SS-strain. For S-strain, however, no significant improvement resulted from acclimation. SS-strain was more susceptible to lower temperature and higher salinity than S-strain.     

Field and laboratory studies on the timing of oviposition and hatching of the western black-legged tick, Ixodes pacificus (Acari: Ixodidae)

The timing of oviposition and hatching of Ixodes pacificus was investigated in the field and at constant temperatures in the laboratory. Replete females held at temperatures between 9 and 29°C began depositing eggs a mean of 9–70 days after drop off. Egg masses held between 12 and 25°C commenced hatching 25–178 days after the onset of oviposition. Eggs held at 9 or 29°C did not hatch. The lower temperature thresholds for development (LTD) for oviposition and hatching were 6.5 and 9°C, respectively. The number of degree days required for oviposition and hatching was 173 and 588, respectively. Replete females placed in the field on 2 December through to 8 March deposited eggs from 2 February through to 24 April; the eggs commenced hatching between 2 July and 21 August. Unfed larvae from two of 20 egg masses survived through the winter and fed readily when exposed to deer mice (Peromyscus maniculatus) on 22 April. Replete larvae were returned to the field and moulted between 9 and 21 August. Larvae exposed to deer mice in August, 4 weeks after hatching, also fed readily. Although further studies are needed to clarify the timing of nymphal development, the present study suggests that I. pacificus requires more than 1 year to complete its life cycle.     

Effect of rearing temperature and larval density on larval survival, age at pupation and adult size of Anopheles gambiae

The effects of temperature and larval density on survival of larvae, growth rate, age at pupation, and adult size (measured as wing length and dry weight) of laboratory-reared Anopheles gambiae (Diptera: Culicidae) were studied. Larvae were reared at three temperatures (24, 27 and 30°C) and three densities (0.5, 1 and 2 larvae/cm²). The effects of density and temperature strongly interacted to determine the mosquitoes' life-history parameters. Survival was highest at the intermediate temperature of 27°C. The differences between the temperatures increased with increasing density. At 30°C survival decreased as density increased, but at 27°C increasing density led to higher survival. Age at pupation increased as temperature decreased from 30°C to 24°C and as density decreased from 2 to 0.5 larvae/cm². Adult size also increased as temperature decreased, but showed a negative correlation with density only at 27°C. In contrast, at 24°C and 30°C a decrease in density led to a decrease in adult size. Growth rate showed a similar pattern. At 27°C growth rate decreased as density increased, but at other temperatures the opposite trend was observed.     

Effects of root zone temperature and paraquat in the induction of oxidative stress in <Emphasis Type="Italic">Trichosanthes cucumerina</Emphasis> L.

We investigated the influence of root zone temperature (RZT) and the aerial application of paraquat on stress defence mechanisms of Trichosanthes cucumerina L. To achieve this objective, T. cucumerina cv Green was grown with roots at 25 and 30°C root zone temperature and maintained at 20 ± 1°C air temperature in a growth chamber. These RZT and air temperature had earlier been shown to favor growth and fruit production in T. cucumerina. Plants at each RZT were subjected to paraquat treatment (+P) and without paraquat treatment (−P). Paraquat (0.2 mmol/L) was applied as aerial spray. Results showed that the individual main effects of RZT and paraquat treatments significantly affected the chlorophyll fluorescence and gas exchange parameters, while the interaction of both treatments had no significant effect. Results showed that the total phenolics and ascorbic acid contents of T. cucumerina at 30°C were significantly higher than at 25°C. The T. cucumerina plants in +P treatment recorded significantly lower maximum photochemical efficiency (F _v/F _m), net photosynthesis (A), transpiration rate (E), intercellular CO₂ concentration (C _i) and stomatal conductance (g ₁) compared to untreated plants. Also, plants raised at 30°C recorded significantly higher F _v/F _m, A, E, C _i and g ₁ compared to plants raised at 25°C. Plants that were sampled at 48 h after paraquat treatment recorded a higher degree of oxidative damage compared to those sampled at 24 h after treatment. We showed that the degree of damage suffered by T. cucumerina, when treated with paraquat either at 25 or 30°C RZT was similar at 48 h after treatment. We concluded that either at 25 or 30°C, exposure of T. cucumerina to paraquat would impose the same degree of oxidative damage.     

Life history study of Thrips setosus

Development, reproduction and population growth of Thrips setosus Moulton (Thysanoptera, Thripidae), reared on a leaf of kidney bean, was studied under six different constant temperatures, and the effect on reproduction of short photoperiod during immature stages was examined. Survival rates from hatch to adult were more than 67.5% at temperatures between 17.5 and 27.5 °C, but less than 55% at 30 °C. Developmental rates increased linearly as rearing temperature increased. A total of 181.1 degree-days, above a developmental zero of 12.5 °C, were required to complete development from egg to adult oviposition. These data were related to records of field temperatures in Kurashiki in western Japan, and an estimate produced that, under outdoor conditions, a maximum of between seven and 12 generations could have developed annually between 1990 and 1999. There were no significant differences in mean adult longevity and mean fecundity among three temperatures (20, 22.5 and 25 °C). The intrinsic rate of natural increase (r _m) was 0.1997 at 25 °C. Reproductive diapause was induced by a photoperiod less than 12 h at 20 °C.     

Effect of constant temperatures on germination, radial growth and virulence of Metarhizium anisopliae to three species of African tephritid fruit flies

The effect of temperatureon conidial germination, mycelial growth, andsusceptibility of adults of three tephritidfruit flies, Ceratitis capitata(Wiedemann), C. fasciventris (Bezzi) andC. cosyra (Walker) to six isolatesof Metarhizium anisopliae were studied inthe laboratory. There were significantdifferences among the isolates in the effect oftemperature on both germination and growth.Over 80% of conidia germinated at 20, 25 and30°C, while between 26 and 67% conidiagerminated at 35°C and less than 10% at15°C within 24 hours. Radial growth was slowat 15°C and 35°C with all of theisolates. The optimum temperature forgermination and mycelial growth was 25°C. Mortality caused by the six fungal isolatesagainst the three fruit fly species varied withtemperature, isolate, and fruit fly species.Fungal isolates were more effective at 25, 30and 35°C than at 20°C. The LT₉₀values decreased with increasing temperature upto the optimum temperature of 30°C. Therewere significant differences in susceptibilitybetween fly species to fungal infection at allthe temperatures tested.     

Diapause induction in the codling moth, Cydia pomonella: effect of prediapause temperatures

The effect of four prediapause temperatures (18, 22, 26 and 30°C) on the photoperiodic response of the codling moth, Cydia pomonella (L.), was studied under controlled conditions. The highest rates of diapause were recorded, for all day-lengths, at temperatures of 22 and 26°C while relatively lower rates of diapause were elicited at 18 and 30°C. The same trend was demonstrated by projecting the values of the critical photoperiod which induces 50% diapause (=CPhP₅₀) over the prediapause temperature. The change in diapause incidence as a function of photoperiod, at all prediapause temperatures, exhibited a response characteristic of long-day insects, i.e. high rates of diapause at short days (12–13.5 h) and a decrease in diapause incidence at long days (14–15 h). The results for temperatures 22, 26 and 30°C support the view that lower prediapause temperatures enhance diapause induction, at a give photoperiod, while higher temperatures tend to avert or diminish the process. On the other hand, the low rates of diapause obtained at 18°C contradict this view. Nevertheless, high correlation was found between the laboratory evidence and field data, indicating the adaptability of the Israeli codling moth to subtropical climate.     

Flowering of Watsonia laccata as influenced by corm storage and forcing temperatures

The genus Watsonia, belonging to the family Iridaceae, is comprised of about 50 species including W. laccata (Jacquin) Ker Gawler that flowers from September to November following low temperature and winter rainfall. Therefore, we hypothesized that flowering would be favored by forcing at low greenhouse temperatures. Using clonal W. laccata corms, four experiments were designed to investigate the effect of temperatures during corm storage, forcing, and their interaction on growth and flowering. Corm formation is favored by growing plants at 18°–20°/15°–17 °C and 21°–23°/18°–20 °C, day/night temperatures. Flowering was earliest with corms produced at 24°–26°/18°–20 °C and forced at 18°–20/15°–17 °C, and was significantly delayed when forced at 27°–29°/24°–26 °C. Flowering was, however, favored by 2 or 4 weeks of high temperatures (27°–29°/24°–26 °C) prior to forcing at low temperatures (18°–20°/15°–17 °C). The number of florets was not significantly affected by corm storage, forcing temperatures, or their interaction, although forcing at high temperatures tends to reduce the floret number. Burn symptom at the tips of leaves was frequently observed, and further studies are required to understand the cause of the tip burn and how to correct the symptom.     

Temperature-induced alterations of in vivo chlorophyll a fluorescence induction in cucumber as affected by DCMU

Induction of chlorophyll a fluorescence and photosynthesis as affected by temperature were measured in cucumber leaf discs. Abrupt changes of the maximal variable fluorescence, Fv(p), and photosynthesis were observed around 9° and 21°C when the temperature was decreased from 30° to 0°C. The temperature-dependent maximal fluorescence of DCMU-treated leaf discs showed a single change around 21°C. Temperature-induced chlorophyll a fluorescence alterations are discussed in relation to electron transport activity of the two photosystems and photosynthetic activity of the cucumber leaf discs.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Fm maximal fluorescence - Fv(p) maximal variable fluorescence - qE energy-dependent fluorescence quenching - qQ Qa-dependent fluorescence quenching