Effects of Temperature on Germination of Peronospora parasitica Conidia and Infection of Brassica oleracea

The effect of temperature on germination of a South African isolate of Peronospora parasitica , and infection of Brassica oleracea was studied. The optimum condition for germination was 20° C at 100% relative humidity. The percentage germination obtained was 80–98% and 70–80% between 15 and 25° C at 100% relative humidity, after a 12 and 6h incubation period, respectively. Optimum temperature for germ tube growth was also 20° C. The temperature range for maximum infection of seedlings of a highly susceptible cabbage cultivar and subsequent disease development in vitro was 15–25° C and 90–100% infection was achieved after 48 h of incubation. At<15°C and 26–30° C infection percentage was decreased to 40–50% and 35–40%, respectively. No disease incidence was recorded at temperatures above 35° C. A scanning electron microscope study of the infection process showed that penetration of cotyledons by germ tubes was mostly via stomata and occasionally directly through the cuticle. Results are discussed in relation to the need for future studies of P. parasitica in South Africa.     

Seed dormancy in Rumex species in response to environmental factors

Abstract. Many Rumex species show similar seed dormancy characteristics but there is more information concerning R. crispus and R. obtusifolius than other species. These species respond positively to red or white light. Far-red light applied for short periods may promote or inhibit germination depending on the timing of the irradiation in relation to temperature change; but long periods of far-red inhibit germination. Seeds may also be stimulated to germinate in the dark by low-temperature stratification at 15°C or less providing the temperature of the seeds is subsequently raised to a minimum of about 15°C. Seeds can, however, germinate at lower temperatures providing they have received other appropriate stimulatory treatment. Seeds also respond to alternating temperatures. In a diurnal cycle the minimum upper temperature required is about 15°C and the maximum lower temperature is about 25°C. The optimum period spent at the upper temperature is about 8 h when it is 15–25°C but the optimum period decreases as the upper temperature is increased above this range so that at 45°C, for example, it is only about 30 min. The period spent at the lower temperature in a diurnal cycle is not critical. Providing these criteria are met, the percentage germination increases with the number and amplitude of the cycles. The warming part of the cycle is necessary for the response but so far there is no convincing evidence that cooling itself is important. Secondary dormancy is induced at constant temperatures at a rate dependent on temperature, but apparently only in the presence of oxygen. This feature affects the optimum timing of a temperature change or exposure to light. Strong positive interactions are shown between stimulatory temperature treatments and white or red light. Unlike many other weed species the seeds respond only slightly to nitrate ions. The implications of these responses are discussed in relation to field behaviour.     

Asymbiotic and symbiotic seed germination of Eulophia alta (Orchidaceae)—preliminary evidence for the symbiotic culture advantage

Eulophia alta (Linnaeus) Fawcett & Rendle seeds collected from the Florida Panther National Wildlife Refuge (Collier County, FL; FPNWR) were used in a screen of five asymbiotic orchid seed germination media to determine their effectiveness in promoting germination and protocorm development. In addition, 10 fungal isolates collected from the roots of E. alta at sites in the FPNWR, Highlands County (FL), and Goethe State Forest (Levy County, FL; GSF), and a fungal isolate from the roots of Spiranthes brevilabris collected from GSF were screened for their effectiveness at promoting in vitro symbiotic germination of E. alta seeds. After 18 weeks asymbiotic culture, seeds sown on PhytoTechnology Orchid Seed Sowing Medium germinated to a higher percentage (87.9%) and had a higher percentage of protocorms with developing protomeristems (32.7%) than seeds cultured on Knudson C, Malmgren Modified Terrestrial Orchid Medium, ?-strength Murashige & Skoog, or Vacin & Went Modified Orchid Medium. Significantly more leaf-bearing protocorms were observed on PhytoTechnology Orchid Seed Sowing Medium (0.8%) and Vacin & Went Modified Orchid Medium (1.3%) than other media tested. Of the fungi tested, one fungal isolate (Ealt-396) promoted germination to 69.0%, two isolates promoted germination to less than 0.75% and did not support further protocorm development, and eight isolates did not support germination. Seeds co-cultured in darkness with Ealt-396 grew more rapidly than asymbiotic seedlings following germination. In addition, co-cultured (=symbiotic) seedlings continued to develop more rapidly than asymbiotic seedlings upon transfer to 16/8 h light/dark photoperiod. Symbiotic seed culture of E. alta may be a more desirable method of propagation since protocorms develop more rapidly than seeds sown on asymbiotic media. Symbiotic seedlings may be more appropriate for reintroduction to natural areas than asymbiotic seedlings since symbiotic seedlings could serve to inoculate soils with a germination promoting mycobiont.     

Germination responses of a non-dormant seed population of Amaranthus patulus Bertol. to constant temperatures in the sub-optimal range

Abstract. The germination responses of a nondormant seed population of Amaranthus patulus Bertol, at constant sub-optimal temperatures in the range of 10–34°C were analysed through a detailed time-course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage, v. temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required 'thermal times' (θ), the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution and A is a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol⁻¹ with all 20–80% subpopulations.     

Effect of Temperature on the Formation of Microsclerotia of Verticillium dahliae

Microsclerotium formation by six isolates of Verticillium dahliae was studied at different temperatures both in vitro and in Arabidopsis thaliana . In vitro mycelial growth was optimal at 25°C, but microsclerotium formation was greatest at 20°C (two isolates) or 15–20°C (one isolate). Seedlings of A. thaliana were root-dipped in a conidial suspension, planted, and either placed at 5, 10, 15, or 25°C, or left at 20°C until the onset of senescence, after which some of the plants were placed at 5, 10, 15, or 25°C. The amount of microsclerotia per unit of shoot weight was assessed in relation to isolate and temperature. The optimal temperature for production of microsclerotia was 15–25°C. Two isolates each produced about 10 times more microsclerotia than each of the other four isolates. For these isolates, high R ²_adj.-values of 0.77 and 0.66 were obtained, with temperature and its square as highly significant (P   < 0.001) independent variables. R ²_adj.-values for the other isolates varied between 0.28 and 0.39. Moving plants to different temperatures at the onset of senescence led to microsclerotial densities that were intermediate between densities on plants that had grown at constantly 20°C and plants grown at other temperatures. This suggests that vascular colonization rate and rate of microsclerotium formation are similarly affected by temperature. The senescence rate of plants appeared unimportant except for plants grown at 25°C, which showed the highest amounts of microsclerotia per unit of plant weight in the most rapidly senescing plants.     

A mathematical model that uses Gaussian distribution to analyze the germination of Manfreda brachystachya (Agavaceae) in a thermogradient

Germination of nondormant seeds of Manfreda brachystachya (Agavaceae) was analyzed at temperatures ranging from 11–35°C. Maximum germination (95%) occurred at 25°C. An exponential sigmoid relationship was found between time and cumulative germination. Germination rate for every subpopulation (10–90% germination) was estimated by means of a normal distribution analysis. The kurtosis indicated die amplitude of the range of temperatures where the highest germination rates were concentrated, and the skew indicated sharply inhibitory temperatures in the range of temperatures used. Based on analysis of the normal distribution models for each subpopulation, we calculated a theoretical function which described germination rate over the temperature range considered: F(T,χ) = A × exp[−B(C−1)²], where A is the function that describes germination rate for each subpopulation (characterized by the percentage [χ] at optimal temperature); B is a shape parameter, 1/(σG²); and C is the ratio between each germination temperature (T) and the optimal germination temperature. The Gaussian curves were used to calculate thermal time, and base and ceiling temperatures. Germination thermal time ranged from 1 333 to 2 373°C h, and base and ceiling temperatures were 10.44 ± 0.7°C and 39.54 ± 0.7°C, respectively. There was a linear relationship between thermal time and cumulative percentage of germination of the subpopulations. Based on fitted curves for each subpopulation, the use of a general model for all the subpopulations has been proven: F8 = A × exp[−5.9437(C−1)²], where changes in the curves for each subpopulation depended on temperature only.     

A mathematical model that uses Gaussian distribution to analyze the germination of Manfreda brachystachya (Agavaceae) in a thermogradient

Germination of nondormant seeds of Manfreda brachystachya (Agavaceae) was analyzed at temperatures ranging from 11–35°C. Maximum germination (95%) occurred at 25°C. An exponential sigmoid relationship was found between time and cumulative germination. Germination rate for every subpopulation (10–90% germination) was estimated by means of a normal distribution analysis. The kurtosis indicated die amplitude of the range of temperatures where the highest germination rates were concentrated, and the skew indicated sharply inhibitory temperatures in the range of temperatures used. Based on analysis of the normal distribution models for each subpopulation, we calculated a theoretical function which described germination rate over the temperature range considered: F(T,x) = A × exp[-B(C−1)²], where A is the function that describes germination rate for each subpopulation (characterized by the percentage [x] at optimal temperature); B is a shape parameter, 1/(σ²); and C is the ratio between each germination temperature (T) and the optimal germination temperature. The Gaussian curves were used to calculate thermal time, and base and ceiling temperatures. Germination thermal time ranged from 1333 to 2373°C h, and base and ceiling temperatures were 10.44 ± 0.7°C and 39.54 ± 0.7°C, respectively. There was a linear relationship between thermal time and cumulative percentage of germination of the subpopulations. Based on fitted curves for each subpopulation, the use of a general model for all the subpopulations has been proven: F8 = A × exp[−5.9437(C−1)²], where changes in the curves for each subpopulation depended on temperature only.     

Germination Responses of Taraxacum platycarpum Seeds to Temperature

Abstract Germination responses of Taraxacum platycarpum seeds to temperature were examined under laboratory conditions to investigate the emergence-season choice mechanism of the seeds. Almost all the newly collected seeds were non-dormant. Under constant temperature conditions, maximum percentage germination (approximately 90%) was attained at temperatures 6–16°C, where simple linear relationships were observed between the temperature and the rates of germination, i.e. the reciprocals of the time taken to germinate by seed subpopulations with 10–80% germination. Thermal time required for germination of the subpopulations ranged from 600 Kh (degree Kelvin × hours) to 1500 Kh with a relatively constant base temperature of about 2.5°C. Lower limit temperature for germination was slightly below 6°C. Higher limit temperature for germination has the normal distribution with the mean ±SD of 19±2.5°C. Pre-exposure of imbibed seeds to temperatures higher than the higher limit temperature for germination, 25 and 30°C, had no effect on the germinability and the rate of germination at a circa-optimum temperature. Moist chilling treatment at 4°C caused an increase in the variation of germination rate within the seed population, but no evidence for dormancy-inducing or breaking effects was obtained.     

Effect of temperature and water activity on in vitro germination of Monilinia spp.

Aims:  This study evaluated the effect of temperature (0–38°C) and water activity ( a _w: 0·87–0·99) on the lag phase prior to germination and the percentage of germination over time for Monilinia laxa , Monilinia fructicola and Monilinia fructigena .
Methods and Results:  More than 80% of viable conidia germinated at 25°C and 0·99 a _w within 2 h for M. fructicola and M. fructigena and 4 h for M. laxa . There was no germination at 38°C, and all three Monilinia spp. germinated at 0°C. At the lowest a _w (0·87), none of the Monilinia spp. was able to germinate at any of the incubation temperatures studied. Whereas at 0·90 a _w, conidia were only able to germinate at 15, 25 and 30°C for the three species studied, except for M. fructicola at 15°C. In contrast, at 0·95, 0·97 and 0·99 a _w, germination occurred at all studied temperatures less 38°C. Generally, the lag phase was longer at low levels of a _w (0·90–095), and differences were more evident as temperatures were far from the optimum (0–5°C).
Conclusions:  Germination and lag phase period were markedly influenced by temperature and a _w, and in general when conditions of temperature and a _w were suboptimal, the lag phase was longer and the percentage of germination was lower.
Significance and Impact of the Study:  Knowledge of the germination requirements of this fungus is important in order to understand their behaviour in natural situations and to provide baseline data required for the construction of new prediction models. Our study might be used to develop a predictive model to understand and control the disease caused by Monilinia spp.     

Light and temperature action in germination of seeds of the empress tree (Paulownia tomentosa)

Seeds of the empress tree ( Paulownia tomentosa Steud.) were imbibed for two weeks in darkness at constant temperatures (18, 23 or 28°C), and then irradiated with red light for 5 min. Germination was poor if it took place at the same temperature as imbibition, but a high percentage was achieved if the seeds were exposed to higher or lower temperatures before they were irradiated. Maximum germination was obtained when the difference between pretreatment and imbibition was about 10°C. The effect increased with the duration of the pretreatment and was optimal at 24 h. The effect decreased as the time lapse between temperature pretreatment and red light irradiation increased, and it was lost after two days. If pretreatment was shorter than 24 h (12 h). a high percent of germination was obtained by alternating pretreatment and imbibition temperatures. The germination of seeds imbibed in 40% heavy water was also stimulated by temperature pretreatments. Light and temperature also exhibited an interactive effect in the germination of seeds that were imbibed in darkness for only 3 days. For each of the germination phases there was a temperature at which the time needed for 50% germination was the shortest, namely 35°C during imbibition, 37.5°C in the period of P_fr activity. and 32.5°C during radicle protrusion. The data obtained are shortly discussed in relation to the domestication of empress tree in Southern Europe.     

Characteristics of alternating temperatures which stimulate loss of dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Abstract. Alternating temperatures stimulate the germination of Rumex crispus L. and Rumex obtusifolius L. The optimum period spent at the lower temperature in a diurnal cycle is greater than that spent at the higher temperature. Under most conditions the optimum period at the upper temperatures is about 8 h but, as the upper temperature of a cycle is increased, the optimum period at the upper temperature becomes shorter and more critical. Thus when it is 35°C the optimum period is 2.5–4 h in the light, or about 1 h in the dark. The effect of alternating temperatures is much less in the dark than in the light and in general only extreme alternations with short periods at the higher temperature are effective in the dark. In the light any temperature alternation within the range 1–35°C is effective to at least some extent, providing the temperature difference is 5°C or more and providing the alternation includes one temperature which is above approximately 15°C and one which is below approximately 25°C. The optimum temperature difference is about 15°C. In the light, 4 to 10 cycles saturate the response, but in the dark, where the effect is much less, the response may not be saturated even by 16 cycles. KNO₃ at 10⁻³ M has little effect on the response to alternating temperatures either in the light or the dark. The response to alternating temperature regimes does not appear to vary in quality, i.e., in terms of which particular treatments are best, but it varies in magnitude with site and year of seed collection; and it increases slowly during dry storage, even when stored at a temperature as low as 1.5°C.     

温度变化对油菜及其伴生杂草种苗生长和幼苗生理特性的影响

以目前大面积栽培的甘蓝型油菜(Brassica napus) ‘秦优10号’和其田间常见的8种杂草播娘蒿(Descurainia sophia)、泽漆(Euphorbia helioscopia)、野燕麦(Avena fatua)、棒头草(Polypogon fugax)、婆婆纳(Veronica didyma)、看麦娘(Alopecurus aequalis)、灰绿藜(Chenopodium glaucum)、反枝苋(Amaranthus retroflexus)为试验材料, 利用人工气候培养箱控温, 研究了10 ℃/5 ℃ (昼/夜)、18 ℃/10 ℃、25 ℃/20 ℃、35 ℃/30 ℃、40 ℃/35 ℃不同温度幅度处理对它们的发芽势、发芽率、幼苗形态及生理指标的影响, 旨在为预测气候变化环境下油菜田恶性靶标杂草的演替趋势提供参考依据。试验结果表明: 不同供试杂草对温度变化表现出明显的适应性差异, 看麦娘、灰绿藜和反枝苋的最适萌发温度偏高, 如反枝苋在高温处理(40 ℃/35 ℃)下种子的发芽率达到最高(91%); 而播娘蒿、泽漆、野燕麦、棒头草、婆婆纳种子的最适萌发温度主要集中于10-18 ℃范围内。进一步测试研究表明, 高温处理(40 ℃/35 ℃)下, 反枝苋幼苗生长旺盛, 体内丙二醛的积累也明显低于低温(10 ℃/5 ℃)处理, 可溶性糖和可溶性蛋白含量以及保护酶活性也较高, 表明反枝苋对高温胁迫有较好的适应性, 灰绿藜对高温的响应与反枝苋相似, 在高温气候年份, 要严防这2种草害加重; 而在低温处理(10 ℃/5 ℃)下, 野燕麦的种子萌发率达到100%, 其幼苗生长旺盛, 体内可溶性糖和可溶性蛋白含量及保护酶活性较高, 播娘蒿对低温胁迫的响应类似于野燕麦, 因此在寒冷年份需加强对野燕麦和播娘蒿草害的预防。供试油菜品种相对于所有供试杂草对温度变化的适应性更好, 其种子在不同温度处理下均保持较稳定的高发芽率, 且幼苗长势良好, 表明‘秦优10号’是一个对温度变化适应性很好的油菜品种。     

A butenolide, isolated from smoke, can overcome the detrimental effects of extreme temperatures during tomato seed germination

The butenolide, 3-methyl-2H-furo[2, 3-c]pyran-2-one, is an highly active compound isolated from plant-derived smoke. This compound is known to stimulate seed germination in a wide range of plants akin to smoke or aqueous extracts of smoke. The present study attempted to elucidate the role of the butenolide in overcoming detrimental effects of low and high temperatures on tomato seed germination and seedling growth. The germination percentage followed a parabolic curve for temperatures ranging from 10 to 40°C, with 25°C being the optimum for all treatments. Control seeds showed radicle emergence at two extreme temperatures (10 and 40°C) and seedlings failed to develop further, even upon prolonged incubation. By comparison the butenolide-treated seeds grew into phenotypically normal seedlings at these non-optimum temperatures. The smoke–water-treated seeds had an intermediate response as only a fraction of germinated seed developed into normal seedlings. Seedling vigour indices as well as seedling weight were significantly higher (p ≤ 0.05) for butenolide-treated seeds at all temperatures. Furthermore, seedlings developed in the presence of the butenolide had about a 1:1 correspondence between root and shoot length. Butenolide-treated seeds grew better than the control seeds in the temperature shift experiments. A gradual decline in the vigour index values was recorded with an increased duration of incubation at the extreme temperatures. Results of the present study are very important from an horticultural point of view as they indicate the potential use of the butenolide compound in restoring normal seed germination and seedling establishment in tomato below and above optimum temperatures.     

Effects of temperature on the growth and survival of the European eel, Anguilla anguilla L.

Experiments to determine the growth rate of eels ( Anguilla anguilla L.) at different temperatures are described and show the optimum temperature for growth to be 22–23° C. The ultimate upper lethal temperature was found to be 38° C and the critical thermal maximum varied from 33 to 39° C for fish acclimated at 14 to 29° C. An attempt was also made to determine lower lethal temperatures. Eels enter a state of torpor at temperatures varying from 3° C for fish acclimated at 29° C to less than 1° C for fish acclimated at 23° C or below. The results have been used to estimate the growth rates expected from eels cultured in power station cooling water using different types of temperature control.     

Germination responses of Reaumuria vermiculata to salinity and temperature

Reaumuria vermiculata is a xerohalophytic perennial dwarf shrub distributed in many gypseous and saline areas in southern Tunisia. A laboratory experiment was carried out to assess the effects of temperature and salinity on germination. The germination responses of the seeds in darkness were determined under a range of salinity and temperature regimes. Temperatures between 10°C and 30°C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or a decrease in temperature from the optimal temperature (15°C). Highest germination percentages were obtained under non-saline conditions and increases in salinity inhibited seed germination. Salt stress decreased both the germination percentage and the germination speed (increase of the mean time to germinate). Seed germination decreased with an increase in NaCl concentrations at all temperatures. An interaction between salinity and temperature yielded no germination at salinity of 300 mM, whereas some seeds germinated under the optimal temperature.     

Suboptimal temperature favors reserve formation in biennial carrot (Daucus carota) plants

In response to suboptimal temperatures, temperate annual plants often increase root:shoot ratios, build-up carbohydrates and display typical morphological and anatomical changes. We know less about the responses of biennials such as carrot. As a model plant, carrot has the additional feature of two functionally and morphologically distinct root parts: the taproot, which stores carbohydrate and other compounds, and the fibrous root system involved in acquisition of water and nutrients. Here, we analyze the effects of temperature (12 vs 25°C) on growth, carbohydrate accumulation and whole-plant morphology in two carrot cultivars. Our working hypothesis is that suboptimal temperature favors active formation of reserve structures, rather than passive accumulation of storage carbohydrates. In comparison with plants grown at 25°C, plants grown at 12°C had: (1) higher fibrous root:shoot ratio (13%) , (2) thicker (10–15%) and smaller (up to two- to three-fold) leaves, (3) lower leaf cuticular permeance (two- to four-fold), (4) higher taproot:shoot ratio (two-fold), (5) higher phloem:xylem ratios in taproot (two- to six-fold), (6) unchanged percentage dry matter content (%DMC) in leaves, petioles or fibrous roots and (7) higher %DMC in taproot (20%). However, %DMC of individual taproot tissues (phloem and xylem) was unaffected by temperatures and was consistently higher in the phloem (up to 30%). Therefore, the higher %DMC of whole taproots at 12°C was attributed solely to the increased development of phloem tissue. Carrot, therefore, shares many of the most conspicuous elements of temperate plant responses to low temperatures. Consistently with our hypothesis, however, carrots grown at suboptimal temperature promoted reserve structures, rather than the increase in carbohydrate concentration typical of most temperate annual species and woody perennials.     

Germination responses of four native terrestrial orchids from south-west Western Australia to temperature and light treatments

We report an investigation into the impact of temperature and illumination on in vitro symbiotic and asymbiotic germination of the threatened taxon Caladenia huegelii, and three other orchid spp. namely—Caladenia latifolia, Microtis media and Pterostylis sanguinea, all species from south-west Western Australia, a recognized biodiversity hotspot. High symbiotic germination on oatmeal agar (OMA + fungal symbionts specific to each species) was recorded in three species in continuous dark incubation i.e. C. huegelii seeds (98 % germination at 25 °C), and M. media and P. sanguinea (93 and 98 % respectively at 20 °C). Highest symbiotic germination for C. latifolia (100 %) was observed at 15 and 20 °C under light treatment (12/12 h light/dark). Low temperature incubation (10 °C) significantly suppressed symbiotic germination/development of seedlings across all species. Asymbiotic media treatments assessed (OMA minus fungal symbionts, Pa₅ and ½ MS), failed to stimulate any germination with C. latifolia seeds at 20 °C in either light or dark treatments after an 8 week incubation period. Seeds of M. media sown onto ½ MS medium resulted in higher germination in all developmental stages (3–5) in dark treatment than OMA and Pa₅. Seeds of P. sanguinea sown onto ½ MS medium resulted in higher overall germination in all developmental stages (3–5) in light and dark incubation compared to OMA and Pa₅. OMA supported the highest asymbiotic germination (100 %) in both light and dark incubation with M. media (only to stage 3) but did not support germination and development with other spp. tested. Caladenia huegelii seeds reached developmental Stage 3 (i.e. germinated), but only on Pa₅ medium and only at a relatively low rate in either light (2.6 %) or dark (2.1 %). Germination was higher and development of seedlings faster overall in all test species in symbiotic compared with asymbiotic media treatments. P. sanguinea seeds demonstrated the best response (among species tested) to asymbiotic germination on ½ MS with 40–53 % of germinated seeds spread over developmental stages 3–5 in light or dark incubation (at 20 °C) respectively. Illumination had no effect on fungal symbiont growth across all species, however incubation temperature treatments (10, 15, 20 and 25 °C) affected fungal growth rate. Growth of the fungal symbionts of C. huegelii, M. media and C. latifolia demonstrated significantly lower activity at 10 °C, but the cumulative radial growth rate of the P. sanguinea fungal symbiont reached 64 cm² after only 2 weeks at all temperatures tested, including 10 °C. The study highlights differences in symbiotic and aysmbiotic germination and early protocorm development in vitro between co-occurring herbaceous terrestrial Australian orchid taxa in response to variations in basal media, temperature and light.     

The effect of temperature on the life cycle, growth and fecundity of Branchiura sowerbyi (Oligochaeta: Tubificidae)

Branchiura sowerbyi Beddard was probably introduced to Britain with exotic plants consigned to botanic gardens. The British populations occur mainly in artificially warmed habitats such as lily ponds in botanic gardens and power station effluents but a few are found at natural temperatures.
Branchiura completed its life cycle in about a year both in the river Avon, Wiltshire, at natural temperatures and in the warm effluent from a power station discharging into the river Thames. In a worm culture maintained at natural temperatures the rate of cocoon production reached a peak in summer and was closely related to temperature.
In the laboratory it was found that the optimum temperature for cocoon laying in mature worms, also growth in sexually immature worms, was near 25°C. The optimum temperature for growth in sexually mature worms, however, was lower (10°C in the Avon population and 15°C in the Thames population). It followed that at 20°–25°C the growth of sexually mature worms was probably depressed by the high rate of cocoon production.     

The Effects on Temperature on Growth in vitro of Pseudomonas syringae and Xanthomonas pruni

Growth rates in vitro of Pseudomonas syringae and Xanthomonas pruni were measured over the temperature range 0–36 °C. The estimated temperature optimum for X. pruni was 31 °C, with a doubling time of 1.53 h. The estimated temperature optimum for P. syringae was 28 °C with a doubling time of 1.27 h, although analysis showed no significant difference in the doubling times over the range 23–33 °C, indicating an unusual plateau at the maximum rate of growth of this organism. P. syringae and related plant pathogenic Pseudomonas spp. grew well at low temperatures, but X. pruni did not. Cultures of P. syringae and X. pruni had a very short lag phase after their incubation temperature was changed from 4 °C to a temperature close to their optimum (29 °C). When the incubation temperature of these organisms was changed from 11.5–29 °C, X. pruni grew without a lag phase at the rate expected for the higher temperature. However, the initial growth rate of P. syringae at the higher temperature was significantly greater than that at which the organism subsequently developed. The ecological significance of these points is discussed. The usefulness of the Arrhenius coefficients as characteristics of these organisms is discussed.     

Adaptation to sub- and supraoptimal temperatures of inbred maize lines differing in origin with regard to seedling development and photosynthetic traits

Six inbred lines of maize ( Zea mays L.) from cool temperate regions (C) and from warm regions (W) were grown at 14, 22, 30 and 38°C up to the same physiological age, the full expansion of the third leaf. Generally, plants developed smaller shoot dry weights and leaf areas at extreme temperatures. The shoot:root ratio was lowest at 22°C and highest at 30°C. Most lines had a minimum for specific leaf dry weight at 30°C, but W lines had a second lower minimum at 14°C. Phosphofructokinase activity scarcely reacted to temperature between 22° and 38°C; at 14°C one C line and all W lines had rather low activities. Generally, the chlorophyll content increased steeply from 14 to 22°C and decreased somewhat from 30 to 38°C. In C lines the carotenoid level decreased from 14 to 38°C. No uniform temperature response was found for PEP carboxylase activity, but the highest activity was mostly attained at 38°C. RuBP carboxylase activity increased considerably from 14 to 22°C and remained comparatively constant at higher temperatures. The highest activity of NADP malate dehydrogenase was found at 22°C, with a decrease up to 38°C and with second lowest values at 14°C. C lines possessed larger leaf areas, shoot dry weights and higher shoot:root ratios than W lines at 14 and 22°C, and higher specific leaf dry weights over the whole temperature range. The genotypic pattern of shoot dry weight at 14°C corresponded reasonably well with that of phosphofructokinase activity. A better adaptation of C lines to suboptimal temperatures was mostly clearly indicated for photosynthetic traits which have a well proven relationship with the chloroplast membranes: chlorophyll, carotenoids and RuBP carboxylase. The least distinct effects of origin were observed at 38°C; a tendency prevailed for a better performance of C lines with regard to phosphofructokinase, carotenoids, RuBP carboxylase and NADP malate dehydrogenase.