Alternating Temperature Regimes Research Articles

Seed germination and survival of the endangered psammophilousRouya polygama(Apiaceae) in different light, temperature and NaCl conditions

AbstractRouya polygama(Apiaceae) is an endangered Mediterranean species of great phytogeographical and ecological interest, growing on coastal sandy dunes. Intraspecific variability in the responses to constant temperatures (5–25°C) and an alternating temperature regime (25/10°C), salt stress (0–600 mM NaCl) and recovery of seed germination was evaluated among six populations from Sardinia and Corsica. Seeds were non-dormant and germination percentages ranged from 10 to 83%, depending on temperature and population. Differences in germination percentages were mainly due to different seed mortality among seed lots.R. polygamaseeds germinated in salt concentrations up to 200 mM NaCl, whereas higher salt concentrations totally inhibited germination. Salt affected seed viability, and the recovery response decreased with increasing salinity and temperature. Inter-population variability and different sensitivity to NaCl in seed germination were detected. Our results are consistent with field germination in a period from autumn to spring, when water is available in the soil and temperatures are not prohibitive for seedling establishment, representing an advantageous ecological adaptation for seedling establishment to the unpredictable Mediterranean rainfall pattern. Further studies onR. polygamaare needed to investigate germination requirements at temperatures higher than 25°C and its germination in the field, and to clarify genetic inter-population variability, considering a higher number of populations and possibly extending to North African populations.

Germination shifts of C3 and C4 species under simulated global warming scenario.

Research efforts around the world have been increasingly devoted to investigating changes in C3 and C4 species' abundance or distribution with global warming, as they provide important insight into carbon fluxes and linked biogeochemical cycles. However, changes in the early life stage (e.g. germination) of C3 and C4 species in response to global warming, particularly with respect to asymmetric warming, have received less attention. We investigated germination percentage and rate of C3 and C4 species under asymmetric (+3/+6°C at day/night) and symmetric warming (+5/+5°C at day/night), simulated by alternating temperatures. A thermal time model was used to calculate germination base temperature and thermal time constant. Two additional alternating temperature regimes were used to test temperature metrics effect. The germination percentage and rate increased continuously for C4 species, but increased and then decreased with temperature for C3 species under both symmetric and asymmetric warming. Compared to asymmetric warming, symmetric warming significantly overestimated the speed of germination percentage change with temperature for C4 species. Among the temperature metrics (minimum, maximum, diurnal temperature range and average temperature), maximum temperature was most correlated with germination of C4 species. Our results indicate that global warming may favour germination of C4 species, at least for the C4 species studied in this work. The divergent effects of asymmetric and symmetric warming on plant germination also deserve more attention in future studies.

Effects of salinity, temperature, and polyethylene glycol on the seed germination of sunflower (Helianthus annuus L.).

Salinization has severe influences on agriculture in the whole world. The main aims of this work were to evaluate osmotic effect and ion effect of NaCl on seed germination of three sunflower (Helianthus annuus L.) cultivars interacting with three alternating temperature regimes and to select the most salt tolerant cultivars to plant in the saline region. Seeds were germinated in the isotonic NaCl and polyethylene glycol (PEG) solutions of −0.45, −0.90, −1.34, −1.79, and −2.24 MPa at 10 : 20, 15 : 25, and 20 : 30°C temperature regimes. Both NaCl and PEG inhibited germination, but the effects of NaCl were less as compared to that of PEG, which means that adverse effects of PEG on germination were due to osmotic effect rather than specific ion accumulation. For the three cultivars, higher germination occurred at 10 : 20°C in NaCl treatments and at 20 : 30°C in the isotonic PEG treatments. Among the three cultivars, Sandaomei (SDM) is the most tolerant to salt and PEG stress.

Germination of mucilaginous seeds of Plantago albicans (Plantaginaceae): effects of temperature, light, pre-sowing treatments, osmotic stress and salinity

Plantago albicans L. (Plantaginaceae) is a perennial herbaceous plant widely distributed throughout the Mediterranean region. The germination requirements (under different controlled conditions of light and temperature, and after two pre-sowing treatments) and tolerance to osmotic stress (polyethylene glycol, PEG 6000) and salinity (NaCl) of P. albicans seeds were studied. Seeds were germinated under constant temperatures (5°C, 10°C, 15°C, 20°C, 25°C and 30°C) and alternating temperature regimes of 20/10°C and 25/15°C with a 16 h/8 h light/dark photoperiod. The outer layer of seeds become mucilaginous when wetted and the presence of mucilage on seeds significantly increased germination percentages at all temperatures tested. P. albicans seeds were non-dormant and temperature significantly affected germination percentages and germination rate (germination velocity expressed as mean germination time, MGT). The final germination percentages ranged from 34% to 89% for intact seeds (seeds with mucilage) and from 9% to 62% for demucilaged seeds, depending on the temperature. Temperatures of 25°C and 25/15°C gave the highest germination percentages. Light did not affect seed germination at both temperature regimes assayed (25°C and 25/15°C). Germination percentages of seeds soaked for 24 h in distilled water or in a gibberellic acid (GA3) solution were not significantly higher than that of untreated seeds. In general, both the final germination percentage and germination rate were reduced by increasing salinity and PEG concentration. Seeds germinated in up to 35% PEG and 300 mmol·L–1 NaCl. Recovery of germination for seeds when transferred to distilled water after being in PEG or salinity treatments for 15 days was quite high, suggesting that P. albicans seeds are tolerant to osmotic and salt stresses.

Ecology of Musk Thistle (Carduus nutans) Seed Germination for Grasslands of Temperate Climates

Musk thistle is an invasive weed that is widely distributed throughout much of North America, including grasslands in temperate climates of the midwest USA. A series of laboratory and greenhouse experiments were conducted to determine the effect of various environmental factors on germination of musk thistle seeds. In temperature-fluctuation experiments, seed germination was greater than 65% in both alternating (30/20 C) and constant (20 or 25 C) temperature regimes with an 8-h day but less (33%) in warmer regimes (35/20 C). Germination of musk thistle seeds was 37% in alternating temperature regimes of 30/20 C in total darkness, but less than 67% in pots in the greenhouse. Differences of 10 and 15 C between day and night temperatures resulted in 91 and 75% maximum germination of musk thistle, respectively. Increasingly dryer soils reduced germination of musk thistle seeds from 35% (−0.03 MPa) to 0% (−1.2 MPa), whereas saline soils (> 80 mM) reduced maximum germination to less than 10%. Musk thistle seeds collected from populations in a bare-ground area had 96% germination, which was greater than that of seeds collected from populations growing in a perennial grass pasture (71%). A residence time (i.e., period that seeds remained on the parent plant) of 9 to 12 wk after capitulum maturity resulted in seeds germinating more quickly than those dispersed earlier. Overall, reduced light levels, cool and fluctuating temperatures, and amount of time seeds remained in residence are some of the most important factors that contribute to germination of musk thistle seeds. Information on germination dynamics of musk thistle seeds provides an understanding of the interactions that affect this process and underscores the importance of timely management strategies in temperate grasslands.

Constant and Alternating Temperature Effects on Seed Germination Potential in Artemisia annua L

Artemisinin is a sesquiterpene lactone with a peroxide bridge, and it is a natural anti-malarial drug obtained from Artemisia annua L. High germination percentages and rates are essential for commercial growers of this species to justify buying premium-priced seed to ensure high performance of their crop. The objective of our research was to determine the seed germination potential of A. annua variety ‘CIM-Arogya.’ An experiment was conducted using three constant (15°C, 20°C, and 25°C) and three alternating (20/15°C, 25/15°C, and 20/25°C) temperature regimes. Seed germination was evaluated in Petri dishes lined with filter paper under daily 16 h light and 8 h dark photoperiod. The highest estimates of mean percentage germination (82.0) and germination energy (20.5) were observed at 15°C, followed by 20/15°C (74.5% germination and 18.6% germination energy). Further, the 3 to 5-day period after seed sowing was ideal for the first germination count, and the 7 to 8-day period after sowing was best for final germination count. Day 7 was best for final germination determination at both constant and alternating temperature regimes. Thus, growers should sow seeds when the mean temperature is 15–20°C for about 7 days.

Alternating temperatures affect life table parameters of Phytoseiulus persimilis, Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari: Tetranychidae)

Increasing energy costs force glasshouse growers to switch to energy saving strategies. In the temperature integration approach, considerable daily temperature variations are allowed, which not only have an important influence on plant growth but also on the development rate of arthropods in the crop. Therefore, we examined the influence of two constant temperature regimes (15 °C/15 °C and 20 °C/20 °C) and one alternating temperature regime (20 °C/5 °C, with an average of 15 °C) on life table parameters of Phytoseiulus persimilis and Neoseiulus californicus and their target pest, the two-spotted spider mite Tetranychus urticae at a 16:8 (L:D) h photoperiod and 65 ± 5 % RH. For females of both predatory mites the alternating temperature regime resulted in a 25-30 % shorter developmental time as compared to the corresponding mean constant temperature regime of 15 °C/15 °C. The immature development of female spider mites was prolonged for 7 days at 15 °C/15 °C as compared to 20 °C/5 °C. With a daytime temperature of 20 °C, no differences in lifetime fecundity were observed between a nighttime temperature of 20 and 5 °C for P. persimilis and T. urticae. The two latter species did show a higher lifetime fecundity at 20 °C/5 °C than at 15 °C/15 °C, and their daily fecundity at the alternating regime was about 30 % higher than at the corresponding mean constant temperature. P. persimilis and T. urticae showed no differences in sex ratio between the three temperature regimes, whereas the proportion of N. californicus females at 15 °C/15 °C (54.2 %) was significantly lower than that at 20 °C/5 °C (69.4 %) and 20 °C/20 °C (67.2 %). Intrinsic rates of increase were higher at the alternating temperature than at the corresponding mean constant temperature for both pest and predators. Our results indicate that thermal responses of the studied phytoseiid predators to alternating temperature regimes used in energy saving strategies in glasshouse crops may have consequences for their efficacy in biological control programs.

Effects of cold stratification and dry storage at room temperature on seed germination of eight desert species from the Hexi Corridor of China

Aims We investigated seed germination of eight desert plant species of the Hexi Corridor of China following cold-wet stratification and dry storage at room temperature to better understand seed germination and dormancy characteristics and how these species are adapted to their habitat. Methods Seed viability and initial germination percentage of Glycyrrhiza uralensis, Sphaerophysa salsula, Peganum multisectum, Zygophyllum fabago, Nitraria tangutorum, Lycium ruthenicum, Salsola ruthenica and Asterothamnus centrali-asiaticus were determined. Then seeds of these species were divided into four groups (I, II, III and IV) and stored in a refrigerator ((4 ± 1) °C, moist), cold room in winter ((–5 ± 1) °C, moist), outdoor in winter ((–26 – 10) °C, moist) and room temperature ((20 ± 1) °C, dry) for 60 d. Germination was determined under a constant (20 °C) and an alternating temperature regime (25 °C / 10 °C) with 12 h photoperiod (light/dark) for 30 d. Two main germination indices including germination percentage and T50 (half germination time) were recorded. Data were analyzed by one-way ANOVA and the least significant difference test (LSD) at 5% level. Important findings There were three types of seed responses to cold-wet stratification: germination percentage increased, no change, or decreased. Germination percentage of seeds of P. multisectum and Z. fabago significantly increased following cold-wet stratification of 4 °C and –5 °C, and partially increased following –26 – 10 °C. Germination percentage of seeds of L. ruthenicum significantly increased following 4 °C, –5 °C, –26–10 °C and dry storage at room temperature, with germination of 90%–100%. Seeds of P. multisectum, Z. fabago and L. ruthenicum have slight physiological dormancy. Germination of seeds of N. tangutorum, G. uralensis and Sphaerophysa salsula slightly changed following three cold-wet stratification. Seeds of Salsola ruthenica with non-dormancy (germinated to 84% before storage) decreased their germination following cold-wet stratification of 4 °C, whereas no change occurred at –5 °C, –26 – 10 °C. In addition, the response of germination to incubation temperature varied with species.

From seed to seedling: A critical transitional stage for the Mediterranean psammophilous species Dianthus morisianus (Caryophyllaceae)

Seed germination, seedling emergence and seed persistence in the soil were investigated for Dianthus morisianus (Caryophyllaceae), a psammophilous endemic species of Sardinia. Stored and freshly collected seeds were incubated in a range of constant temperatures (5–25°C) and an alternating temperature regime (25/10°C). The effect of seed burial depth on seedling emergence was investigated under controlled environmental conditions. Seed persistence in the soil was verified by in situ experimental seed burials. Seeds of this species were non-dormant, and all seed lots germinated both in the light and darkness, mainly at low temperatures (≤20°C), with a maximum at 15°C (≥95%). Optimal seedling emergence was obtained when seeds were buried at a depth of 1–2 cm, and a declining emergence with increasing depth was observed. D. morisianus was also unable to form a persistent soil seed bank. The fate of the seeds that, after dispersal, do not emerge from the soil in the spring is, therefore, presumably to die before the next favourable growing season.

Seed Germination and Seedling Growth of the Endangered Azorean Cherry Prunus azorica

Prunus azorica is an Azorean endemic tree considered as a priority species for conservation. It is important as a laurel forest component, particularly at medium altitude, and as a food source for the endangered bird Pyrrhula murina. The best conditions for seed germination were investigated after removal of the outer layers of the fruit by determining the effect of 1) using stones or seeds; 2) stratification regime (six treatments and a control); 3) incubation temperature (four alternating temperature regimes); and 4) gibberellic acid concentration (three levels). This resulted in a fully factorial design with 168 (2 × 7 × 4 × 3) treatments with three replicates per treatment and 25 seeds per replicate. Cumulative germination percentages were determined at the end of the trial. Globally, there was a significant effect of endocarp removal (49% germination with seeds and 15% with stones). Both for stones and seeds, there was a significant effect of incubation temperature, stratification regime, and growth regulator concentration. Stones attained a maximum germination of ≈80% under several stratification treatments including cold (4 °C) or warm (20 °C) followed by cold and at 10/5 °C without the addition of a growth regulator. Seeds attained a maximum germination of greater than 90% without stratification at 10/5 or 15/10 °C without the addition of a growth regulator. During the stratification process, germination occurred only for seeds, particularly for longer treatments, for example, those corresponding to 3 or more months of stratification, including warm followed by cold (75% to 80%) or cold alone (77%). According to seed morphology and germination results, the seed appears to have a non-deep physiological dormancy. Seeds of P. azorica can thus be efficiently germinated after endocarp removal at temperatures of 10/5 or 15/10 °C with a daily light period of 12 hours. This protocol allowed producing hundreds of viable seedlings that were used in the reforestation of a laurel forest stand in a LIFE project.

Effects of thermophotoperiod on growth parameters of Helicoverpa armigera

AbstractThe effects of photoperiod and temperature on growth parameters of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were investigated under laboratory conditions by exposing its larvae to fluctuating and alternating temperature regimes. Our data made evident that the interplay between photoperiod and temperature has a direct effect on growth parameter responses of H. armigera. However, the type of temperature regime (fluctuating or alternating) may enhance or diminish the effects of photoperiod. With fluctuating temperature, larval developmental time was significantly reduced with increasing photophase, irrespective of the diapause status later in the pupal stage; the lowest value was observed under continuous light conditions. With alternating temperature, larval developmental time was significantly decreased with the reduction in temperature amplitude, and with the coincidence of the thermophase with the scotophase. At both temperature regimes, no significant differences in pupal weight were observed between diapausing and non‐diapausing individuals, although, in most treatments, the diapausing pupae tended to be heavier than the non‐diapausing ones. The increased pupal weight of individuals destined for diapause is probably related to their longer larval developmental time. Knowing the effects of these factors on the variation of H. armigera growth is necessary in explaining phenomena associated with immature stages, and can lead to a more profound understanding of the potential for this insect to evolve in response to environmental changes.

Water and Temperature Stress Impact Fitness of Acetohydroxyacid Synthase–Inhibiting Herbicide-Resistant Populations of Eastern Black Nightshade (Solanum ptychanthum)

Many substitutions in the herbicide target enzyme acetohydroxyacid synthase (AHAS) confer whole-plant resistance and may reduce plant fitness. This study was done to determine the impact of different watering and temperature regimes on the germination, growth, and seed production of eastern black nightshade populations resistant (R) to AHAS inhibitors as conferred by an Ala205Val substitution in their AHAS. Growth and reproductive ability of four R and four susceptible (S) populations were determined in growth-cabinet and greenhouse studies. The R populations had lower total berry and viable seed production per plant than S under optimal conditions because of slower berry maturation. Seed production of both S and R populations decreased under lower or higher than optimal watering regimes; however, this reduction was more pronounced for the S populations so that seed production was comparable across S and R. The R populations had significantly higher germination and vegetative growth under cooler alternating temperature regimes. Although there were no differences between R and S plants under stress conditions, under optimal growth conditions, the Ala205Val substitution comes at a significant cost in eastern black nightshade. Under optimal growth conditions and in the absence of herbicide selection, S populations should eventually dominate over R; however, the lack of fitness differences under stress conditions could enhance the persistence of the R individuals.

Opportunistic Germination Behaviour of Gypsophila (Caryophyllaceae) in Two Priority Habitats from Semi-arid Mediterranean Steppes

Gypsophila tomentosa and G. struthium are closely related species, characteristic of two European priority habitats, salt and gypsum inland steppes, respectively. Germination strategies of the two taxa were investigated in plants from two nearby populations, growing under the same climatic conditions but on different types of soil, and belonging to different plant communities. Their germination patterns were studied at five constant temperatures in darkness: 5oC, 10oC, 15oC, 20oC and 25oC, and the base temperature and the thermal time requirement were calculated. As the distribution area of both species is subjected to a Mediterranean continental climate with significant differences between day and night, the possible preferences for an alternating temperature regime (25/10oC) were contrasted, as well as the influence of cold stratification and freezing. The effects on seed germination of light at constant 20oC and a 12/12 h photoperiod were also compared in the two species. The main conclusions of the work are the similarity of behaviour of both species, with an absence of seed dormancy, their opportunistic germination strategy, and water availability as the principal limitation to seed germination and plant establishment. The base temperature and thermal time indicate higher competitiveness of G. struthium at low temperatures, but seed germination of G. tomentosa is the most efficient at temperatures higher than 13.3oC. Optimal temperature and illumination conditions for nursery propagation depend on the species. The high viability of seeds observed after freezing prove the orthodox character of these seeds, providing additional information for long term seed conservation procedures.

Germination résponses of Khaya anthotheca seeds to a range of alternating and constant températures provided by the 2-way Grant’s thermogradient plate

Khaya anthotheca seeds were placed in Petri dishes containing a gel of 1% water agar for germination over a period of 30 consecutive days. Petri dishes were arranged 8 units x 8 units on the 2-way Grant’s thermogradient plate (a bi-directional incubator). The goal of the study was to take a more comprehensive look at germination responses of seeds to a broad range of alternating or constant temperatures on the thermogradient plate. The instrument allows for germination testing of seeds over a wide range of single temperature and alternating temperature regimes over a time continuum, given 64 temperature combinations (regimes) (5 to 40°C). Conditions were 40/40°C (day/night temperature) on the high end of the plate and 5/5 oC on the cool end. Two temperature gradients ranging from 5 to 40°C were used. The first gradient, progressing from left to right on the thermogradient plate in dark, was alternated every 12 hours with the second progressing from front to back of the thermogradient plate with light. The study was repeated twice. Fifteen (15) seeds were used in each replication. The various temperature combinations had significant effect on final germination percentage, mean germination time, time for first germination and rate of germination. Alternating temperatures improved overall germination. The best germination at a constant temperature was at 20/20°C and 30/30°C. The best temperature regimes for seed germination at alternating temperatures were at 5/30°C, 10/30°C,15/30°C, 20/25°C, 20/35°C, 25/15°C, 25/20°C, 25/30°C, 30/20°C, 35/10°C, and 35/15°C.

Comparative germination ecology of the endemic Centranthus amazonum (Valerianaceae) and its widespread congener Centranthus ruber

Abstract Centranthus amazonum Fridl. & A. Raynal (Valerianaceae) is a critically endangered narrow endemic to Central–Eastern Sardinia (Italy), where it occurs in rocky habitats. In the present study, the germination ecology of this species was investigated and compared with the relatively widespread species Centranthus ruber (L.) DC. subsp. ruber. In particular, the effects of a range of constant temperatures (5–25°C) and two alternating temperature regimes (25/10 and 30/15°C) on seed germination were analyzed. For the two species, cardinal temperatures were determined as the reciprocal of time to 50% germination (t50). In addition, seed persistence in the soil was assessed by experimental seed burials. Seeds of both species were non‐dormant; however, C. amazonum produced more empty seeds and germination was slower and reached lower final percentages than C. ruber. Moreover, seed and seedling mass of C. ruber were higher than for C. amazonum and the lack of a persistent soil seed bank detected for C. amazonum increases vulnerability to extinction for this species. The present study provides new data on the germination ecology of the previously unstudied C. amazonum that may explain the rarity of this species when compared with the commonness of C. ruber.

Comparative Effects of Drought and Salt Stress on Germination and Seedling Growth of <i>Pennisetum divisum</i> (Gmel.) Henr.

Problem statement: Water stress due to drought and salinity is probably the most significant abiotic factor limiting plant and also crop growth and development. Salinity and drought stresses are physiologically related, because both induce osmotic stress and most of the metabolic responses of the affected plants are similar to some extent. Water deficit affects the germination of seed and the growth of seedlings negatively. Temperature is an exceedingly important factor in seed germination. It directly affects whether a plant can sprout and, if so, how long it will take to emerge from the ground. Approach: The objective of this investigation was to determine the effect of four alternating temperature regime, drought and salt stress on germination characteristics of Pennisetum divisum. Seeds were germinated at four alternating temperatures (10/20, 15/25, 20/35 and 25/40°C at 12 h light). Seeds were also germinated with the iso-osmotic concentrations of sodium chloride (NaCl) or in polyethylene glycol PEG8000 (0, -0.2, -0.4, -0.6 and -0.8 MPa) for 14 days. Concentrations were applied to determine their effects on seed germination and seedling growth under laboratory conditions. The effects of different osmotic concentrations of NaCl and PEG were compared to distilled water (control). Results: Optimum germination was attained at 15/25°C which corresponds to temperatures prevailing during spring time. The highest values of germination parameters were obtained with no osmotic potential (0 MPa) under 15/25°C. The final germination percentage and rate of germination in the Pennisetum divisum treated seeds were decreased with the increase of the osmotic potential. At treatment by PEG, the germination was severely decreased at -0.6 MPa. While, no germination occurred at- 0.8 MPa by NaCl. The results of the effects of the different osmotic potential of NaCl and PEG on the Radicle Length (RL) and the Hypocotyl Length (HL) mm of the tested P. divisum seeds were retarded when compared to the control. Conclusion: Results indicated germination sensitive to both the stresses. However, seedling growth was more sensitive to NaCl than was germination. However, seedling growth was more sensitive to NaCl than was germination responses to water stress induced by PEG and NaCl. Results also indicated that seed germination of P. divisum is less sensitive to osmotic potential indicating that the seeds of the species are efficient in osmotically adjusting to soluble salts. This suggests the possibility of revegtating moderately salt affected soils.

Morphological and physiological seed heterogeneity in the Mediterranean annual plant Tuberaria macrosepala (Cistaceae)

The morphometric features, germination requirements (under controlled conditions of light and temperature, and after different pre-sowing treatments) and cryopreservation tolerance of Tuberaria macrosepala (Cistaceae) seeds were studied. Constant (5, 10, 15, 20, 25, 30°C) and alternating temperature regimes (25/15°C, 30/20°C) with 16 h/8 h light/dark photoperiod and constant darkness conditions were used. Mechanical scarification, dry heat, boiling water, soaking in distilled water and soaking in gibberellic acid solution were used as pre-sowing treatments to enhance germination. Tuberaria macrosepala seeds were separated into three groups (light brown, medium brown and dark brown) according to the color of their seed coat. These three types of seeds also differed in size, weight and germinability. Dark brown seeds were found to be inferior to both medium and light brown seeds in size, final germination percentage and germination rate. No significant differences were found in seed weight between the three seed color types. Most seeds of the studied population were light brown. The final germination percentages of this type of seed ranged from 12 to 69%, depending on the temperature and light conditions used. Mechanical scarification significantly improved the final germination percentages of the three seed color types (86–96%). Therefore, seed coat impermeability to water (physical dormancy) appears to be the main cause of seed dormancy present in this species and seed color may be an indicator of hardseededness. Cryopreservation did not significantly decrease the final germination percentages. Therefore, cryopreservation could provide a method for long-term storage of germplasm of this species.

Effect of water stress by Polyethylene Glycol 8000 and Sodium Chloride on germination of Ephedra alata Decne seeds

Ephedra alata Decne is a perennial shrub and it is a very effective sand-binder. In Saudi Arabia, the species is associated with sand dunes formation, especially the mobile, non-saline and low moisture content ones. Its geographical distribution in Saudi Arabia includes the Northern, Eastern and Central regions. The aims of this study were to determine the effects of temperature, water potential and Sodium Chloride on germination of E. alata. Seeds were collected from King Khalid Centre of Wildlife Research and Development at Thumama (80 km north east of Riyadh), Saudi Arabia. Seeds were germinated at four alternating temperature regimes (8/22; 9/23; 13/27 and 18/35 °C). Seeds were also germinated under stress of aqueous Polyethylene Glycol (PEG) solutions mixed to create water potentials of 0; −0.3; −0.6; −1.2 and −1.5 MPa. Seed were also germinated in Sodium Chloride solutions of 0, 0.05, 0.1, 0.2 and 0.3 mol l −1. Optimum germination was attained at 13/28 °C that corresponds to temperatures prevailing during spring time. Seeds germinated in Polyethylene Glycol solutions exhibited significantly lower germination than control especially when water potential fell below −0.3 MPa. Germination was also negatively affected by 0.1 mol l −1 Sodium Chloride solution or above. Results indicated that the germination temperature responses of the nondormant seeds synchronize the event of germination with the season when environmental conditions are more favorable for subsequent growth and seedling establishment. Germination was also sensitive to both water potential and salinity.

Onset of Dormancy, Dormancy Levels, and Appropriate Seed Production Environment for Two Subspecies ofVernonia galamensis(Cass.) Less

Detailed germination studies were conducted on seeds of two subspecies of Vernonia. galamensis (nairobiensis and afromontana var. gibbosa), a potential industrial oil crop. Plants of both subspecies were grown at two experimental sites in Kenya and sequential harvesting carried out during seed development to determine the best production environment and optimum harvest time for low-dormant, high-quality seed-lots. Seeds harvested at different maturity levels were germinated under different temperature regimes before and after desiccation. The studies revealed that the onset of germinability and desiccation tolerance was achieved during the dry matter accumulation phase of seed development and that seeds developed dormancy 3 to 6 d after acquiring germinability, with high levels of germination only reaching under an alternating temperature regime. The seeds of the subsp. nairobiensis were shown to be more dormant than those of the subsp. afromontana var. gibbosa. Similarly, seeds harvested from a warmer en...

Effect of temperature on sporulation of Neozygites floridana isolates from different climates and their virulence against the tomato red spider mite, Tetranychus evansi

The fungal pathogen Neozygites floridana Weiser and Muma has been evaluated as a classical biological candidate for introduction into Africa against the invasive tomato red spider mite Tetranychus evansi Baker and Pritchard. In this study, the effect of temperature on sporulation, germination and virulence of three isolates of N. floridana collected from T. evansi in three climatically distinct regions of Brazil and Argentina was determined. Six constant temperatures of 13 °C, 17 °C, 21 °C, 25 °C, 29 °C and 33 °C were tested for their effect on the ability of the three fungal isolates to sporulate, germinate and kill the mites. Six alternating-temperature regimes of 17–13 °C, 21–13 °C, 29–13 °C, 33–13 °C, 33–23 °C, 33–28 °C under a 12 h photophase were also tested to estimate virulence of the three isolates against T. evansi. The Vipos isolate discharged more conidia than isolates from Recife or Piracicaba at all temperatures and sporulation was strongly temperature dependent. Optimal sporulation rates were observed at 25 °C while optimal germination rates were observed at 25 °C and 29 °C. At 29 °C, the shortest mean survival time of T. evansi (3.16 days, 95% CI of 3.05–3.27) was observed for the isolate from Vipos, while the longest LT 50 (3.47 days, 95% CI 3.34–3.59) was observed for the isolate from Piracicaba. Mortality of mites increased as the differences between alternating day and night temperatures increased from 8 °C (21–13 °C), to 10 °C (33–23 °C), to 16 °C (29–13 °C), with smallest and highest temperature differences of 4 °C (17–13 °C) and 20 °C (33–13 °C), both producing low mortalities. The overall results suggest that the Vipos isolate is better adapted to a wider range of temperatures than the other isolates tested.