Teliospore Germination of Soybean Rust Fungus (Phakopsora pachyrhizi Syd.)

Teliospores of the soybean rust fungus (Phakopsora pachyrhizi Syd.) germinated after treatment with 10—12 wetting and drying cycles at room temperature. Spores swelled, vacuolated and germinated with a slightly curved basidium bearing 1—4 sterigmata with basidiospores. High germination rates were observed when telia were stored at 5 °C for 5—6 months before breaking dormancy.     

Sterile Germination Requirements of Seeds of Some Water Plants

A sterile germination study with seeds of some common phanerogamic water plants showed almost 100 per cent germination for seeds of Alisma plantago–aquatica, Baldellia ranunculoides and Nymphaea alba. Seeds of Potamogeton lucens could be germinated to about 40 per cent, seeds of Polygonum amphibium germinated sporadically while those of Cladium mariscus could not be germinated at all. Freshly harvested seeds of Alisma and Baldellia showed an ability to germinate at both 20°C and 35°C. A stratification period of one month at +4°C gave germination of all species tested, with the exception of Cladium. Potamogeton germinated in light only, the other species both in light and darkness. Treatment times for surface sterilization in disinfectants are given.     

Germination and Survival of Fusarium graminearum Macroconidia as Affected by Environmental Factors

The effects of temperature (4–20°C), relative humidity (RH, 0–100%), pH (3–7), availability of nutrients (0–5 g/l sucrose) and artificial light (0–494 μmol/m²/s) on macroconidial germination of Fusarium graminearum were studied. Germ tubes emerged between 2 and 6 h after inoculation at 100% RH and 20°C. Incubation in light (205 ± 14 μmol/m/s) retarded the germination for approximately 0.5 h in comparison with incubation in darkness. The times required for 50% of the macroconidia to germinate were 3.5 h at 20°C, 5.4 h at 14°C and 26.3 h at 4°C. No germination was observed after an incubation period of 18 h at 20°C in darkness at RH less than 80%. At RH greater than 80%, germination increased with humidity. Germination was observed when macroconidia were incubated in glucose (5 g/l) or sucrose (concentration range from 2.5 × 10^?4 to 5 g/l) whereas no germination was observed when macroconidia were incubated in sterile deionized water up to 22 h. Macroconidia germinated quantitatively within 18 h at pH 3–7. Repeated freezing (?15°C) and thawing (20°C) water agar plates with either germinated or non‐germinated macroconidia for up to five times did not prevent fungal growth after thawing. However, the fungal growth rate of mycelium was negatively related to the number of freezing events the non‐germinated macroconidia experienced. The fungal growth rate of mycelium was not significantly affected by the number of freezing events the germinated spores experienced. Incubation of macroconidia at low humidity (0–53% RH) suppressed germination and decreased the viability of the spores.     

Some factors influencing spore germination and penetration of Alternaria longipes

The ranges over which the germination of conidia of Alternaria longipes was > 50% were 10–35 °C on agar and 15–30 °C on tobacco leaf disks. Germination was optimal at 22.5 °C; so was germ-tube growth, reaching c. 300 and 102 μm on agar and leaf disks respectively after 12 h. On average, 27% more conidia germinated and germ-tubes were 62% longer on disks from leaves washed for 5 min under running water than on disks from unwashed leaves. At controlled saturation deficits germination after 8 h at 1.1 and 2.3 mb was 42.3 and 9.3% respectively and the rate of germ-tube growth was < 0.8 μm/h, compared with 94.4% and 8.3 μm/h in standing water. These results, together with some field data, suggests that germination in the field is largely restricted to periods when free moisture is present on leaves. In Malawi, leaf temperatures and the duration of dew at night were adequate to allow germination and penetration in the absence of rain. Pollen, when applied with the inoculum, had little effect on the number of germinated conidia, but caused a c. tenfold increase in the number of successful penetrations.     

Agarose Medium for Germination of Oospores of Phytophthora cactorum

When oospores of Phytophthora caetorum from 30-day-old culture were treated with 0.25% KMnO₄ for 20 min and incubated at 24°C under light for 10 days, 65–75% germinated on water agar and water agarose but only 1–21% germinated on V-8 agar and S+L agar. Water agarose was selected because germinated oospores formed restrieted colonies on this medium that could be isolated easily. KMnO₄ treatment killed sporangia, chlamydospores and mycelial fragments present in oospore suspensions. Under the above conditions, approximately 44% of oospores from 10-day-old culture germinated and the optimum germination rate of about 75% was obtained when oospores reached about 20 days old.     

Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape)

Ascospores of both A‐group and B‐group Leptosphaeria maculans germinated at temperatures from 5–20°C on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A‐group ascospores had germinated at 10–20°C and some B‐group ascospores had germinated at 5–20°C. The percentages of both A‐group and B‐group ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5–20°C. The observed time (Vo₅₀) which elapsed from inoculation until 50% of the spores had germinated was shorter for B‐group than for A‐group ascospores. Germ tube length increased with increasing temperature from 5–20°C for both ascospore groups. Germ tubes from B‐group ascospores were longer than germ tubes from A‐group ascospores at all temperatures tested, but the mean diameter of germ tubes from A‐group ascospores (1.8 μm) was greater than that of those from B‐group ascospores (1.2μm) at 15°C and 20°C. The average number of germ tubes produced from A‐group ascospores (3.8) was greater than that from B‐group ascospores (3.1) after 24 h of incubation at 20°C, on both water agar and leaf surfaces. Germ tubes originated predominantly from interstitial cells or terminal cells of A‐group or B‐group ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A‐group ascospores grew tortuously with extensive branching, whilst those from B‐group ascospores were predominantly long and straight with little branching, whether the ascospores were produced from oilseed rape debris or from crosses between single ascospore isolates, and whether ascospores were germinating on water agar or leaf surfaces.     

Germination of the conidia of Peziza ostracoderma

Conidia ofPeziza ostracoderma Korf, washed by centrifugation and decantation, germinated in a high percentage in glass-distilled water and various nutrient solutions. They also germinated on a wide variety of agar media and in citratephosphate buffers from pH 3 through 8. The conidia first swell to twice their original size, and then emit one cylindrical germ tube. The cardinal temperatures for germination were: minimum, below 3° C; optimum, 20°–33° C; maximum, between 38° and 42° C. A liquid film of water was required for germination.     

The effect of Sea Water and Temperature on the Germination Behaviour of Crithmum maritimum

The seeds of Crithmmm maritimum L. were germinated floating on various concentrations of sea water up to 50% at constant temperatures of 5, 10, 15, 20, and 25°C and at alternating temperatures of 5 and 15°C. 5 and 25°C. and 15 and 25°C. Significantly higher germination was obtained at alternating than at constant temperature. When two constant temperatures at which no germination occurred were alternated, good germination was obtained. There was reduced germination and increase in time of first germination as sea water concentration increased, in the absence of sea water, high temperature caused not only severe inhibition of germination but also permanent injury to the seeds. The results help to explain the germination behaviour of the species in nature.     

Effect of salinity,temperature and hypersaline conditions on the seed germination in Limonium mansanetianum an endemic and threatened Mediterranean species

Abstract

Limonium mansanetianum is catalogued as critically threatened (CR) species and it is included in Valencian Catalogue of Threatened Plant Species. Limonium mansanetianum is a gypsicolous species, which only lives in a restricted area to south-centre of Valencia province (Spain). The species is a low-branched woody shrub with summer flowering. The influence of incubation temperature (10°, 15°, 20° and 25°/20?°C) and salinity (0%–3.0% NaCl) on seed germination of L. mansanetianum was studied. Best seed germination was obtained in distilled water controls. Seed germination decreased with an increase in salinity and few seeds germinated at 2.5% and 3.0% NaCl. Optimal temperature regime for germination was 15?°C where germination in 0.5% and 1.0% NaCl was not affected. Recovery and hypersaline conditions experiments showed that L. mansanetianum seeds displayed a greater tolerance to high salinity and temperature stress before germination.     

Epidemiology of Cladosporium allii and Cladosporium allii-cepae, leaf blotch pathogens of leek and onion.

Conidia of Cladosporium allii and C. allii-cepae germinated over the temperature range 2–30°C on agar with optimal responses at 15–20°C (C. allii) and 20°C (C. allii-cepae). Conidia of both fungi germinated in water and at c. 100% relative humidity (r.h.) but not at lower humidities on leaf and glass slide surfaces. Germination was more rapid when spores were applied dry to agar or leaves than when applied in water or nutrient solution. More lesions developed when conidia of C. allii-cepae were deposited dry on onion leaf discs or leaf surfaces than when they were applied suspended in water. Conidia of both fungi required 18–20 h at c. 100% r.h. to germinate and infect when applied dry to leaves. Damaging the leaves or the addition of nutrients to the leaf surface increased the incidence of infection by C. allii-cepae compared to controls. Inoculated onion bait plants placed out-of-doors developed infection after at least 17 h at c. 100% r.h. or with leaf wetness. Similar conditions were necessary for infection of bait plants exposed in onion and leek crops infected by C. allii-cepae and C. allii respectively. Disease development and spread of infection occurred at different rates over the same period in two different cultivars of leeks, with spore concentrations increasing in proportion to disease. Spore numbers in the air fell considerably when infected leeks were ploughed under.     

Seed germination of the weed Rumex obtusifolius after on-farm conventional, biodynamic and vermicomposting of cattle manure

This study investigated whether composting methods differ in their impact on seed germination of Rumex obtusifolius (broad‐leaved dock). Weed seeds were buried in windrows of cattle farmyard manure, removed at monthly intervals and germinated during the course of 7 months. Composting methods differed in the maximum temperatures reached (63°C for conventional and biodynamic composting and 35°C for vermicomposting), the addition of 1000 m^?2 earthworms (Eisenia fetida) for vermicomposting and the inoculation of biodynamic preparations for biodynamic composting. After 1 month in windrows, germination rate of Rumex seeds was significantly higher in vermicompost (48%) than in conventional (28%) or biodynamic compost (18%). After 2 months in windrows, 26% of the seeds germinated in vermicomposting windrows, while those inserted in conventional and biodynamic windrows showed a negligible germination (0% and 2%, respectively). After 3 and 4 months, only seeds under vermicomposting germinated (22% and 3%, respectively). No germination was determined when seeds were inserted for longer than 4 months in any of the treatments. Seeds stored at room temperature germinated at 89% over the course of the experiment. Results suggest that the maximum temperature reached in windrows is not the single main factor reducing weed seed germination during composting.     

Rhythmic Behavior in Germination of Cocklebur Seeds

Non-dormant, lower seeds of cocklebur (Xanthium pensylvanicum Wallr.) germinated with unimodal flush after 20 and 36 h from the start of water imbibition at 33 and 23°C, respectively. At 28°C, however, germination occurred bimodally, the time of each peak coinciding with that at 23 and 33°C. This type of germination behavior was induced even at 33°C, when the seeds were contacted with some osmotica. Further, the application of different osmotica at 28°C caused a rhythmic multimodal germination with a period of about 16 h. It was suggested that an endogenous rhythmicity may be involved in the control of cocklebur seed germination.     

Adaptation to habitat in Aquilegia species endemic to Sardinia (Italy): Seed dispersal,germination and persistence in the soil

Abstract

The autecology of the Sardinian endemics Aquilegia barbaricina Arrigoni et Nardi and A. nugorensis Arrigoni et Nardi were investigated. Peaks of anthesis and seed dispersal were recorded for five populations occurring in two distinct habitats, one riparian and one rupicolous. Germination tests were carried out on seed lots belonging to each population by sowing seeds at 10, 15, 20, 25 and 25/15°C. In addition, seeds were incubated for 2 months at either 25°C (summer), 5°C (winter) or 25°C for 2 months plus 2 months at 5°C (summer followed by winter–SW), and then moved to the germination temperatures. Embryo measurements were taken during pre-treatments and germination. Experimental seed burials were carried out for two populations of each species. Both species dispersed in summer. The population of A. nugorensis occurring on rocky outcrops differed in phenology from both the other A. nugorensis population from riparian vegetation and from A. barbaricina. Both species showed morphophysiological seed dormancy, with <50% germination under laboratory conditions. All riparian populations germinated only after the SW pre-treatment, while the rupicolous population germinated at 25°C, without any pre-treatment. Low germination percentages were observed in the experimental seed burials, suggesting the ability for both species to form a persistent soil seed bank.     

Effects of light, temperature and water stress on germination of Artemisia sphaerocephala

Artemisia sphaerocephala is widely used for vegetation rehabilitation, but its germination is very low after air seeding of achenes. We explored effects of light, temperature and water stress on germination. Results show that both final percent germination and germination rate were increased by temperature increment, with the highest values occurring at 15: 25°C (night: day) in dark and 20: 30°C under light. Light inhibited germination, especially at lower alternating temperatures (5: 15°C and 10: 20°C). The alternating temperature window for germination was slightly narrower under light than in dark, and germination was slower under light than in dark across the temperature range. Achenes incubated in the dark and at constant temperatures had over 80% germination at 10 to 25°C, with an optimum at 20°C. Under dark and 25μmol m^‐2 s^‐1 light flux density at 10: 20°C, final percent germination was over 94%, but if the light flux density was increased to 100 and 400 μmol m^‐2 s^‐1, final percent germination was significantly lower (64% and 38% respectively). However, achenes could keep their germination capacity for a long time (over 50 days) and germinate well after going back to the dark. Germination was also lower under water stress and few achenes germinated at ‐1.4 MPa. This was more pronounced at high and low temperatures. Given these findings and the prevailing climatic characteristics, the most suitable time for air seeding of achenes may be mid‐May.     

Effects of pH,NH<Subscript>4</Subscript>-N concentration,temperature, and storage period on basidiospore germination in an ectomycorrhizal ammonia fungus <Emphasis Type="Italic">Hebeloma vinosophyllum</Emphasis>

Basidiospore germination in an ectomycorrhizal ammonia fungus Hebeloma vinosophyllum was stimulated by 10–500 mM NH₄Cl aqueous solution at pH 4.5–9.0, but not by pure water. The basidiospores germinated at 10°–35°C with an optimum at 25°–30°C. The highest germination percentage (83.0%) was observed in 100 mM NH₄Cl aqueous solution adjusted to pH 8.0 by KOH, when the basidiospores were incubated at a density of 10⁶ spores/ml at 30°C for 14 days. The percent germination value decreased with the increased duration of storage under both dry and wet conditions. Humidity and temperature affected the longevity of H. vinosophyllum basidiospores. The basidiospores maintained their germination ability longer under a dry condition than under a wet condition. The greatest longevity was accomplished by storage at 15°C under a dry condition.     

Germination Response Patterns during Dormancy Loss in Achenes of Six Perennial Asteraceae from Texas, USA

Abstract When subjected to simulated habitat temperatures, achenes of six perennial Asteraceae from southcentral Texas came out of dormancy during summer. In the early stages of dormancy loss, achenes of Erigeron modestus, Gaillardia suavis and Hymenoxys scaposa germinated (to ≥ 10%) in light at 12/12 hr daily thermoperiods of 15/6, 20/10 and 25/15°C and those of Pinaropappus roseus at 15/6 and 20/10°C. After additional dormancy loss, achenes of these four species also germinated at 30/15 and 35/20°C. Achenes of these four species had a Type 1 germination response pattern, which heretofore has not been reported in perennial Asteraceae. Achenes of Chaptalia nutans first germinated (to ≥ 10%) at 20/10 and 25/15°C and those of Hymenopappus scabiosaeus at 20/10°C, but with further loss of dormancy achenes of both species also germinated at 15/6, 30/15 and 35/20°C. Thus, achenes of these two species had a Type 3 pattern. This is the first report of perennials in any family with a Type 3 response pattern whose seeds come out of dormancy during summer. Presence of annual and perennial Asteraceae with Type 2 in temperate eastern North America and annual and perennial Asteraceae with Type 1 in southcentral Texas causes us to conclude that climate is more important than the type of life cycle in determining the type of germination response pattern.     

Effects of drought stress on seed germination of ornamental sunflowers

The response to drought stress on germination was investigated on three hybrids of ornamental sunflower, ‘Hadar’, ‘Pazit’, and ‘Zohar’. Different levels of water potential [Ψ: 0.0 (control), ?0.15, ?0.30, ?0.45, ?0.60, ?0.75, and ?0.90 MPa] were adopted using polyethylene glycol-6000 (PEG6000) at four germination temperatures (15, 20, 25, and 30 °C). Final germination percentage, mean germination time, germination index, germination rate index, and germination stress tolerance index were used to evaluate the genotype response to PEG-induced water stress. Shoot and root length and fresh and dry weight were measured on seeds germinated at 20 °C under the different levels of water potentials. During germination, the three ornamental sunflowers showed to be more sensitive to suboptimal temperature than to supraoptimal. Decreasing water potential of imbibition solution progressively inhibited and delayed seed germination. Among cultivars, ‘Hadar’ and ‘Pazit’ performed better at temperature lower than 30 °C. ‘Zohar’ showed a lower sensitivity to PEG-induced water stress at all temperature conditions. Water stress during seed germination depressed the following seedling growth under favourable conditions. As a result, shoot and root length and fresh and dry weight was significantly lower in seedlings from seed germinated at ψ ≤ 0.45 MPa.     

Prosopis chilensis is a plant highly tolerant to heat shock

At temperatures between 25 and 35°C, 100% of Prosopis chilensis seeds germinated within 24 h. At higher temperatures, the germination rate was reduced; at 50°C, seeds did not germinate. After germination at 25°C, the optimal temperature for seedling growth was 35°C and the seedlings did not grow at a temperature of 50°C. However, when germination was at 35°C, the optimal temperature for seedling growth was 40°C and some seedlings grew at 50°C, suggesting that thermotolerance was induced during seed germination at 35°C. Further thermotolerance can be induced in seedlings germinated at 35°C, by exposing them to 40°C for 2h. Under these conditions, seedlings exhibited increased growth rate at 45 and 50°C. Fluorography of SDS-polyacrylamide gel electrophoresis of the proteins synthesized and accumulated during 2 h at temperatures of 35, 40, 45 and 50°C in the presence of [³⁵S]methionine revealed the expression of 11 proteins not detectable at 35°C. Most of the proteins present at 35°C also increased in expression. The temperature for maximal expression of these proteins was 45°C.     

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

Environmental factors influencing the infection of wheat by Puccinia graminis

Germination rate and total germination of Puccinia graminis uredospores were directly related to pustule age and duration between spore collections. Partial drying of the spores enhanced germination rate; keeping them for 18 h at 100% r.h. reduced both rate and total germination. Spores germinated in polystyrene dishes between 4 and 29 °C and optimally between 15 and 23 °C Light (3 cal/cm²/h) had little effect on germination on moist surfaces but inhibited germination on the leaf. In Hybrid 229/8 wheat this effect was more pronounced than in var. Little Club. The number of primary infections increased linearly with duration of surface wetness with a narrow temperature optimum at 23.5 °C. Two phases of infection could be distinguished: germination (requiring darkness and capable of taking place over a wide temperature range) and penetration (requiring light and slightly higher temperature than for germination). Stomatal closure caused by subjecting the plants to water stress led to proporational reductions in infection. The results are discussed in relation to dew formation.