Effect of temperature on germination,growth, and infectivity of the mosquito pathogen Tolypocladium cylindrosporum (deuteromycotina; hyphomycetes)

The mosquito pathogen Tolypocladium cylindrosporum was examined with regard to its response to temperature. Similar temperature ranges were found for growth, germination, and infectivity of blastospores and conidia. Germination occurred at 8° and 33°C but not at 6° and 35°C. Optimal germination and growth was noted between 24° and 27°C for both spore types. Infectivity of blastospores and conidia at different temperatures was examined by exposing L₂Aedes sierrensis larvae to concentrations of 5 × 10⁵ blastospores/ml or 5 × 10⁶ conidia/ml. Larvae were incubated at 12°, 15°, 25°, and 30°C. Infection occurred at all temperatures tested with LT₅₀ values ranging from 22.7 days (12°C) to 5.6 (25°C) days for conidia and 4.7 days (12°C) to 0.6 day (25°C) for blastospores. These results confirmed earlier findings that blastospores infected and killed host larvae more rapidly than conidia and suggested that this difference is largely due to the more rapid germination rate of blastospores. These experiments demonstrated that T. cylindrosporum can be active against mosquito larvae over a broad range of temperatures encompassing both the cold-water habitat of certain temperate mosquito species as well as the habitat of tropical vector species.     

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.     

Effect of relative humidity,temperature and fungicide on germination of conidia of Cercospora canescens caused the Cercospora leaf spot disease in mungbean

The aim of the present investigation was to determine the impact of relative humidity (RH) and temperature on conidial germination, nuclear position and effect of important fungicides on growth and conidial germination of Cercospora canescens. Germination of conidia was observed at RH range 92–100% at 5–35°C. Significant interaction between temperature and RH indicated that higher humidity and high temperature promoted quick germination both in the presence and absence of free moisture. Although in absence of free moisture at 92–95% RH higher temperatures 25–35°C promoted quick evaporation of moisture and no conidial germination. Number of germtube was increased significantly at the optimum temperature 25–30°C and higher humidity (98–100%). But higher temperature 25–35°C with lower RH did not support the conidial germination. This finding is very important for disease forecasting using meteorological data. The spray of Carbendazim as contact fungicide may not be useful since it is not effective against the conidia of C. canescens. Triadimefon did not inhibit the conidia germination but completely inhibited mycelium development at 50 μg/ml. Propriconazole inhibited both conidia germination and mycelial development. Therefore, Propiconazole may be taken as protective as well as curative spray. In non-systemic fungicide, Copper oxychloride gave anticipated result by inhibiting both conidial germination and mycelium development. Therefore, copper oxychloride can be used as protectant fungicides for Cercospora leaf spot caused by C. canescens.     

Secondary leaf fall of Hevea brasiliensis: factors affecting the production, germination and viability of spores of Colletotrichum gloeosporioides

The optimum temperature for growth and sporulation of Colletotrichum gloeosporioides from Hevea brasiliensis was between 26 and 32 ^oC, whereas spore germination exceeded 90% between 21.5 and 30.5 ^oC. Germination decreased in culture after 3 days, and on exposure of spores to sunlight or oven heat (46 ^oC) for 10 min. Spore viability and germination were sensitive to atmospheric humidity; at 99% r.h. germination was half that at 100% r.h. and was negligible below 97% r.h. Germination decreased by up to 30% after 3 h storage at 80% r.h. Continuous light favoured spore production in vitro, but spores produced in the dark had a higher percentage germination. No differences were detected between the numbers of spores germinating on leaves of different ages, although there were slightly more on susceptible cultivars and in the presence of extracts of uninfected susceptible leaves. Extracts from, infected leaves depressed spore germination, as did concentrations above 5 times 10⁵ spores/ml. The highest % germination was observed when naturally infected leaves were dry-stored for up to 20 days and then incubated for 2 days in a moist chamber.     

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.     

LIGHT REQUIREMENTS FOR MONOSPORE GERMINATION IN BANGIA ATROPURPUREA (RHODOPHYTA)1

Monospore germination, in Bangia atropurpurea (Roth) C. Ag. [= B. fuscopurpurea (Dillw.) Lyngb.] is light-dependent. In white light, the percent germination increases with increasing photon fluence rate until the response is saturated at 35 μmol · m^?2· s^?1. At a saturating photon fluence rate in an 18:6 h L:D cycle, 9 days are required for maximum germination. Green light is the most effective spectral region for monospore germination, although the process can occur in red and blue light if sufficiently high photon fluence rates are provided. Monospore germination and photosynthetic oxygen evolution are completely inhibited by DCMU at a concentration of 1 × 10^?6 M. Germination is reduced in a low CO₂ atmosphere and does not occur in the dark when glucose, maltose or inositol are supplied. It is concluded that photosynthesis is required for monospore germination.     

Cell cycle analysis in asynchronous cultures using the BUdR-Hoechst technique.

During synchronized germination of spores of Dictyostelium discoideum, protein synthesis begins almost concomitantly with syntheses of messenger-like RNA (mlRNA) and 4–5S RNA (presumably tRNA) in the swollen spore stage and the initiation of ribosomal RNA (rRNA) synthesis is somewhat delayed. DNA synthesis occurs in the early stages of the amoeba emergence phase. Cycloheximide (200 μg/ml) blocked spore germination as well as total protein synthesis, whereas actinomycin D (60 μg/ml) did not affect either. This concentration of actinomycin D selectively inhibited formation of rRNA but did not influence the synthesis of mlRNA. Examinations of RNA labeled with [¹⁴C]uracil during germination indicated that polysomes initially detectable in the course of the germination process contain ¹⁴C-labeled mlRNA. It was concluded that at least some of mRNA synthesized during germination of D. discoideum spores is involved in protein synthesis required for the germination.     

Effects of temperature and light on germination and early seedling development of the pine pink orchid (Bletia purpurea)

Orchid seed physiology is a poorly understood phenomenon owing to an emphasis on production and the challenges associated with propagating orchids from minute seed. We investigated the role of simulated south Florida temperatures and illumination (dark and 12 h photoperiod) in regulating germination and seedling development using asymbiotic seed germination assays of Bletia purpurea. Our objectives were to determine whether in situ germination is limited by seasonal temperatures and to determine whether temperature alters responses to illumination. Bletia purpurea seeds were able to germinate to > 90% under all treatments. The greatest germination after 3 weeks was observed at 29/19°C under continual darkness and at 25°C under dark and illuminated conditions. The slowest germination was observed at simulated winter temperatures (22/11°C). Illumination initially inhibited germination and development, but resulted in equal or greater development by week six. Germination under 22/11°C was strongly inhibited by illumination, indicating an interaction between temperature and light sensing systems.     

Control by imazalil of fruit storage rots caused by Alternaria alternata

The fungicide imazalil has potential value for controlling post-harvest diseases caused by Alternaria alternata in pears, apples and persimmons. Imazalil was active in vitro on germination and hyphal growth (ED₅₀) at 1.4 and 0.5 μg/ml, respectively. Protectant action of the fungicide lasted only 1 day after treatment. At 1000 μg/ml the fungicide inhibited development of Alternaria rot in inoculated apples at 0 °C and in naturally infected pears and persimmons at–1 °C.     

Dracaena Leaf Proliferosis, a Newly Recorded Disease Affecting Dracaena sanderiana in Egypt

Dracaena leaf proliferosis is a newly reported disease affecting Dracaena sanderiana in Egypt. A cause and effect relationship between this disease and the fungus,Fusarium proliferatum var. minus has been established. In addition to D. sanderiana the fungus was found to be pathogenic, when tested in the laboratory, to several other members of the family Liliaceae. While the in vitro growth of the fungus is optimum at 25 °C, symptom expression is best at 30°C. Twelve fungicides were tested for their in vitro effect on fungal growth. Benlate, Rubigan, Saprol, Cercobin and Vitavax-200 came first on the list and inhibited growth at 2.5, 12.0, 55.0, 75.0, and 94.0 μg/ml, respectively. Although, Benlate was the most effective fungicide in this respect it failed to demonstrate similar effect on disease development when applied to plants artificially inoculated with the fungus. Fungal growth was completely inhibited on PDA medium by a bacterium belonging to Bacillus sp. but when the bacterium at a concentration of 1 × 10¹¹ cell/ml was applied 24 h before, at the same time with, or 24 h after inoculation no control of the disease was achieved. Naturally-infected plants could, however, be freed from infection when subjected to a hot air treatment at 35 ± 5 °C during day time and 25 ± 5° C at night for 3 months.     

Spore germination inCylindrospermum sp.: Influence of gases and growth conditions

Influence of different gases on spore germination ofCylindrospermum sp. revealed that acetylene and ethylene suppressed the germination which was more pronounced at their higher concentrations. Germination was completely inhibited under the atmosphere of hydrogen and argon even when supplied with 1% CO₂. Carbon dioxide, both in air and in N₂, stimulated the process. However, higher concentrations of CO₂ inhibited the germination in a concentration-dependent manner, possibly due to a decrease in pH. Germination was completely arrested in the absence of light and nutrients. The energetic requirement for germination was not efficiently fulfilled by photosystem I (PS II was blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea) or under conditions of anoxygenic photosynthesis (medium supplemented with sodium sulfide).     

Factors influencing spore germination,appressoria formation and disease development inCamellia sinensis byGlomerella cingulata

Factors associated with conidial germination and appressoria formation ofGlomerella cingulata causing the brown blight disease of tea (Camellia sinensis) were studiedin vitro. Spore germination and appressoria formation were optimum at a temperature of 25°C, pH 5.0, 7 h light/day regime and a 24-h incubation period. At a concentration of conidia of 1200/μL 10-d-old culture,G. cingulata exhibited a maximum germination and appressoria formation. A maximum production of lesions was also evident on detached tea leaves at this spore concentration and in diffuse light. Diffusates of a phenolie nature collected from tea varieties susceptible and resistant toG. cingulata inhibited spore germination and appressoria formation. Diffusates from resistant varieties were more fungitoxic than those from susceptible varieties. Some phenolics known to be present in tea leaves, when testedin vitro, exhibited varying degrees of fungitoxicity. Pyrogallol totally inhibited spore germination, while pyrocatechol and phloroglucinol completely inhibited appressoria formation.     

Characterisation of Isaria fumosorosea isolates and their virulence toward the Diamondback Moth,Plutella xylostella

Some morphological and physiological characteristics of an Isaria fumosorosea isolate with diminished virulence, IFCF01-D, and its parent isolate, IFCF01, were evaluated and laboratory bioassays were performed to assess their virulence against Plutella xylostella. The relationship among these traits and virulence against P. xylostella is discussed. There were no significant differences in conidial viability, spore production and the time required for 50% germination (GT₅₀). Spore viability after incubation for 24 h at 25°C was greater than 98% for both isolates tested. Spore production on potato dextrose agar after 14 days incubation at 25°C was 4.68 × 10⁸ and 4.59 × 10⁸ conidia/mL for IFCF01 and IFCF01-D, respectively. When exposed to high temperatures (40, 45, 50 or 55°C) through a water bath for 10 min, conidial germination ranged from 0.83% to 84.0% for IFCF01 and 0% to 86% for IFCF01-D. Germination rate showed a negative relationship with the exposure temperature for both isolates. The per cent germination of isolate IFCF01 24 h after ultraviolet (UV) radiation (18 W, 240–260 nm) varied from 0% to 92% and 0% to 81% for IFCF01-D. Germination rate and the exposure time exhibited a negative correlation for both isolates tested. Conidial surface hydrophobicity of IFCF01 (60%) was significantly higher than that of isolate IFCF01-D (53%). Subsequently, using the cicada exuviae as the substrate for enzymatic analysis, Pr1 and chitinase activity demonstrated the contrasting virulence traits: higher specific activities for the more virulent IFCF01 and lower enzymatic levels for isolate IFCF01-D.     

Antifungal compounds from Bacillus subtilis B-FS06 inhibiting the growth of Aspergillus flavus

The cell-free culture filtrate (CCF) was prepared from a culture of an Aspergillus flavus antagonist, Bacillus subtilis B-FS06. The CCF inhibited the growth and spore germination of A. flavus at a series of concentrations (10, 25, 50%) (v/v). It still retained the activity after treatment at pH values ranging from 2 to 12 for 24 h or at 100 °C for 30 min. The antifungal activity, however, was reduced by 30% after treatment at 121 °C for 20 min. After purification by anion exchange chromatography, gel filtration chromatography and HPLC, the active compounds revealed six ion peaks: [M–H] m/z = 1006.78, 1020.71, 1034.74, 1049.54, 1056.78, and 1071.64 by using electrospray ionization mass spectrometry (ESI-MS) analysis. In the presence of the active compounds at 200 μg/g, the growth of A. flavus on peanuts was completely inhibited. Ting Zhang and Zhi-Qi Shi contributed equally to this work.     

Effects of temperature and water potential on the germination of muskmelon cultivars

The rate and final germination of four muskmelon cultivars (Cucumis melo) were examined in response to incubation temperatures of 20, 26 and 32°C. Germination was also characterised at 26°C pr 32°C over a range of water potentials from 0 to - 1000 kPa achieved with solutions of polyethylene glycol. The germination of one cultivar, TAM-Uvalde, was consistently slower at 20°C than at 26°C or 32°C. The other three cultivars, Perlita, TAM-Dew and Greenflesh, were inhibited by incubation at 32°C. However, the germination responses of cvs Perlita, TAM-Dew and Greenflesh at 26°C or 32°C improved as water potentials were reduced from 0 to – 200 or – 400 kPa. Cv. TAM-Uvalde was extremely sensitive to water stress and failed to germinate at water potentials below – 600 kPa when incubated at 26°C. The inhibition of germination at low water potentials was partially reversed in all cultivars by increasing the incubation temperature from 26°C to 32°C. It is suggested that the inhibition of germination at 0 kPa (distilled water) was due to a seed coat-mediated barrier to oxygen that could be reversed by removal of the seed coat or exposure to an oxygen-enriched atmosphere.     

Effect of insulin on glucose oxidation and amino isobutyric acid transport and binding of insulin in chicken thymocytes

In chicken thymocytes isolated from 15–40 day-old chickens, after a 2 h incubation at 37°C, insulin stimulated amino isobutyric acid uptake (maximal response: 40–50% of increase at 1 μg insulin/ml and half maximal response at 60 ng/ml) by specifically stimulating the influx without altering the efflux. Insulin also stimulated glucose oxidation (maximal response: 11% of increase at 1 μg insulin/ml). Binding of ¹²⁵I-labelled chicken insulin to thymocytes was rapid and higher at 15°C than at 37°C. At steady state, (90 min at 15°C), chicken, porcine and goose insulins were equipotent in inhibiting the binding of ¹²⁵I-labelled chicken insulin. Maximal binding capacity was estimated at 1250 pg insulin/10⁸ cells, i.e., 1250 binding sites/cell with an apparent dissociation constant of 200 ng insulin/ml at 15°C. Degradation of ¹²⁵I-labelled chicken insulin in the incubation medium was negligible at 15°C but very noticeable at 37°C. Therefore, the low level of insulin binding at 15°C reflects a true scarcity of insulin receptors in chicken thymocytes as compared to rat thymocytes.     

Physiology and fine structure of sporangiospore germination in Piptocephalis unispora prior to infection

Germination of the sporangiospore of Piptocephalis unispora Benjamin, observed by means of light and electron microscopy, involved the formation of a new inner wall which became continous with the inner layer of the wall of the germ tube. The outer wall layer of the germ tube was continous with the original inner wall layer of the dormant spore. Preliminary details of appressorium structure were noted. Nutritional experiments indicated that sporangiospores required external sources of utilisable nitrogen and carbon compounds for maximal swelling and germ tube production. Limited development occurred when either nutrient was supplied singly. Comparison of germination of the asexual spore with that in other Mucorales, especially the Kickxellaceae, has been made, and the merosporangial status in P. unispora discussed.Non-Standard Abbreviations CH casein hydrolysate - Q spore quotient     

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.     

Laboratory studies on the fungus Verticillium lecanii, a larval pathogen of the large elm bark beetle (Scolytus scolytus)

From 1972 to 1974, estimates of the natural larval mortality (> second instar) of elm bark beetles caused by pathogenic organisms were always below 7'5 % of the beetle population. The pathogenic fungus Verticillium lecanii was frequently isolated from field-collected dead larvae, and in the laboratory all larvae were killed in 5 days when exposed to spore concentrations of 4·5 × 10⁶ spores/ml. V. lecanii begins to lose its pathogenicity after prolonged culture on artificial media. The time taken for V. lecanii to kill Scolytus scolytus larvae when exposed to a logarithmic series of spore dilutions from 9·1 × 10⁷/ml to 9·1 × 10³/ml increased with decreasing amounts of inoculum. Even at spore concentrations as low as 9·1 × 10³/ml the mortality of treated larvae was greater than that of untreated individuals. At 100% r.h. all treated larvae were killed over a temperature range of 5–30 °C; those maintained at 25 °C were killed most rapidly and those kept at 5 °C the slowest.     

In vitro and In vivo Effects of Some Fungicides against the Chickpea Blight Pathogen, Ascochyta rabiei

The effects of various fungicides on mycelial growth and spore germination of Ascochyta rabiei were determined by incorporating them into potato dextrose agar and measuring colony diameter and observing colony growth and spore germination at 20 ± 2°C. Eight fungicides prevented spore germination of the pathogen at concentrations of 0.125–2 μg/ml, three hindered mycelial growth at 2–4 μg/ml and seven failed to inhibit mycelial growth even at 128 μg/ml. The reference fungicide for the pathogen, chlorothalonil, stopped conidial germination at low rates but did not prevent mycelial growth at 128 μg/ml. Thirteen fungicides were tested against seed infections of the pathogen, and benomyl + thiram, carbendazim and carbendazim + chlorothalonil seed treatments gave more than 85% inhibition on both vacuum‐infiltrated and naturally infected seeds. Coating the seeds with polymers did not increase the effectiveness of fungicides. Three fungicides; (azoxystrobin, chlorothalonil and mancozeb), gave the highest protection in the field but protection decreased with increased inoculum pressure. Addition of humic acid to fungicide suspensions did not affect their performance.