Percentage Of Germinated Conidia Research Articles

Role of pycnidia in twig and blossom blight and stem dieback of highbush blueberry caused by Phomopsis vaccinii in British Columbia

Twig and blossom blight, and stem dieback, has become an impediment to highbush blueberry (Vaccinium corymbosum L.) production in British Columbia. Periodic assessment of disease symptoms and pathogenicity test confirmed Phomopsis vaccinii to be the major causal agent of the disease. Symptomatic tissues sampled at 7- to 10-day intervals in the 2014 and 2015 growing seasons were examined for presence of pycnidia, their developmental stages, and conidial presence in relation to phenological status of blueberry. Based on histological analysis, pycnidia were grouped into a series of developmental stages, referred to as pre-conidial, early-conidial, conidial, conidial-release and post-conidial stages. These different stages of development coincided with the phenological stages of blueberry plants during the growing season. Pycnidia at the conidial and conidial-release stages were predominantly found on symptomatic tissues sampled from bud-break to bloom; these pycnidia had high conidial contents of 1.0–2.0 × 104 conidia pycnidium−1. Pycnidia at the post-conidial stage were mostly found on symptomatic tissues sampled from green-fruit to post-harvest, under warm and dry weather conditions. Pycnidia at the pre-conidial stage were predominantly observed on symptomatic tissues sampled during latter parts of the growing season, from bud-set to leaf-fall. Mycelial growth of P. vaccinii isolates on potato dextrose agar was measured in response to temperatures from 4 to 32°C; the optimum growth occurred between 20 and 28°C. The number of pycnidia produced on quarter-strength potato dextrose agar at different incubation conditions varied amongst P. vaccinii isolates, and the optimum production was recorded at 16°C with a photoperiod of 14 h light/10 h dark or 14 h UV-A/10 h. Percentage germination of conidia of P. vaccinii isolate 11 BB 14 on water agar was higher at 16, 20 or 24°C than at 8 or 12°C. Conidia at 16°C reached 50% germination at ≥56 h incubation, whereas conidia at 20 and 24°C reached 50% germination at ≥72 h. Percentage germination of conidia at 8 and 12°C remained <50% during 104 h incubation. These findings provide an improved understanding of the role of pycnidia in the epidemiology of twig and blossom blight and stem dieback caused by P. vaccinii on highbush blueberry.

The mechanism of the mycoinsecticide diluent on the efficacy of the oil formulation of insecticidal fungus

Adverse conditions, including low humidity, UV irradiation, and high temperature, appreciably affect the efficacy of mycoinsecticides. Oil formulation increased the virulence of Metarhiziumanisopliae var. acridum (Ascomycota: Hypocreales) against locusts and grasshoppers by reducing the dependence on saturated water. A mycoinsecticide diluent (a water-in-oil emulsion) has been widely used to dilute the oil formulation of M. anisopliae in China. The aim of our study was to elucidate the mechanism by which the mycoinsecticide diluent improves the virulence of M.anisopliae. We investigated the effects of the mycoinsecticide diluent on the virulence, invasion speed, and viability of the conidia under various adverse conditions. The results demonstrated that the mycoinsecticide diluent significantly improved the virulence of conidia at low humidity (68, 75, and 84%). In particular, at an RH of 68%, the LT50 for locusts treated with the emulsion was 5.4 days and was 31.6% lower than the value for locusts treated with an oil formulation. In addition, the concentration of the hyphal bodies found in the haemolymph of locusts treated with emulsion was about 27-fold higher than that in locusts treated with oil formulation four days after inoculation. This result was further confirmed by determining the concentration of M. anisopliae var. acridum DNA in locust haemolymph using quantitative PCR. The percentage germination of conidia in the emulsion was also significantly higher than that in oil at 68% RH. There was no significant difference in percentage germination between conidia treated with the emulsion and oil when exposed to irradiation with ultraviolet-B (UV-B) or high temperature. These results demonstrate that the mycoinsecticide diluent enhances the virulence of M.anisopliae formulated in oil at low humidity by providing adequate water for germination without interfering with the UV tolerance and thermotolerance of the conidia.

Mass Production of the Insect-Pathogenic Fungus, Metarhizium anisopliae (Metchnikoff) Sorokin (Deuteromycota: Hyphomycetes), on Different Cereal Grains.

Five cereal grains. namely. maize (Zea mays L.). rice (Oryza sativum L.). sorghum (Sorghum bicolar (L.) Moench). millet (Pennisetum glaucum (L.) R. Br), and wheat (Triticum aestivum L.) were crushed and evaluated for their potentials to support growth and sporulation of the insect-pathogenic fungus. Metarhizium anisopliae (Metchnikoff) Sorokin (isolates V275 and ARSEF 3297). The conidia produced were tested for viability and virulence against Galleria mellonella Met. and Tenebrio molitor L using immersion bioassay and spore bound Pr1 assay. Percentage germination of conidia at 24 h was high (95-100%). Both immersion bioassay and spore bound Pr1 assay showed that inocula made from all substrate grains were virulent with those from millet being significantly (P=0.05) more virulent. Millet would be a cheaper substitute to rice previously recommended as solid substrate for mass production of M. anisopliae

Effects of temperature, relative humidity and duration of wetness period on germination and infection by conidia of the pear scab pathogen (Venturia nashicola)

Experiments were conducted to determine the effects of temperature, relative humidity (RH) and duration of wetness period on in vitro germination of conidia and infection of detached pear leaves by Venturia nashicola, the causal agent of pear scab. Conidia germinated only in near‐saturation humidity (RH &gt; 97%). The final percentage germination (24 h after inoculation) at 100% RH without free water was less than half that in free water. Conidia germinated over the range of temperatures tested (5–30°C); the optimum temperature for germination was ≈21°C. Changes in percentage germination of conidia over time were fitted by logistic models at each individual temperature. Polynomial models satisfactorily described the relationships between two (rate and time to 50% of maximum germination) of the three logistic model parameters and temperature. The minimum length of the wetness period for successful infection of detached pear leaves by conidia was observed at several temperatures. The shortest length of wetness period required for infection was 7 h at 22°C. Two polynomial models fitted well the relationship between the minimum wetness duration required for infection, and temperature.

A Role for Iron in Germination of Conidia of Colletotrichum musae

The time course of germination of conidia of Colletotrichum musae in the presence of different germination stimulants is consistent with the postulate that the stimulation of germination by anthranilic acid can be attributed to its previously established conversion to 2,3-dihydroxybenzoic acid in conidia. The activity of a number of synthetic chelating agents, such as EDTA and 1,10-phenanthroline, in promoting germination of the same order as 2,3-dihydroxybenzoic acid at about the same molarity provides support for the hypothesis that the chelating properties of the latter compound are important in its biological action. Experiments with conidia produced on media of different iron concentrations indicate that in the absence of a germination stimulant there is a high inverse correlation between the percentage germination of conidia and conidial iron content. However, in the presence of anthranilic acid there is no significant correlation between these parameters, percentage germination remaining uniformly high regardless of the conidial iron concentration. It is concluded that conidial iron is involved in the inhibition of germination and that this inhibition can be relieved non-specifically by a variety of chelating agents.

Competition for exogenous substrates in vitro by leaf surface micro-organisms and germination of conidia of Botrytis cinerea

A leaf surface bacterium, Pseudomonas sp. isolate 14, much more rapidly removed amino acids from solutions containing a mixture of amino acids than did conidia of Botrytis cinerea. Total uptake of amino acids was slightly greater when the bacterium and conidia were grown separately than when grown together. Conidia took up sugars more readily than the bacterium but sugars, in the absence of amino acids, caused little stimulation of germination. Both conidia and the bacterium took up glucose more readily in the presence of amino acids. Inhibition of germination of conidia by Pseudomonas sp. isolate 14 was correlated with uptake of amino acids from amino acid/glucose solutions.but not directly with uptake of amino acids in the absence of glucose. Differences in the abilities of other leaf surface bacteria and of yeasts to inhibit germination of conidia was associated with their respective capacities to take up amino acids from amino acid/glucose solutions. A highly significant negative correlation was obtained when uptake of amino acids by different leaf surface micro-organisms was plotted against percentage germination of conidia.

Long-term cryogenic storage of Neurospora crassa spores

Neurospora crassa on agar slants in ampules were frozen by direct immersion into liquid nitrogen and stored at −196 °C for 0–5.5 years. The survival, estimated as percentage germination of conidia, after warming, varied between 81.1 and 97.6%. Although there was a slight decline in survival immediately after the freezing treatment, no further significant decline has been detected during 5.5 years storage. The regression coefficients, (0.43, control, and 0.97, liquid nitrogen storage for 5.5 years), do not predict extinction of viability.

Temperature relations of powdery mildews

The optimum temperature for powdery mildews (Erysiphaceae) as a group is about 21° C, or 4 degrees lower than the average optimum for plant pathogens. Among the powdery mildews the optima for different species are about as follows: Erysiphe graminis, 17° C; E. polygoni, 23°; E. cichoracearum, 22°; Sphaerotheca pannosa, 24°; Uncinula necator, 26°; and Podosphaera leucotricha, 16°. The five criteria of fungus activity used to assay the relation of temperature to powdery-mildew development—number of conidia per conidiophore, rate of maturation of conidia, percentage germination of conidia, length of germ tubes in vitro, disease development, and length of hyphae in vivo—are considered to be of increasing merit in the order given. Powdery-mildew conidia are shorter-lived than the spores of most fungi: they live only about 2 days in ordinary environments. At lower and higher temperatures they live for longer and shorter times, respectively. Attached spores in situ live longer than detached spores on glass. Fresh conidia on the host surface are more tolerant of high temperature than are the young colonies resulting from the growth of these conidia.

STUDIES ON THE PHYSIOLOGY OF ELSINOE VENETA

A study was made of the effect of certain nutritional and environmental factors on the growth and pigmentation of the mycelium, the sporulation, and the germination of the conidia of a "convoluted" isolate of Elsinoe veneta (Burkh.) Jenkins, the fungus responsible for the anthracnose disease of raspberries. This isolate utilized with varying degrees of efficiency various mono-, oligo-, and polysaccharides as well as certain organic alcohols as its sole source of carbon for growth. Either a nitrate, ammonium, amino, or imidazole nitrogen compound supported the fungus in culture. Maximum growth of the mycelium occurred in the presence of soluble starch and asparagine, whereas optimum sporulation of the conidia was obtained on media containing potato starch and sodium nitrate. In general, the production of conidia was markedly reduced on media favorable for excessive vegetative growth. Both a decrease in the volume of the medium and in the concentration of either a specific nutrient or of total nutrients adversely influenced the production of mycelium. Temperatures above 30 °C. and below 21 °C. decreased the percentage germination of conidia and restricted the growth of the fungus. Growth and sporulation occurred over a wide range of pH values. The optimum initial pH for both growth and sporulation was 4.0. E. veneta produced conidia and grew as well in continuous darkness as in alternate diffuse light and darkness. Young potted raspberry plants growing in the greenhouse, when inoculated with conidia produced in culture, developed typical anthracnose lesions on the canes.