Ascospore Germination Research Articles

The Effects of Fungicides onEutypa lataGermination, Growth, and Infection of Grapevines

The fungicides benomyl, fenarimol, flusilazole, iprodione, myclobutanil, triadimefon, and vinclozolin were evaluated for their efficacy in vitro against Eutypa lata. For inhibition of ascospore germination, flusilazole was most effective, with an EC 50 value of 0.06 μg a.i./ml. Fenarimol and myclobutanil were somewhat less effective, with EC 50 values near 1 μg/ml. Benomyl, iprodione, triadimefon, and vinclozolin did not effectively inhibit germination. Flusilazole was also the most effective fungicide for inhibition of mycelial growth (.)

Protein synthesis during germination of heterothallic yeast ascospores.

Protein synthesis during ascospore germination of the heterothallic Saccharomyces cerevisiae strain AP-3 was investigated. Protein synthesis in the germinating ascospores appeared to begin approximately 20 min following glucose initiation. Since RNA synthesis did not start until approximately 70 min after the onset of germination, strain AP-3 ascospores must contain RNA which is ready for immediate translation. Both trehalase and glyceraldehyde-3-phosphate dehydrogenase activities were found to be affected by the onset of germination. Trehalase activity was found to increase severalfold following 60 min of spore germination but remained relatively constant over the subsequent 120 min examined. Dehydrogenase activity was not detectable in AP-3 ascospores but was measurable in germinating ascospores.

Epiphytic colonization of dry edible bean by bacteria antagonistic to Sclerotinia sclerotiorum and potential for biological control of white mold disease

Abstract Bacteria isolated from blossoms of dry edible bean (Phaseolus vulgaris) were evaluated for their potential as biological control agents against white mold disease of dry bean, caused by Sclerotinia sclerotiorum. Of the 10 isolates from blossoms tested, Erwinia herbicola strain B1 and Bacillus polymyxa strain B8 inhibited mycelial growth of S. sclerotiorum on agar media. When applied to detached blossoms, both strains reduced the germination of ascospores of S. sclerotiorum to approximately 40% compared to 69% in the control and inhibited the growth of germ tubes. In a growth chamber efficacy test, pretreatment of bean blossoms with either bacterial strain prevented the colonization of blossoms by the pathogen and the subsequent development of white mold lesions on the stems. The bacteria were applied to bean foliage in three field experiments to examine their population dynamics in the bean canopy and the ability to control white mold disease. E. herbicola B1 survived on inoculated bean leaves for 4 weeks after a single application at mean population levels exceeding log 4 colony-forming units (CFU) per leaf. Over 70% of the blossoms sampled from B1-treated plants during the same period were colonized by bacteria with the colony morphology of strain B 1, with mean populations exceeding log 4 CFU/blossom. Strain B1 significantly reduced the severity of white mold in one experiment in which it was applied three times and when the disease pressure was relatively low, as evident from the disease severity in the nontreated control (25%). However, B1 had no effect in two experiments in which there was a greater severity of white mold in the controls (>44%) and the bacterium was applied once. As there was little difference between single applications and three weekly applications in populations of B 1-type bacteria detected, efficacy may have been affected to a greater extent by the amounts of white mold disease than by plant colonization by the bacteria. In contrast, B. polymyxa strain B8 survived on leaves and was not detected on treated blossoms 1 week after application. As a consequence, it had no effect on white mold severity in any of the field experiments. Hence, the antagonist strains, while effective in inhibiting pathogen mycelial growth in vitro and colonization of blossoms in growth chamber tests, had limited efficacy in the field, particularly when disease pressure was moderate to high.

Interactions between Sclerotinia sclerotiorum and Epicoccum purpurascens

Sterile culture filtrates of Epicoccum purpurascens decreased severity of white mold of bean and increased pod yield when applied prior to inoculation of beans with Sclerotinia sclerotiorum. Extracts of these culture filtrates inhibited ascospore germination and mycelial growth of S. sclerotiorum. Similar inhibition of hyphal growth of S. sclerotiorum occurred when dual cultured with E. purpurascens. Contact and penetration of hyphae of S. sclerotiorum by hyphae of E. purpurascens occurred rarely on agar-covered slides and was not observed on flower petals. Inhibition of ascospore germination and germ-tube elongation occurred on agar-covered slides where E. purpurascens had been grown previously; however, addition of nutrients decreased inhibition. Colonization of bean flowers by E. purpurascens reduced white mold incidence. The degree of disease control was affected by addition of nutrients and whether or not colonized flowers were autoclaved. Key words: antifungal compounds, competition, biological control, white mold, Phaseolus.

Microcyclic Conidiation Cycles in Epichloe typhina

Germination of ascospores in Epichloe typhina was described earlier as iterative germination in which each part spore of an ascospore germinated and produced conidia without an intervening mycelial phase. In the present study it was determined that the conidia produced by iterative germination also undergo an additional series of microcyclic conidiations. Thus, conidia produced from the ascosporic microcyclic structure germinated and produced other conidia, which also germinated producing yet another microcyclic structure. It was only after the third stage of microcyclic conidiations that mycelial development occurred. Microcycle conidiation in E. typhina is viewed as an obligate developmental sequence since no alternative process was observed. This distinguishes it from microcycle conidiation reported in other fungi where microcycle conidiation is facultative, being inducible only under certain laboratory conditions. Although unexplored, microcyclic conidiation may be a fundamentally important aspect of the life history of E. typhina and a variety of other fungi.

A site-specific deletion in mitochondrial DNA of Podospora is under the control of nuclear genes.

In the filamentous fungus Podospora anserina, the association of two nuclear genes inevitably leads to a "premature death" phenotype consisting of an early end of vegetative growth a few days after ascospore germination. Mycelia showing this phenotype contain a mitochondrial chromosome that always bears the same deletion. One of the break points is exactly at the 5' splice site of a particular mitochondrial intron, suggesting that the deletion event could result from molecular mechanisms also involved in intron mobility. One of the nuclear genes involved in triggering this site-specific event belongs to the mating-type minus haplotype; the other is a mutant allele of a gene encoding a cytosolic ribosomal protein.

Biology and pathogenicity of Rosellinia desmazieresii

Rosellinia ring-dying of Salix repens occurs in dry slacks at Ainsdale Nature Reserve in Lancashire. Studies on Rosellinia desmazieresii demonstrated that environmental conditions in these dry slacks during periods of the year when new disease rings appear correspond to those favourable for the growth and development of this pathogen. The optimum temperature for ascospore germination and mycelial growth was around 20 °C. R. desmazieresii modified the pH of unbuffered culture media and under buffered conditions germination and growth were optimal at pH 6. The population of S. repens at Ainsdale Nature Reserve exhibited some heterogeneity in susceptibility to this fungus, and a naturally-occurring hybrid, Salix × Friesiana was highly resistant to infection. Host range studies conducted with selected coniferous and broad-leaved woody species indicated that Fagus sylvatica and a Larix sp. were also susceptible to this pathogen.

Influence of Temperature and Moisture on Germination of Ascospores and Conidia ofBotryosphaeria dothidea

Predicted optimum temperatures for germination of conidia of isolates 1, 2, and 3 of Botryosphaeria dothidea in free water were 26.7, 27.8, and 29.5 C. Conidia ofisolates and 2 germinated at 8 C after 24 hr but none from isolate 3 germinated. Conidia of isolate 1 incubated at 95-100% relative humidity (RH) germinated after 12 hr, the percent germination declined with RH. Few conidia of isolates 2 or 3 germinated in the absence of free water. The predicted optimum temperature for ascospore germination was 24.6 C

Biological Control ofEutypa lataon Grapevine by an Antagonistic Strain ofBacillus subtilis

An isolate of Bacillus subtilis from grapevine wood inhibited in vitro growth of Eutypa lata, the causal organism of dieback in grapevines. On potato-dextrose agar, the bacterium caused 91.4% inhibition of mycelial growth of E. lata and 100% inhibition of ascospore germination. Ascospore germination correlated negatively with time of exposure to B. subtilis. Malformation of hyphae of E. lata occured in the presence of B. subtilis. At a concentration of ≥0.8 mg/ml, an antibiotic substance in an ethanol extract from B subtilis totally inhibited germination of ascospores E. lata (...)

Powdery Mildew of Sweet Cherry: Influence of Temperature and Wetness Duration on Release and Germination of Ascospores ofPodosphaera clandestina

The effects of temperature and wetness duration on release and germination of ascospores of Podosphaera clandestina, causal agent of sweet cherry powdery mildew, were determined in controlled-environment studies. Ascospore release occurred in the presence of free water at temperatures between 5 and 30 C and at wetness durations as short as 1 h. Spore release increased rapidly between 2 and 4 h wetness durations, and after 8 h was optimal at 15-20 C (...)

Kathistes, a new genus of pleomorphic ascomycetes

The genus Kathistes is described to accomodate two new species, K. calyculata and K. analemmoides, and an existing one based on Pyxidiophora fimbriata Barrasa & Moreno. All three species are coprophilous and produce transversely septate ascospores in long-necked perithecia. Ascospore germination occurs by the production of budding yeast cells. Sporelike bodies, termed sporidiolae, are produced in spherical structures resembling the perithecia called sporidiomata. Similar genera and species are discussed and contrasted by a dichotomous key. Kathistes species do not appear to be closely related to other ascomycetes and are assigned to a new family Kathistaceae.

Ascospore germination and appressorium formation in vitro of some species of the Rhytismataceae

Ascospore germination and appressorium formation were examined in Cyclaneusma minus, Lirula macrospora Lirula sp., Lophodermium arundinaceum, L. juniperinum, L. piceae, L. pini-excelsae, L. pinastri, L. seditiosum and Meloderma desmazieresii. All species except C. minus formed appressoria after 12–24 h incubation. Sizes and forms of appressoria are typical and specific for each species, and can be used as an additional morphological character for identification. Observations and possible reasons for disturbance of ascospore germination and failures in single spore isolations are discussed.

Morphological, Cultural and Mating Studies on Atkinsonella, Including A. Texensis

Comparative morphological and cultural studies in strains of Atkinsonella (Clavicipitaceae, tribe Balansieae) from all known host grasses {Danthonia compressa, D. spicata, D. sericea and Stipa leucotricha) revealed a number of characteristics distinguishing between strains from the allopatric host genera Danthonia and Stipa. Differences were found in stroma size, in morphology of the Ephelis anamorph, and in growth rates and colony characteristics in culture. The Stipa form of Atkinsonella is recognized as a separate species, A. texensis. Conidial transfers between stromata from different clones of D. spicata indicated a heterothallic mating system in A. hypoxylon. Distinctive characteristics of Atkinsonella, including ascospore germination pattern, warrant recognition of Atkinsonella as a distinct genus from Balansia.

Antagonism of white mold (Sclerotinia sclerotiorum) of bean by fungi from bean and rapeseed flowers

Filamentous fungi from white bean and rapeseed flowers were isolated, characterized, and evaluated for potential as antagonists to Sclerotinia sclerotiorum (Lib.) de Bary. Various fungi were isolated from surface-sterilized petals sampled from four developmental stages ranging from freshly opened flowers to petals that had lodged on plant surfaces. Alternaria and Cladosporium spp. were the dominant mycoflora and were isolated from 65–100% of the petals that developed fungal colonies. All isolates, except one, restricted ascospore germination by the pathogen on water agar by 16–66%, and 13 of 28 isolates restricted mycelial growth on potato dextrose agar by 29–46%. Bean flowers were inoculated with spore suspensions of S. sclerotiorum and of individual antagonists and were then placed on detached bean leaves, bean seedlings, and flowering bean plants. On detached leaves in a laboratory environment, 16 of 28 isolates suppressed white mold lesion diameter by 10–100%. On bean seedlings in a growth room, 8 isolates suppressed the percentage of flowers developing lesions by 42–100%, and 12 of 13 isolates reduced mean lesion diameter by 14–100%. On flowering bean plants in a greenhouse, 6 of 11 isolates suppressed the percentage of flowers developing lesions by 14–90 %. The most disease-suppressive fungi included isolates of Drechslera sp., Epicoccum purpurascens, Fusarium graminearum, and Fusarium heterosporum; isolates of Myrothecium verrucaria and Trichoderma viride were effective in some trials.

Growth and fumitremorgin production by Neosartorya fischeri as affected by food preservatives and organic acids

The effects of potassium sorbate, sodium benzoate, sulphur dioxide and citric, malic and tartaric acids on growth and fumitremorgin production by a heat‐resistant mould, Neosartorya fischeri, cultured on Czapek yeast autolysate agar (CYA) were studied over a 32‐day incubation period. Colonies were examined, and extracts of agar and mycelia were analyzed for mycotoxin content using high performance liquid chromatography (HPLC). Growth of N. fischeri always resulted in production of the fumitremorgins verruculogen and fumitremorgin A and C. Growth on CYA (pH 3.5) was highly repressed by potassium sorbate and sodium benzoate; 75 mg/1 completely inhibited germination of ascospores. Sulphur dioxide was less inhibitory; growth occurred on CYA containing 100 but not 200 mg/1. Growth of N. fischeri was significantly reduced when the pH of CYA was reduced from 7.0 to 4.5 to 3.5 to 2.5. Citric, malic and tartaric acids promoted growth and fumitremorgin production when supplemented to CYA (pH 2.5). These observations indicate that growth and fumitremorgin production by N. fischeri are influenced by pH and type of acid present and can be controlled by small amounts of preservatives.

Influence of Temperature and Moisture on Germination of Ascospores and Conidia ofBotryosphaeria obtusa

Requirements for ascospore germination were similar to those for conidia. Germ tube lengths of ascospores and conidia were maximum in free water and decreased with decreasing relative humidity. After 12 hr in free water, ascospore germ tubes reached a maximum mean length of 0.78 mm at 28 C, whereas maximum conidial germ tube length was 0.82 mm at 24 C for isolate 087 and 0.99 mm at 28 C for isolate 049. Germ tube length of both types of spores declined at 32 C

Ascospore Production, Release, Germination, and Infection ofPopulusbyMycosphaerella populorum

Ascospore production, as measured by a liberation tunnel, and ascospore release, as detected by Vaseline-coated slide traps, peaked in mid- to late May and continued for 3-4 mo after initial release. Peak ascospore release in the field corresponded to peak periods of foliar and stem infection of the two clones of Populus. Stems of the moderately resistant clone were infected only in May, whereas foliar and stem infection of the susceptible clone occurred periodically throughout the growing season

Effects of Sulphur Dioxide and Fluoride on Ascospore Germination of Several Lichens

AbstractThe effects of fluoride and sulphur dioxide on the germination of ascospores of Lecanora conizaeoides, Xanthoria parietina, Physconia distorta and Peltigera canina were studied under controlled conditions. The two pollutants (H2SO3 and NaF) were dissolved in the culture medium. An improved culture technique permitted a high percentage germination (90° 0) of P. canina spores. Peltigera canina spores had the highest sensitivity to SO2 (no germination at 500 UM H2SO3). Lecanora conizaeoides spores were almost insensitive to each of the two studied pollutants (30°0 spore germination at 1000 UM H2SO3 or NaF). However, simultaneous exposure to 1000 UM H2SO3 and 1000 UM NaF resulted in no germination, indicating a synergistic effect of these products.

Evolutionary Aspects of Ascospore and Conidium Ontogeny in Scoleconectria cucurbitula

Morphological changes and nuclear behavior during ascospore ontogeny in a collection of Scoleconectria cucurbitula with two-spored asci were characterized, and asexual states observed in artificial culture. Following meiosis, two single-celled, uninucleate ascospores were formed within the developing ascus; the other two post-meiotic nuclei did not take part in ascospore development. Ascospores progressed through two-celled, four-celled, and multi-celled stages, finally becoming highly elongate and transversely septate, with numerous uninucleate cells. While within the ascus, ascospore cells differentiated into phialides and produced numerous conidia. Synanamorphs formed in culture included a phialidic hyphomycetous state, a pycnidial state, and a state producing spores within hyphal cells by a process resembling free cell formation. It is suggested that intra-ascal germination obviates the need for greater numbers of ascospores, and that the two-spored form of S. cucurbitula likely arose from the four-spored form. Intra-ascal germination appears correlated with loss of ascus rings and possibly with loss of forcible spore discharge in certain Nectria species. The possible role of heterochrony in the evolution of phialidic ascospore germination in S. cucurbitula and allied fungi is discussed.

Evolutionary Aspects of Ascospore and Conidium Ontogeny in Scoleconectria Cucurbitula

Morphological changes and nuclear behavior during ascospore ontogeny in a collection of Scoleconectria cucurbitula with two-spored asci were characterized, and asexual states observed in artificial culture. Following meiosis, two single-celled, uninucleate ascospores were formed within the developing ascus; the other two post-meiotic nuclei did not take part in ascospore development. Ascospores progressed through two-celled, four-celled, and multi-celled stages, finally becoming highly elongate and transversely septate, with numerous uninucleate cells. While within the ascus, ascospore cells differentiated into phialides and produced numerous conidia. Synanamorphs formed in culture included a phialidic hyphomycetous state, a pycnidial state, and a state producing spores within hyphal cells by a process resembling free cell formation. It is suggested that intra-ascal germination obviates the need for greater numbers of ascospores, and that the two-spored form of S. cucurbitula likely arose from the four-spored form. Intra-ascal germination appears correlated with loss of ascus rings and possibly with loss of forcible spore discharge in certain Nectria species. The possible role of heterochrony in the evolution of phialidic ascospore germination in S. cucurbitula and allied fungi is discussed.