Ascigerous Stage Research Articles

The peculiarities for developing of apple scab’s pathogens in ascigerous stage and the disease expression in Western Forest-Steppe of Ukraine

The researches results for ascospore stage causative agent and disease appearing in Western Forest-steppe of Ukraine were provided.

Risk Factors for Bud Perennation of Podosphaera macularis on Hop.

The hop powdery mildew fungus Podosphaera macularis persists from season to season in the Pacific Northwestern United States through infection of crown buds because only one of the mating types needed to produce the ascigerous stage is presently found in this region. Bud infection and successful overwintering of the fungus leads to the emergence of heavily infected shoots in early spring (termed flag shoots). Historical data of flag shoot occurrence and incidence in Oregon and Washington State during 2000 to 2017 were analyzed to identify their association with the incidence of powdery mildew, growers' use of fungicides, autumn and winter temperature, and other production factors. During this period, flag shoots were found on 0.05% of plants evaluated in Oregon and 0.57% in Washington. In Oregon, the incidence of powdery mildew on leaves was most severe and the number of fungicide applications made by growers greatest in yards where flag shoots were found in spring. Similarly, the incidence of plants with powdery mildew in Washington was significantly associated with the number of flag shoots present in early spring, although the number of fungicide applications made was independent of flag shoot occurrence. The occurrence of flag shoots was associated with prior occurrence of flag shoots in a yard, the incidence of foliar powdery mildew in the previous year, grower pruning method, and, in Washington, winter temperature. A census of hop yards in the eastern extent of the Oregon production region during 2014 to 2017 found flag shoots in 27 of 489 yards evaluated. In yards without flag shoots, 338 yards (73.2%) were chemically pruning or not pruned, whereas the remaining 124 (26.8%) were mechanically pruned. Of the 27 yards with flag shoots, 22 were either chemically pruned or not pruned and 4 were mechanically pruned in mid-April, well after the initial emergence of flag shoots. The prevalence of yards with flag shoots also was related to thoroughness of pruning in spring (8.1% of yards with incomplete pruning versus 1.9% of yards with thorough pruning). A Bayesian logistic regression model was fit to the data from the intensively assessed yards in Oregon, with binary risk factors for occurrence of a flag shoot in the previous year, occurrence of foliar mildew in the previous year, and thoroughness of pruning in spring. The model indicated that the median and 95% highest posterior density interval of the probability of flag shoot occurrence was 0.0008 (0.0000 to 0.0053) when a yard had no risk factors but risk increased to 0.0065 (0.0000 to 0.0283) to 0.43 (0.175 to 0.709) when one to all three of the risk factors were present. The entirety of this research indicates that P. macularis appears to persist in a subset of chronically affected hop yards, particularly yards where spring pruning is conducted poorly. Targeted management of the disease in a subset of fields most at risk for producing flag shoots could potentially influence powdery mildew development regionwide.

First Report of Anthracnose Fruit Rot of Strawberry Caused by Colletotrichum acutatum in Montenegro.

Strawberries (Fragaria × ananassa) in Montenegro have become an increasingly important economic crop in recent years. During May 2011, severe fruit damage in strawberry cv. Clery was observed in two fields in the Podgorica region. Fruit symptoms were typical for strawberry anthracnose: sunken, dark brown to black circular lesions appeared on maturing fruits. However, no stem, crown, or foliar symptoms were observed. Under wet conditions, orange masses of conidia were produced in acervuli in the center of lesions. Conidia were hyaline, aseptate, cylindrical, with pointed ends, measuring 9.8 to 17.2 (mean 14.3) × 2.5 to 6.1 (mean 4.4) μm. Colonies on potato dextrose agar (PDA) were initially white, then turned gray as conidia formed in orange to salmon pink masses around the center of the culture. Setae or an ascigerous stage were never observed in culture or on the host. Koch's postulates were fulfilled by inoculating ripe and unripe asymptomatic fruits (20 of each, removed from strawberry plants cv. Clery) with the isolated fungus. Fruits were sprayinoculated (106 conidia/ml). An equal number of noninoculated fruits were used as a control. After incubation time of 2 to 3 days at 25°C in a moist chamber, symptoms appeared on inoculated ripe fruits. On unripe fruits, the lesions developed only 3 to 4 days after the inoculation. No symptoms were found on control fruits. The fungus was reisolated from fruits, after which typical morphological characteristics developed in culture as described above. On the basis of the symptoms, the morphological and cultural characteristics of the fungus, and the pathogenicity test, the disease was identified as strawberry anthracnose caused by Colletotrichum acutatum, which is in accordance with previous reports (1,2,3,4). The isolate was submitted to the Centraalbureau voor Schimmelcultures in the Netherlands (CBS 131813). The internal transcribed spacer (ITS) region of the fungal DNA was amplified with ITS1F and ITS4 primers, sequenced, and submitted to NCBI GenBank (Accession No. JQ424934). BLASTn searches of GenBank using the ITS sequence revealed 99% similarity with database sequences of C. acutatum. Since the pathogen was found in the main Montenegrin strawberry production area, it poses a threat to strawberry production in Montenegro. To our knowledge, this is the first report of anthracnose fruit rot of strawberry in Montenegro.

Effects of Prior Vegetative Growth, Inoculum Density, Light, and Mating on Conidiation of Erysiphe necator

Initiation of asexual sporulation in powdery mildews is preceded by a period of superficial vegetative growth of mildew colonies. We found evidence of a quorum-sensing signal in Erysiphe necator that was promulgated at the colony center and stimulated conidiation throughout the colony. Removal of the colony center after putative signal promulgation had no impact upon timing of sporulation by 48-h-old hyphae at the colony margin. However, removal of the colony center before signaling nearly doubled the latent period. A relationship between inoculum density and latent period was also observed, with latent period decreasing as the number of conidia deposited per square millimeter was increased. The effect was most pronounced at the lowest inoculum densities, with little decrease of the latent period as the density of inoculation increased above 10 spores/mm. Furthermore, light was shown to be necessary to initiate conidiation of sporulation-competent colonies. When plants were inoculated and maintained in a day-and-night cycle for 36 h but subjected to darkness after 36 h, colonies kept in darkness failed to sporulate for several days after plants kept in light had sporulated. Once returned to light, the dark-suppression was immediately reversed, and sporulation commenced within 12 h. Merging of colonies of compatible mating types resulted in near-cessation of sporulation, both in the region of merging and in more distant parts of the colonies. Colonies continued to expand but stopped producing new conidiophores once pairing of compatible mating types had occurred, and extant conidiophores stopped producing new conidia. Therefore, in addition to a quorum-sensing signal to initiate conidiation, there appears to be either signal repression or another signal that causes conidiation to cease once pairing has occurred and the pathogen has initiated the ascigerous stage for overwintering.

First Report of Anthracnose Fruit Rot Caused by Colletotrichum acutatum on Strawberry in Korea

Symptoms typical of anthracnose fruit rot; sunken, dark brown lesions on maturing fruits, were found in a commercial field of strawberry (Fragaria × ananassa) cv. Cal Giant in Yangyang County, Korea in May 2007. Masses of conidia were produced in acervuli in the center of lesions. The fungus was isolated on potato dextrose agar (PDA). Colonies grown on PDA were pale to mouse gray and became dark green to black in reverse. Conidia were formed in orange-to-salmon pink masses in the center of the culture. The average size of conidia on PDA was 15.2 × 4.6 μm, and they were hyaline, straight, cylindrical, with pointed ends, and aseptate (1). The fungus did not form an ascigerous stage in culture. Mycelial growth rate was 7.5 mm per day at 25°C on PDA. The identity of two isolates was confirmed as Colletotrichum acutatum J.H. Simmonds by PCR amplification using species-specific primers TBCA and TB5 (2), resulting in a characteristic 330-bp band on agarose gel. Morphological characters were in accordance with previous reports on C. acutatum. A pathogenicity test was conducted with five healthy plants of cvs. Cal Giant, Maehyang, Seolhyang, Kumhyang, Akihime, and Redpearl. After fruits and flowers were sprayed with a conidia suspension (105 conidia per ml), the plants were maintained at 10 to 25°C and 100% relative humidity in a greenhouse. As a control, five healthy plants were sprayed with sterile distilled water and incubated under the same conditions. Dark brown, water-soaked spots appeared on mature fruits of all cultivars after 5 days, and lesions on green fruits appeared on individual achenes. Flowers developed dark lesions, dried out, and died. No symptoms were found on the control plants. After the pathogen was reisolated from fruits and flowers lesions, the morphological characters developed in culture as described above. To our knowledge, this is the first report of C. acutatum causing strawberry anthracnose in Korea.

Glomerella acutata on Highbush Blueberry (Vaccinium corymbosum L.) in Norway

In August 2004, Glomerella acutata Guerber & Correll was detected on fruits from highbush blueberry (Vaccinium corymbosum L.) for the first time in Norway. Both the conidial (Colletotrichum acutatum J. H. Simmonds) and the ascigerous (G. acutata) stage developed on naturally infected blueberry fruits. Perithecia also readily formed on blueberries and strawberries inoculated with a culture from highbush blueberry, and on artificial, solid medium (both on strawberry leaf agar and potato dextrose agar). To our knowledge this is the first report worldwide of the teleomorph of Glomerella acutata on a naturally infected host. Accepted for publication 15 January 2007. Published 9 May 2007.

First Report of Anthracnose Fruit Rot of Strawberry Caused by Colletotrichum acutatum in China.

In 2004, fruits showing dark and sunken necrotic lesions were observed on strawberries (Fragaria × ananassa Duch. cv. Mei No. 3) in a field in Shanghai, China. All isolates obtained from the infected fruits easily produced orange spore masses and developed orange colonies with orange reverse colony color; none formed setae or the ascigerous stage in culture or on the host. The conidia were hyaline, straight and fusiform, 8 to 16 × 2.5 to 4 μm, and produced melanized, ellipsoid, ball- or pear-shaped appressoria at the end of germ tubes. These isolates were similar to those described for Colletotrichum acutatum J. H. Simmonds. To confirm pathogenicity of the isolate, inoculum suspension with 4 × 106 conidia/ml was sprayed onto 10 fruiting strawberry plants until runoff. The inoculated plants were maintained at 25°C and 100% relative humidity in a growth chamber with a 12-h period of fluorescent light daily. Plants inoculated with sterilized water were controls. After 3 days, dark brown lesions appeared in the leaves, petioles, and fruits of all inoculated plants. The symptoms were similar to those observed on the strawberry fruit from which the isolate was originally isolated. The pathogen was consistently reisolated from the symptomatic fruit. No symptoms were observed on the control plants. To our knowledge, this is the first report of C. acutatum as the casual agent of anthracnose fruit rot of strawberry in China.

The Perfect Stage of Powdery Mildew of Sugar Beets Found in Idaho and Colorado.

Powdery mildew (Erysiphe polygoni DC [synonym E. betae {Vanha} Weltzien]) of sugar beet (Beta vulgaris L.) has been a significant problem in many sugar beet growing areas of the United States since the first serious epidemic in 1974. Disease has been attributed solely to the asexual stage of the pathogen in the United States, except for one report of the perfect stage in a single field in Washington coincidental with the 1974 epidemic (1). In August 2001, ascomata were observed in several fields in Owyhee County in southwestern Idaho near Grand View. The perfect stage was widespread and easily found, and in one field the surfaces of leaves collected from 50 randomly sampled plants were between 10 and 90% covered with ascomata. Subsequently, the ascigerous stage was found in September and October in multiple fields in three additional counties in southwestern and south-central Idaho and two counties in northern Colorado. Ascomata were found on 12 commercial varieties in the two states and six breeding lines in Colorado. Asci contained one to four hyaline or yellow-to-golden pigmented ascospores per ascus. Ascomata observed in Idaho and Colorado are similar to those described from Europe (2). Ascospores appeared intact after leaves were dried and stored at 4 to 7°C more than 4 weeks. However, after leaves with ascomata were dried and stored at 24 to 27°C for 1 week or more, ascomata and asci appeared intact microscopically, but ascospores were no longer delineated and appeared desiccated or degraded. Because the ascigerous stage provides a means of genetic recombination, there is the potential for races of the pathogen to arise with greater frequency. This has serious implications for managing fungicide resistance and breeding for disease resistance to sugar beet powdery mildew.

First Report of Colletotrichum acutatum in Strawberry in Norway.

Anthracnose caused by Colletotrichum acutatum J. H. Simmonds was detected in strawberry (Fragaria × ananassa Duch.) for the first time in Norway in 1999. Symptoms were found in greenhouse grown strawberries in the cultivar Korona. Symptoms were typical of strawberry anthracnose: sunken, brown, and firm lesions appeared on maturing fruits. Masses of conidia were produced in acervuli in the center of lesions. The fungus was isolated on acidified potato dextrose agar. Colonies grown on potato dextrose agar (PDA) were pale to mouse gray and became dark greenish to blackish in reverse. Conidia were formed in orange to salmon pink masses in the center of the culture. Conidia in cultures were 16.5 (13.8 to 18.8) × 4.5 (3.8 to 5) μm, and were hyaline, cylindrical, with pointed ends, and aseptate. Setae were never observed in culture or on fruits. The fungus did not form an ascigerous stage in culture. Mycelial growth rate at 25 to 26°C on PDA was 8.1 to 8.4 mm per day. Morphological characters and growth rate were in accordance with previous reports on C. acutatum (1,2). The isolated fungus was confirmed to be C. acutatum by both the International Mycological Institute, Egham, England, and Centraalbureau voor Schimmelcultures, Baarn, the Netherlands. Koch's postulates were fulfilled by inoculating ripe and unripe fruits on strawberry plants with the isolated fungus. Fruits were either sprayed with a conidial suspension (106 conidia per ml) or slightly wounded with a needle that had been dipped in a conidial mass from a pure culture of C. acutatum. Symptoms appeared after 4 days at 20°C, and after 5 days, brown, sunken, circular lesions reached a size of 1 cm in diameter on wounded, ripe fruits. In unripe fruits the lesions developed more slowly, and in unwounded fruits sprayed with a conidial suspension, large, irregular spots developed. Leaves were inoculated by placing a small block of agar at the base of petioles on intact strawberry plants. The tissue underneath the agar was either unwounded or slightly wounded with a needle. After 20 days (at 20 to 25°C) some necrosis developed on both unwounded and wounded petioles. No symptoms were observed in the crown tissue where the inoculated petioles were attached. The fungus was readily reisolated from both fruits and petioles, after which typical morphological characters developed in culture as described above.

Identity of Guignardia sp. inhabiting ericaceous plants

An ascomycete belonging to the genus Guignardia with a Phyllosticta anamorph was frequently isolated from living leaves of several ericaceous plants. Ecological study on assemblages of endophytes suggested that this fungus is a dominant endophytic fungus of ericaceous plants. The Phyllosticta anamorph was morphologically similar to Phyllosticta capitalensis P. Henn., which can be a pathogen of orchids. An authentic culture of P. capitalensis IFO 32914 (= CBS 226.77) produced an ascigerous stage on potato dextrose agar, the morphology of which was identical to the Guignardia sp. from ericaceous plants. Sequence data of the internal transcribed spacer regions of ribosomal DNA (ITS1 and ITS2, including 5.8S rDNA) supported the identity of the present fungus and P. capitalensis. Consequently, we describe this endophytic ascomycete found from ericaceous plants as Guignardia endophyllicola sp.nov., which has P. capitalensis as an anamorph. Previously known as a pathogen of orchids, the fungus was revealed to exist widely as an endophyte within ericaceous plants.Key words: endophytic fungus, Ericaceae, Guignardia endophyllicola, pathogenic fungus, Phyllosticta capitalensis, Orchidaceae.

Identity of <i>Guignardia</i> sp. inhabiting ericaceous plants

An ascomycete belonging to the genus Guignardia with a Phyllosticta anamorph was frequently isolated from living leaves of several ericaceous plants. Ecological study on assemblages of endophytes suggested that this fungus is a dominant endophytic fungus of ericaceous plants. The Phyllosticta anamorph was morphologically similar to Phyllosticta capitalensis P. Henn., which can be a pathogen of orchids. An authentic culture of P. capitalensis IFO 32914 (= CBS 226.77) produced an ascigerous stage on potato dextrose agar, the morphology of which was identical to the Guignardia sp. from ericaceous plants. Sequence data of the internal transcribed spacer regions of ribosomal DNA (ITS1 and ITS2, including 5.8S rDNA) supported the identity of the present fungus and P. capitalensis. Consequently, we describe this endophytic ascomycete found from ericaceous plants as Guignardia endophyllicola sp.nov., which has P. capitalensis as an anamorph. Previously known as a pathogen of orchids, the fungus was revealed to ex...

Frequency ofColletotrichumSpecies Causing Bitter Rot of Apple in the Southeastern United States

The occurrence and frequency of Colletotrichum spp. were determined by sampling 980 apple fruit from orchards in Arkansas, North Carolina, and Virginia in 1992 and 1993. Colletotrichum and Botryosphaeria spp. were recovered from 78.8 and 21.2% of the sampled fruit, respectively. Conidial and colony morphology, growth rate, and perithecial production were used to characterize the Colletotrichum spp. Based on conidial morphology, 68.6% of isolates were identified as C. acutatum and 31.4% as C. gloeosporioides. The C. acutatum isolates produced hyaline, elliptic-fusiform conidia tapered at one or both ends, whereas isolates of C. gloeosporioides produced hyaline oblong conidia with obtuse or rounded ends. Among the C. gloeosporioides isolates, 42.1% of monoconidial cultures produced the Glomerella cingulata teleomorph. None of the isolates identified as C. acutatum produced an ascigerous stage. All isolates of C. acutatum had a significantly slower growth rate on potato dextrose agar (PDA) than did isolates of C. gloeosporioides and G. cingulata. Among the isolates of C. acutatum, 90% were characterized as chromogenic types producing a distinct ruby red pigmentation on PDA. However, the ruby red colony color was not diagnostic for species identification as there were some isolates of C. acutatum that produced colonies orange to dark brown in color on PDA. The chromogenic isolates were only found among the isolates identified as C. acutatum. Of the Botryosphaeria spp. recovered, 84.1 and 15.9% of the isolates were identified as B. dothidea and B. obtusa, respectively. The majority of Botryosphaeria isolates were recovered from fruit with small (<0.5 cm in diameter), nondescript lesions. Among the bitter rot pathogens, three taxa, C. acutatum, C. gloeosporioides, and G. cingulata, could be distinguished. Based on this survey, there was considerable orchard-to-orchard variation in the frequency of the Colletotrichum spp. recovered.

Morphological, Cultural, and Pathogenic Variation Among Colletotrichum Species Isolated from Strawberry

Conidia, cultural characteristics, appressoria, and setae of 24 isolates of Colletotrichum species from strawberry were compared. The virulence of each isolate on plants of 14 strawberry cultivars and one breeding clone was evaluated. Thirteen isolates identified as C. fragariae produced cylindrical conidia; developed beige to olive to dark gray colonies, generally with dark olive to dark gray reverse colony colors; and did not form the ascigerous state in culture. Two isolates identified as Glomerella cingulata (anamorph: C. gloeosporioides) developed gray or olive-gray colonies with dark gray to dark olive reverse colony colors, produced cylindrical conidia, and formed the ascigerous state in culture. Nine isolates identified as C. acutatum produced fusiform conidia and developed pink, orange, rose, or beige colonies with predominantly cream, pink, or rose reverse colony colors; none formed an ascigerous stage in culture. C. acutatum isolates could be easily differentiated from C. fragariae and C. gloeosporioides isolates by their growth rate in plate culture on potato-dextrose agar. The greatest difference in growth rate occurred at 32 C, where the average diameter of 5-day-old C. acutatum cultures was 13 mm, compared with 69 mm for C. fragariae and 63 mm for C. gloeosporioides. All of the C. fragariae isolates induced disease symptoms when wound-inoculated into strawberry leaves and fruit, whereas all of the C. acutatum isolates caused fruit rot but none caused leaf lesions. All 13 of the C. fragariae, four of the five C. acutatum, and one of the two C. gloeosporioides isolates tested caused a crown rot of certain strawberry cultivars. Disease severity ratings after plant spray inoculations resulted in a highly significant isolate x cultivar interaction, suggesting that some isolates may represent different races among the tested isolates of C. fragariae and C. acutatum. Overall, C. fragariae isolates caused more severe petiole and crown symptoms than did C. acutatum isolates, which in turn caused more severe symptoms than did C. gloeosporioides isolates. However, some cultivars were more susceptible to certain C. acutatum isolates than to some C. fragariae isolates, e.g., the cultivar Sunrise was susceptible to C. acutatum isolates Goff and Mil-1 but resistant to C. fragariae isolate Fla-2.

Two species of phyllosticta with a common ascigerous stage on Sapindus

Two species of phyllosticta with a common ascigerous stage on Sapindus

The Ascigerous Stage of Blastomyces dermatitidis

The Ascigerous Stage of Blastomyces dermatitidis

The Ascigerous Stage of Blastomyces Dermatitidis

The Ascigerous Stage of Blastomyces Dermatitidis

Morphology and Cytology of Diplocarpon Maculatum on Crataegus. II. Initiation and Development of the Apothecium

In a previous communication (23), we reported on the development of the parasitic imperfect stage of the fungus inciting Entomosporium Leaf Spot of Hawthorn. The initiation, growth, and maturation of the ascocarps of this fungus will now be considered. Despite the widespread occurrence of Entomosporium infections on pomaceous hosts, the perfect stage of the causal organism appears to have been infrequently encountered, and no critical study of the origin and development of the apothecia has ever been published. Atkinson (2) in 1897 recorded having found, on overwintered quince leaves in New York, a discomycetous fungus which he believed to be the ascigerous stage of Entomosporium maculatum Lev. In 1909 (3) he was able to report the formation of Entomosporium conidia in pure cultures grown from ascospores of this discomycete, thus establishing the suspected relationship. He named the new cup fungus Fabraea maculata. In Germany, in 1906, Klebahn (16) found similar apothecia on overwintered pear leaves which had shown Entomosporium blighting the previous summer. In 1914 (16), apparently unaware of Atkinson's publications, he recorded this discomycete as the presumptive ascocarpic stage of E. maculatum and named it Entomopeziza soraueri, erecting a new genus for it because of its peculiar conidial phase. Later (17) Klebahn provided descriptions of apothecia from overwintered foliage of pear and quince, and stated that he had observed deep-seated fruiting bodies which resembled apothecia but which contained Entomosporiumtype spores instead of asci. He succeeded in obtaining pure cultures from these conidia and from ascospores, and found that cultures from both sources produced the typical cruciate conidia of Entomosporium. In New Zealand, Cunningham (6) was unable to find the perfect stage of Entomosporium. However, he studied Atkinson's type mate-

A new species of colletotrichum and its associated ascigerous stage

A new species of colletotrichum and its associated ascigerous stage

Hypomyces Stage of Fusarium solani f. pisi

ASCIGEROUS stages have not been established heretofore for either of the Fusarium pathogens of pea, Pisum sativum L., that is, for F. oxysporum f. pisi (Linf.) Snyd. and Hans., the cause of a vascular wilt, or F. solani f. pisi (Jones) Snyd. and Hans., the cause of a cortical foot and root disease. Evidence is presented in this communication that the ascigerous stage of the latter pathogen has been discovered and belongs to the genus Hypomyces. Although perfect stages are now known for several formae in F. solani, none has yet been established for any member of the species F. oxysporum.

A NEW SPECIES OF PHYLLOSTICTA AND ITS ASSOCIATED ASCIGEROUS STAGE.

A NEW SPECIES OF PHYLLOSTICTA AND ITS ASSOCIATED ASCIGEROUS STAGE.