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.

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. References: (1) S. G. Bobev et al. Plant Dis. 86:1178, 2002. (2) F. M. Dai et al. Plant Dis. 90:1460, 2006. (3) U. Nilsson et al. Plant Dis. 89:1242, 2005. (4) A. Stensvand et al. Plant Dis. 85:558, 2001.

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 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. References: (1) D. L. Coyier et al. (Abstr.) Proc. Am. Phytopathol. Soc. 2:112, 1975. (2) S. Francis. Mol. Plant Pathol. 3:119, 2002.

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.