Colletotrichum Species Associated with Japanese Plum (Prunus salicina) Anthracnose in South Korea.

A total of 24 Colletotrichum isolates were isolated from diseased Japanese plum (Prunus salicina) fruits showing chlorotic regions with whitish-brown sunken necrotic lesions and phylogenetic relationships among the collected Colletotrichum isolates were determined. A subset of 11 isolates was chosen for further taxonomic study based on morphology and molecular characteristics identified using the internal transcribed spacer (ITS) and beta-tubulin (TUB2) genes. Isolates in the C. acutatum complex were analyzed using partial sequencing of five gene regions (ITS, GAPDH, ACT, TUB2, and CHS), and C. gloeosporioides sensu lato (s.l.) isolates were analyzed using seven gene regions (ITS, TUB2, GAPDH, ACT, CAL, CHS-1, and ApMat). Morphological assessments in combination with phylogenetic analysis delineated four species of Colletotrichum including C. gloeosporioides sensu stricto (s.s.), C. nymphaeae, C. foriniae, and C. siamense; these data identify Colletotrichum fioriniae and C. siamense two new species associated with plum anthracnose in South Korea. Finally, the pathogenicity of these four species in the development of plum anthracnose in South Korea was confirmed by inoculations of plum fruit.

Molecular and Morphological Characterization of Colletotrichum Species in the Colletotrichum gloeosporioides Complex Associated with Persimmon Anthracnose in South Korea.

Anthracnose is a major disease of persimmon in the pre- and postharvest phase. Several species of Colletotrichum (Colletotrichum gloeosporioides, C. acutatum, and C. horii) have been reported as causal agents of persimmon anthracnose in South Korea. In this study, a collection of 50 isolates associated with persimmon anthracnose were collected from Sangju (n = 25) and Cheongdo-gun (n = 25), South Korea. The morphological characteristics of all 50 Colletotrichum isolates were similar, and it was difficult to identify the isolates to the species level. A subsample of eight isolates was characterized phylogenetically to ascertain species. BLAST search and phylogenetic analysis of the internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and actin (ACT) genes revealed two species: C. horii as well as a previously unreported persimmon anthracnose causal agent C. siamense. C. siamense isolates were confirmed again by phylogenetic analysis of the ITS, ACT, GAPDH, calmodulin, and Apn2-Mat1-2 intergenic spacer partial mating type genes. Koch's postulates for C. horii and C. siamense were fulfilled, confirming the pathogenicity of the two species in persimmon fruit. Morphological characteristics (colony morphology and size and shape of conidia and appressoria) from two representative isolates support results of the phylogenetic analysis and match those of previous descriptions of C. horii and C. siamense.

Occurrence of Brown Blight Caused by Waitea circinata var. zeae on Cool Season Turfgrass in Korea.

In 2010, disease symptoms, including necrotic lesions on stems and leaves with circular yellow-brown or irregular brown color patches, were observed on cool-season turfgrass at golf courses (OHCC) and the Daegu University research farm in Gyeongbuk, Korea. We isolated the causal agent and identified it as Waitea circinata var. zeae by morphological characterization and molecular analysis. To the best of our knowledge, this is the first report of brown patch caused by W. circinata var. zeae on cool-season turfgrass in Korea.

Isolation and Identification of Antifungal Compounds from Bacillus subtilis C9 Inhibiting the Growth of Plant Pathogenic Fungi.

Antagonistic microorganisms against Rhizoctonia solani were isolated and their antifungal activities were investigated. Two hundred sixteen bacterial isolates were isolated from various soil samples and 19 isolates were found to antagonize the selected plant pathogenic fungi with varying degrees. Among them, isolate C9 was selected as an antagonistic microorganism with potential for use in further studies. Treatment with the selected isolate C9 resulted in significantly reduced incidence of stem-segment colonization by R. solani AG2-2(IV) in Zoysia grass and enhanced growth of grass. Through its biochemical, physiological, and 16S rDNA characteristics, the selected bacterium was identified as Bacillus subtilis subsp. subtilis. Mannitol (1%) and soytone (1%) were found to be the best carbon and nitrogen sources, respectively, for use in antibiotic production. An antibiotic compound, designated as DG4, was separated and purified from ethyl acetate extract of the culture broth of isolate C9. On the basis of spectral data, including proton nuclear magneric resonance ((1)H NMR), carbon nuclear magneric resonance ((13)C NMR), and mass analyses, its chemical structure was established as a stereoisomer of acetylbutanediol. Application of the ethyl acetate extract of isolate C9 to several plant pathogens resulted in dose-dependent inhibition. Treatment with the purified compound (an isomer of acetylbuanediol) resulted in significantly inhibited growth of tested pathogens. The cell free culture supernatant of isolate C9 showed a chitinase effect on chitin medium. Results from the present study demonstrated the significant potential of the purified compound from isolate C9 for use as a biocontrol agent as well as a plant growth promoter with the ability to trigger induced systemic resistance of plants.

Isolation, Identification and Optimal Culture Conditions of Streptomyces albidoflavus C247 Producing Antifungal Agents against Rhizoctonia solani AG2-2.

Streptomyces albidoflavus C247 was isolated from the soil of the Gyeongsan golf course in Korea. Physiological, biochemical and 16S rDNA gene sequence analysis strongly suggested that the isolate belonged to Streptomyces albidoflavus. Preliminary screening revealed that the isolate was active against fungi and bacteria. Self-directing optimization was employed to determine the best combination of parameters such as carbon and nitrogen source, pH and temperature. Nutritional and culture conditions for the production of antibiotics by this organism under shake-flask conditions were also optimized. Maltose (5%) and soytone (5%) were found to be the best carbon and nitrogen sources for the production of antibiotics by S. albidoflavus C247. Additionally, 62.89% mycelial growth inhibition was achieved when the organism was cultured at 30℃ and pH 6.5. Ethyl acetate (EtOAc) was the best extraction solvent for the isolation of the antibiotics, and 100 µg/ml of EtOAc extract was found to inhibit 60.27% of the mycelial growth of Rhizoctonia solani AG2-2(IV) when the poison plate diffusion method was conducted.