No abstract

In June 2010, an internal fruit rot of sweet pepper (Capsicum annuum L.) fruit was found in a commercial greenhouse in Ilsan City, Korea. Disease incidence reached approximately 5% of 30 tons of harvested peppers. Affected fruits commonly did not show external symptoms. However, when the fruit was cut open, an internal rot and pinkish gray mycelium were observed on the seeds and the inner surface of fruit. Discolored soft patches, browning, and necrosis were observed on the outer surface of some fruits. Fragments (5 × 5 mm2) of the affected tissues were surface sterilized with 1% NaOCl for 30 s and then rinsed twice in sterile distilled water. The pieces were placed on water agar and incubated at 25°C for 4 to 6 days. Twenty-nine Fusarium isolates were obtained from 12 diseased fruits and maintained on synthetic low nutrient agar (SNA) at 10°C. The isolates were cultured on carnation leaf agar (CLA) and SNA at 23°C with 12 h of near-ultraviolet light per day for 14 days. Microconidia were abundant, borne in short, zig-zag chains or false heads, obovoid or clavate with a flattened base, and measured 4.3 to 7.1 × 2.2 to 3.3 μm. Macroconidia were sparse, thin walled, slender, straight to slightly curved, and measured 32 to 48 × 2.8 to 3.9 μm. Sporodochia were rare on CLA and chlamydospores were absent. The translation elongation factor 1-alpha (EF-1α) gene was amplified from four isolates (SPF01, SPF09, SPF16, and SPF22) by PCR assay using ef1 and ef2 primers (2), and the 700-bp amplification products were sequenced. The nucleotide sequences were deposited in GenBank (Accession Nos. JF411956 to JF411959). BLAST analysis showed 98% homology with the EF-1α sequence of Fusarium lactis NRRL25200 (GenBank Accession No. AF160272). All isolates were identified as F. lactis based on morphological and molecular characteristics (1). Pathogenicity tests of the four isolates were conducted by inoculating flowers on plants of the orange pepper cv. Orange Glory (3). A spore suspension was prepared by flooding 5-day-old cultures on potato dextrose agar with sterile distilled water. When the plants started to flower, each flower was inoculated by placing 20 μl of spore suspension (1 × 106 conidia/ml) on each flower. Four isolates of F. lactis were each inoculated onto three flowers on each of seven plants. Flowers from the same number of plants inoculated with sterile distilled water were used as the control treatment. Inoculated plants were kept in a greenhouse at 25°C by day and 20°C by night. Sixty days after inoculation, mature fruits were harvested and cut open to check for internal rot. Approximately 70% of inoculated fruits showed internal rot and pinkish gray mycelial growth on the inner surface of the fruits. No symptoms were observed on the control fruits. Fungal cultures resembling F. lactis were reisolated from inoculated fruits for all four isolates, fulfilling Koch's postulates. F. lactis has been reported on sweet pepper in the Netherlands and Canada (3). To our knowledge, this is the first report of internal fruit rot of sweet pepper caused by F. lactis in Korea. Although disease severity was low in this greenhouse, the economic impact on sweet pepper could be significant because the disease can reduce the quality, quantity, and market value of pepper fruits. References: (1) H. I. Nirenberg and K. O'Donnell. Mycologia 90:434, 1998. (2) K. O'Donnell et al. Proc. Natl. Acad. Sci. USA 95:2044, 1998. (3) J. Yang et al. Can. J. Plant Pathol. 31:47, 2009.

No abstract

In July 2010, flower rot of thread-leaf coreopsis (Coreopsis verticillata) was found in a garden in the Icheon City, Korea. The disease affected about 20 to 50% of a 100 m2 area. The disease was characterized by the appearance of pinkish mycelia on the stigmata and inflorescences of flowers. In some cases, flowers failed to bloom or turned brown before opening fully. Fragments (each 5 × 5 mm) of the symptomatic tissue were surface-sterilized with 1% NaOCl for 1 min, and then rinsed twice in sterilized distilled water. The tissue pieces were placed on water agar (WA) and incubated at 25°C for 4 to 6 days. Twenty-two isolates of Fusarium species were obtained from the diseased flowers. All isolates were identified as Fusarium succisae based on their morphological characteristics on carnation leaf agar (CLA) medium and DNA sequences of the translation elongation factor 1-alpha gene (1). Macroconidia and sporodochia were sparsely produced on CLA medium. Microconidia were abundant, borne in false heads, oval or allantoid and sometimes pyriform, and measured 4.2 to 13 × 2.2 to 5.4 μm. Chlamydospores were absent. The EF-1α gene was amplified from three isolates by PCR assay and the amplification products were sequenced (2). The nucleotide sequences obtained were deposited in GenBank with accession numbers KF514658, KF514659, and KF514660. BLASTn analysis showed 99% homology with the EF-1α sequence of F. succisae NRRL13613 (GenBank Accession No. AF160291). Pathogenicity tests were conducted with inoculation of flowers on Coreopsis verticillata. Spore suspension was prepared by flooding 7-day-old cultures on potato dextrose agar with sterilized 2% (w/v) sugar solution. When the plants started to have buds, the isolates were inoculated by placing one drop (20 μl) of spore suspension (1 × 106 spores ml−1) into the buds. Fifteen buds of the plants were arranged into three replications. The control was treated with sterilized 2% sugar solution. Inoculated plants were kept in a greenhouse at 25/20°C (12 h/12 h). Three weeks after inoculation, the symptoms were observed on buds with mycelial production. Control plants had no mycelia on buds. F. succisae was re-isolated from the inoculated flowers. To our knowledge, this is the first report of flower rot of thread-leaf coreopsis caused by F. succisae. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (2) K. O'Donnell et al. Proc. Nat. Acad. Sci. 95:2044, 1998.