In Trinidad, pimento chili peppers (Capsicum annuum L.) are grown for large domestic and regional export markets. Production is intensive during the rainy season (June to December). In August 2010, pimento fruits with symptoms of fruit rot were collected from fields located in Tableland, Valencia, Aranguez-North and -South, and Macoya. Symptoms began as a discoloration and soft rot of the peduncle and calyx (green to brown then black); a tan, watery lesion (with irregular margins) developed and expanded rapidly from the calyx down the sides of the fruit with internal rot of the placenta. Excessive fruit drop was also common. Estimated yield loss was ~20 to 60% for each field. Symptoms were observed on green and red fruits. Fruits were surface disinfected (2 min in 70% ethanol, 2 min in 0.5% NaOCl, followed by three rinses with sterile distilled water) and then a 4-mm3 block of tissue was taken from the lesion edge and placed on water agar. After 7 days at 25 ± 1°C, a 4-mm3 block of agar that contained the advancing hyphal edge of each colony was transferred to selective fusarium agar (3) and incubated as previously described. Colonies were fast growing with white, fluffy, aerial mycelia; hyphae densely branched; polyphialides abundant; microconidia abundant, thin walled, hyaline, ovoid, aseptate or 1-celled, and 5.5 to 12.2 × 2.0 to 3.2 μm. Macroconidia were moderately curved to straight, hyaline, 3- to 4-celled, thick walled, and 20.5 to 35.0 × 3.5 to 5.0 μm. Molecular characterization was based on a two-loci approach. PCR amplification was carried out with universal primers (ITS4/5) and translation elongation factor primers (EF1/2) (2). Sequences of the ITS1-5.8S-ITS2 region of rDNA (GenBank Accession No. HQ333547) and partial EF-1α gene (GenBank Accession No. HQ333548) were compared to cognate sequences available in GenBank and the FUSARIUM-ID databases (2). Comparisons revealed 100% similarity to Fusarium proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg 1982. F. proliferatum (synonym Gibberella intermedia) is the anamorphic form of the G. fujikuroi complex that belongs to the Nectriaceae family (4). Pathogenicity tests were conducted by dispensing 10 μl of a prepared spore suspension (106 spores/ml) onto nonwounded and wounded sites of pimento fruits (landrace ‘Trinidad seasoning’, 10 fruits per isolate, 8 isolates). Negative controls were fruits inoculated with sterile distilled water. Inoculated fruits were kept at 25 ± 1°C in partially sealed plastic containers and monitored for the onset of symptoms for 7 days. The test was conducted twice. Lesions, similar to those recorded on field infected fruit, developed on inoculated fruits that were wounded and nonwounded, but not on water controls. The pathogen was reisolated from infected tissues, thereby fulfilling Koch's postulates. F. proliferatum is associated with disease of a number of economically important crops and ornamental plants worldwide (1). Fusarium fruit rot of pepper has been shown to significantly reduce marketable yield and shelf life of infected fruits. To our knowledge, this is the first report of Fusarium fruit rot of pimento chili peppers caused by F. proliferatum in Trinidad.
References: (1) J. Armengol et al. Eur. J. Plant Pathol. 112:123, 2005. (2) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (3) J. Leslie and B. Summerell. Page 1 in: The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (4) H. Nirenberg and K. O'Donnell. Mycologia 90:434, 1998.