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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/14/2008 Publication Date: 3/20/2008 Citation: Keith, L.M. 2008. First report of Pestalotiopsis virgatula on rambutan in Hawaii. Plant Disease 92(5):835. Interpretive Summary: Rambutan is a tropical fruit that is becoming more popular in niche markets in Hawaii. Diseased fruit is commonly observed in orchards in Hilo. The fungus causing dark brown to black spots on rambutan was identified by morphological and molecular methods. The fungus is described and Koch’s postulates were completed. This is the first report of Pestalotiopsis virgatula causing fruit spots on rambutan in Hawaii. Technical Abstract: Rambutan (Nephelium lappaceum) is a tropical, exotic fruit that has a rapidly expanding niche market in Hawaii. Diseased rambutan fruit was commonly observed in orchards in Hilo during January 2006. The disease appeared as dark brown to black spots on mature fruit and blackened areas at the base of spinterns of mature and immature fruits. Pieces of infected fruit were surface-sterilized for 2 min in 0.5% NaOCl, plated on potato dextrose agar, and incubated at 24 degrees C + 1 degree C for 7 days. The fungus growing on PDA was pale buff with sparse aerial mycelium and acervuli containing black, slimy spore masses. All isolates had 5-celled conidia. Apical and basal cells were hyaline, while the three median cells were olivaceous; the upper two were slightly darker than the lower one. Conidia were 20.3 x 6.8 'm. There were typically three apical appendages averaging 16.8 'm long. The average basal appendage was 3.8 'm long. The fungus was initially identified as Pestalotiopsis virgatula (Kleb.) Stey. based on conidial and cultural characteristics (1), and the identification was confirmed by molecular analysis of the 5.8S subunit and flanking internal transcribed spacers (ITS1 and ITS2) of rDNA amplified from DNA extracted from single-spore cultures using the ITS1/ITS4 primers (2,3) and sequenced (GenBank Accession No. EU047943). To confirm pathogenicity, mycelial plugs of the fungus were used as inoculum. Agar pieces, 3 mm in diameter, from 7-day old cultures were applied. Mature fruit from rambutan cv. R134 were rinsed with tap water, surface-sterilized with 0.5% NaOCl for 2 min, wounded with a needle head, inoculated in the laboratory and maintained in a moist chamber for 7 days. Lesions resembling symptoms that occurred in the field were observed on fruit after 7 days. No symptoms were observed on fruit inoculated with agar media. The fungus reisolated from diseased fruit was identical to the original isolates, confirming Koch’s postulates. The disease appears to be widespread in Hawaii and may have the potential to affect post-harvest fruit quality. Pestalotiopsis spp. have been reported on rambutan in Malaysia, Brunei and Australia (4). This is the first report of P. virgatula causing fruit spots on rambutan in Hawaii. |
