Location: Tropical Crops and Germplasm ResearchTitle: First report of Gliocephalotrichum bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico) Author
Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/17/2012
Publication Date: 8/1/2012
Citation: Serrato-Diaz, L.M., Latoni-Brailowsky, E.I., Rivera-Vargas, L.I., Goenaga, R.J., French-Monar, R.D. 2012. First report of Gliocephalotrichum bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico. Plant Disease. 96(8):1225. Interpretive Summary: Fungi are a very large and diverse group of organisms that cause serious diseases of crop and forest plants. Accurate knowledge of fungi is critical for controlling the diseases they cause. Rambutan is a tropical plant that produces delicious edible fruits. In this research, a fungus that causes fruit rot was discovered for the first time in Puerto Rico in rambutan trees. Knowledge of the identity of this plant pathogen is the first step to assess its impact on production of trees and to develop control measures, if necessary.
Technical Abstract: Worldwide, significant post-harvest disease losses of rambutan (Nephelium lappaceum L.) have been reported and several pathogens have been associated with fruit rot. Even though rambutan was introduced to Puerto Rico in 1927, it was not until 1998 that commercial farms were established in the western region of the island. During a survey conducted in 2011, fruit rot of rambutan was observed on trees at the USDA-ARS Tropical Agricultural Research Station in Mayaguez, P.R. Infected fruit sections (1mm2) were surface-sterilized, rinsed with sterile deionized-distilled water and transferred to acidified potato dextrose agar (APDA). Gliocephalotrichum bulbilium (Gb) and G. simplex (Gs), were identified using taxonomic keys and PCR amplification of the ITS1-5.8S-ITS2 region of the rDNA and ß-tubulin partial cds gene. In Corn Meal Agar (CMA), five isolates of Gb were initially light yellow but later turned light brown. Conidiophores contained sterile stipe extensions ranging from 120 to 150 µm long produced contiguous to the erect conidiogenous penicilli. Conidia were unicellular, smooth, oblong to elliptical, and 5.5 to 7.5 µm long by 2.0 to 2.5 µm wide. Bulbilloid aggregates were observed and averaged 70 µm in length. In CMA, five isolates of Gs were light brown to chestnut-brown. Conidiophores contained sterile stipe extensions ranging from 130 to 180 µm long and produced approximately 15-30 µm away from the conidiogenous penicilli. Conidia were unicellular, smooth, cylindrical to elliptical, and with slightly curved ends ranging of 6.5 to 8.5 µm long by 2.0 to 2.5 µm wide. Chlamydospores were unicellular, brown, smooth and thick-walled, averaging 35 µm in length. Pathogenicity tests were conducted on five detached fruits per each species. Five isolates of each Gliocephalotrichum species were inoculated on fruits using 5-mm mycelial disks of 8-day-old pure cultures grown in APDA. Untreated controls were inoculated with APDA disks only. Fruits were kept in a humid chamber for eight days and the test was repeated. Five days after inoculation (DAI), white mycelial growth for Gb and golden mycelial growth for Gs were observed on rambutan fruits. Eight DAI, fruit rot symptoms were observed on fruits inoculated with isolates of Gb and Gs. Infected fruits changed in color from red to brown, and, on average, mycelia of Gb and Gs covered 50 and 60% of the fruit, respectively. Conidiophores were observed on spintems (hair-like appendages). Both species were reisolated from diseased plant tissue, thus fulfilling Koch’s postulates. DNA sequences of the ITS region were obtained and submitted to NCBI GenBank for Gs (Accession Nos. JQ688045 and JQ688046) and Gb (Accession Nos. JQ688044 and JQ688047). DNA partial cds sequences of the ß-tubulin gene were submitted for Gs (Accession Nos. JQ688049 and JQ688050) and Gb (Accession Nos. JQ688048 and JQ688051). Both DNA regions had 99.9 to 100% sequence identity to other Gb and Gs reported in GenBank. These and other Gliocephalotrichum spp. are associated with rambutan fruit rot in Hawaii, Sri Lanka or Thailand. To our knowledge, this is the first report of G. bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico.