Location: Tropical Crops and Germplasm ResearchTitle: First report of Colletotrichum fructicola and C. queenslandicum causing fruit rot of rambutan (Nephelium lappaceum L.)
|Serrato-diaz, Luz M. - University Of Puerto Rico|
|Latoni-brailowski, E.i. - University Of Puerto Rico|
|Rivera-vargas, L.i. - University Of Puerto Rico|
|Bayman, Paul - University Of Puerto Rico|
|French-monar, R.d. - University Of Puerto Rico|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2017
Publication Date: 2/20/2017
Citation: Serrato-Diaz, L., Latoni-Brailowski, E., Rivera-Vargas, L., Goenaga, R.J., Bayman, P., French-Monar, R. 2017. First report of Colletotrichum fructicola and C. queenslandicum causing fruit rot of rambutan (Nephelium lappaceum L.). Phytopathology. Available: http://dx.doi.org/10.1094/PDIS-11-16-1557-PDN.
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, two fungi causing fruit rot were 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: In rambutan production, fruit rot is the main pre- and post-harvest disease of concern. In a 2008-2013 fruit disease survey, fruit rot was observed in eight orchards in Puerto Rico. Infected fruit were collected and 1 mm2 tissue sections were surface disinfested with 70% ethanol followed by 0.5% sodium hypochlorite, rinsed with sterile water (SW) and transferred to acidified potato dextrose agar (APDA). Two isolates of Colletotrichum fructicola (Cof) and two isolates of C. queenslandicum (Coq) were identified morphologically using taxonomic keys and molecularly, by PCR amplification of the ITS rDNA, fragments of ß-tubulin (BT), actin (ACT), chitin synthase (CHS), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes, sequencing, and BLASTn comparison with Colletotrichum spp. submitted to NCBI GenBank. In APDA, colonies of Cof were gray with aerial mycelial growth, acervuli were absent on culture, conidia (n=50) were 13.9 x 4.5 µm in length, one-celled, smooth walled, hyaline, cylindrical to oblong, and rounded at both ends. Apressoria were 4.5 x 6 µm diameter, perithecia were subglobose to ovoid, semi-immersed in APDA, and asci (n=20) were 56 x 11 µm in length, clavate, unitunicate, thin walled and contained 8 ascospores. Ascospores (n=50) were 11.4 x 4.3 µm in length, one-celled, hyaline, slightly curve and rounded at both ends. In APDA, colonies of Coq were gray with aerial mycelial growth and conidia (n=50) were 15 × 4.5 µm in length, cylindrical, hyaline, straight, and rounded at both ends. Appressoria were 7–10 µm diameter and perithecia were absent. The ITS sequences submitted to GenBank included accession Nos KT372375 and KT372376 (Cof) and KT372377 and KT372377 (Coq) to 78; for BT, accession Nos. KT372368 and KT372369 (Cof) and KT372367 and KT372370(Coq); for ACT, accession Nos. KT372384 and KT372385 (Cof) and KT372383 and KT372386 (Coq); for CHS , accession Nos. KT372379 and KT372382 (Cof) and KT372380 and KT372381 (Coq); and for GAPDH, accession Nos. KT372371 and KT372372 (Cof) and KT372373 and KT372374 (Coq). The sequences were >99% or identical with the ex-type specimens BPDI16 for Cof and ICMP 1778 for Coq for all genes used. Pathogenicity tests were conducted on five healthy superficially sterilized fruits per isolate. Both scalpel-wounded and unwounded fruit tissues were inoculated with 2 x 105 conidial suspensions from 8-day-old pure cultures grown in APDA. Untreated controls were inoculated with SW only. Fruits were kept in a humid chamber for 8 days at 25°C under 12 h of fluorescent light. The test was repeated once. Eight days after inoculation with Cof and Coq, all fruit turned brown, and acervuli were produced on spinterns (hairlike appendages). Rot of spinterns and exocarp (skin), water-soaked lesions on the fruit surface and aril (flesh) rot were observed. Untreated controls had no symptoms of fruit rot and no fungi were isolated from tissue. Both Cof and Coq were reisolated from their respective diseased tissue, fulfilling Koch's postulates. Colletotrichum gloeosporioides has been reported causing fruit rot of rambutan in Thailand and Sri Lanka. To our knowledge, this is the first report of C. fructicola and C. queenslandicum causing fruit rot of rambutan.