First report of Fusarium decemcellulare causing inflorescence wilt, vascular and flower necrosis of rambutan (Nephelium lappaceum), longan (Dimocarpus longan) and mango (Mangifera indica)

Authors: SERRATO-DIAZ, LUZ - University Of Puerto Rico; PEREZ-CUEVAS, MANUEL - Isa University; RIVERA-VARGAS, LYDIA - University Of Puerto Rico; Goenaga, Ricardo; FRENCH-MONAR, RONALD - Texas Agrilife Extension

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2015
Publication Date: 3/2/2015
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-09-14-0923-PDN.
Citation: Serrato-Diaz, L.M., Perez-Cuevas, M., Rivera-Vargas, L.I., Goenaga, R.J., French-Monar, R.D. 2015. First report of Fusarium decemcellulare causing inflorescence wilt, vascular and flower necrosis of rambutan (Nephelium lappaceum), longan (Dimocarpus longan) and mango (Mangifera indica). Plant Disease. Available: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-09-14-0923-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, longan and mango are tropical crops that produce delicious and nutritious fruits. In this research, a fungus that causes inflorescence wilt, flower and vascular necrosis was discovered for the first time in Puerto Rico in trees of these fruit crops. 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: Longan, mango and rambutan are very important fruit crops in Puerto Rico. During a disease survey in Puerto Rico conducted from 2008 to 2010, 50% of the inflorescences were affected with inflorescence wilt, flower and vascular necrosis at 70% of the fields of rambutan and longan at the USDA-ARS Research Farm in Isabela, three commercial orchards, and the Mango Germplasm Collection of the University of Puerto Rico’s Experiment Station in Juana Diaz. Diseased inflorescence from longan, mango and rambutan were disinfested with 70% ethanol, rinsed with sterile water (sw) and transferred to acidified potato dextrose agar (APDA). Four isolates of Fusarium decemcellulare Brick, Jahrb. Vereinig. Angew (Fd) were identified morphologically using taxonomic keys. On APDA, colonies of Fd were dark pink to reddish, producing yellow sporodochia and droplet exudates on culture media. Macroconidia (n=50) were hyaline, septate, fusiform, curved and extremely long, ranged from 60 to 76 µm long by 5 to 7 µm wide, with a rounded or blunt apical cell. Microconidia (n=50) were hyaline, oval and 0-1 septate produced in long chains, ranged from 7.5 a 12.9 µm long by 2.0 to 4.7 µm wide. Chlamydospores were absent. Globose perithecia were 120 to 200 µm in diameter with clavate, unitunicate asci measuring 60 to 70 µm long and 11 to 12 µm wide. Asci containing four to six hyaline, reniform, 3-septate ascospores, mesuring 15 to 20 µm long and 5 to 7 µm wide. For molecular identification, the ITS region of rDNA using ITS5-ITS4 primers, and a fragment of elongation factor 1-alpha (EF1-a) gene using EF1728F-EF1986R primers were amplified by PCR, sequenced and compared using BLASTN with Fusarium spp. submitted to the NCBI GenBank. Accession numbers of gene sequences were GU797410-11 and KF971882-83 for ITS region; and KF971884-87 for EF1-a. All sequences were 98 to 99 % identical to other sequences of Fd submitted to GenBank, accessions HM054153, HQ897815, HM054059, EU849670 – 71 and AB674295. For each fungal isolate, pathogenicity tests were conducted on six healthy non-detached inflorescences of rambutan, longan and mango using two trees of each fruit. Both needle-wounded and unwounded inflorescences were inoculated with conidial suspension (7.6 x 105 conidial/ml) from 15-day-old pure cultures of Fd grown in APDA. Inoculated inflorescences were kept in plastic bags for eight days under field conditions. Untreated controls were inoculated with sw only. The test was repeated twice. Eight days after inoculation, isolates of Fd caused flower necrosis and inflorescence wilt on rambutan and longan, respectively. On mango, isolates of Fd caused vascular necrosis and death of flowers along the rachis. No symptoms were observed in untreated controls. Fusarium decemcellulare was only re-isolated from diseased inflorescences, fulfilling Koch's postulates. Fusarium decemcellulare has been associated with branch cankers, galls and dieback of tropical trees such as avocado, cocoa, and mango. To our knowledge, this is the first time that Fd has been reported causing inflorescence wilt, vascular necrosis and flower necrosis in longan, rambutan, and mango.