First Report of Dolabra nepheliae Associated with Corky Bark Disease of Langsat in Hawaii
Authors: Keith L. M. , Matsumoto T. K. , McQuate G. T. 
Published: January 2013

In January 2011, branch samples were collected from langsat (Lansium domesticum Corr.), a fruit from Southeast Asia with an expanding niche market in Hawaii, exhibiting corky bark symptoms similar to that found on rambutan (Nephelium lappaceum) and litchi (Litchi chinensis) (3). The orchard, located along the Hamakua Coast of Hawaii Island, had 5- to 10-year-old trees, all with corky bark symptoms. As the trees matured, the cankers increased in size and covered the branches and racemes, often resulting in little to no fruit production. Scattered along the infected bark tissue were elongated, black ascomata present in the cracks. Ascomata were removed from the cracks using a scalpel blade, placed at the edge of a water agar petri dish and gently rolled along the agar surface to remove bark tissue and other debris. Individual ascomata were placed in 10-μl drops of 10% sodium hypochlorite on fresh water agar for 20 s, removed, and placed on potato dextrose agar petri dishes amended with 25 μg/ml streptomycin. The isolates were kept at 24°C under continuous fluorescent lighting. After 9 days, black pycnidia were present, which produced smooth, hyaline, linear to curved, filiform conidia, 4 to 6 septate (mostly 6), 31.8 to 70.1 × 2.0 to 2.8 μm. The morphological descriptions and measurements were similar to those reported for Dolabra nepheliae (3). The nucleotide sequence of the internal transcribed spacer (ITS) region including ITS1, 5.8S, and ITS2 intergenic spacers was determined for strain P11-1-1and a BLAST analysis of the sequence (GenBank Accession No. JX566449) revealed 99% similarity (586/587 bp) with the sequence of D. nepheliae strain BPI 882442 on N. lappaceum from Honduras. Based on morphology and ITS sequencing, the fungus associated with the cankers was identified as the same causal agent reported on rambutan and pulasan (N. mutabile) from Malaysia (1), and later reported on rambutan and litchi in Hawaii and Puerto Rico (3). Upon closer observations of the diseased samples, sections of corky bark contained at least two larval insects. The beetles were identified as Corticeus sp. (Coleoptera: Tenebrionidae) and Araecerus sp. (Coleoptera: Anthribidae) by the USDA-ARS Systematic Entomology Laboratory (Beltsville, MD). A corky bark disease on the trunk and larger limbs of mature langsat trees in Florida was thought to be caused by Cephalosporium sp. with larvae (Lepidoptera: Tineidae) feeding on the diseased tissue (2). It is not known the extent to which either of the beetle species is associated with L. domesticum in Hawaii or if they play a role in the bark disorder. To our knowledge, this is the first report of Dolabra nepheliae being found on langsat in Hawaii. Effective management practices should be established to avoid potential production losses or spreading the disease to alternative hosts.

References: (1) C. Booth and W. P. Ting. Trans. Brit. Mycol. Soc. 47:235, 1964. (2) J. Morton. Langsat. In: Fruits of Warm Climates, p. 201-203. Julia F. Morton, Miami, FL, 1987. (3) A. Y. Rossman et al. Plant Dis. 91:1685, 2007.