First Report of Calonectria Leaf Spot on Ohelo in Hawaii

Ohelo, Vaccinium reticulatum (Smith), is an endemic Hawaiian shrub, less than 1 m tall, which grows between 640 and 3,700 m elevation on disturbed volcanic sites on the islands of Maui and Hawaii (3). Ohelo berries are made into jams, jellies, and pie filling and are also a food source for the endemic nene goose, the state bird of Hawaii (3). In the summer of 2010, Ohelo berry plants grown in a greenhouse nursery located in Hilo, Hawaii, exhibited severe disease symptoms including leaf spots, stem lesions, and defoliation. The leaf spots appeared rapidly and were fairly severe. Subsequent field surveys of areas of naturally growing Ohelo within Hawaii Volcanoes National Park and along the roadside of Saddle Road were negative. An anamorphic state of Cylindrocladium was consistently isolated from the diseased portions of plants on potato dextrose agar (PDA). To determine the species, single-conidial isolates of the fungus were cultured for 14 days at 25°C under 12 h of light/dark conditions. Conidia were produced on penicillately branched condiophores having a stipe extension of 101.5 to 231.3 × 1.9 to 3.5 μm, terminating in a narrowly clavate vesicle, 2.4 to 3.5 μm. Conidia were hyaline, cylindrical, rounded at both ends, straight, three septate, and 58.6 to 77.77 × 4.29 to 5.72 μm. The nucleotide sequence of the partial β-tubulin gene was determined for strain Vr1 and a BLAST analysis of the β-tubulin sequence (GenBank Accession No. JX852715) revealed 99% similarity (337/341 bp) with the sequence of Calonectria pseudocolhounii strain CMW27213 (HQ285789) (1). Based on morphology and molecular sequencing, the fungus was identified as Calonectria irrespective of the teleomorphic stage in accordance with Lombard et al. (2). Koch's postulates were fulfilled by spray inoculating eight Ohelo seedlings and eight Ohelo variety N06-7 ('Kilauea') plants with a spore suspension (10⁵ conidia per ml) of one isolate of the pathogen obtained from 14-day-old single-spore colonies grown on PDA at 25°C. Following inoculation, all plants were maintained in plastic bags in a growth chamber at 25 ± 1°C and 90 to 95% relative humidity. Four plants were used as a control. After 5 to 7 days, foliar symptoms resembling those seen in the nursery were detected on inoculated plants; leaf drop was first observed after day 7. No symptoms were detected on the control plants. The Calonectria sp. was reisolated from the artificially infected tissues. To our knowledge, this is the first report of a Calonectria sp. causing disease on Ohelo berry in Hawaii. References: (1) S. F. Chen et al. Persoonia 26:1, 2011. (2) L. Lombard et al. Stud. Mycol. 66:1, 2010. (3) F. Zee et al. F&N-16, May 2011.