ABSTRACT
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 ß-tubulin gene was determined for strain Vr1 and a BLAST analysis of the ß-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.
ABSTRACT
Edible ginger is a popular spice crop that is grown in Hawaii primarily for the fresh market, and as such, rhizome quality is of paramount importance. In our studies, a Gram-negative, facultative anaerobic, rod-shaped bacterium was consistently isolated from decayed as well as symptomless ginger rhizomes. The bacterium was identified as Enterobacter cloacae by biochemical assays and 16S rDNA sequence analysis. Rot symptoms, which usually occurred in the central cylinder of the rhizome, were characterized by yellowish-brown to brown discolored tissue and firm to spongy texture. In inoculation experiments, ginger strains of E. cloacae produced basal stem and root rot, with foliar chlorosis and necrosis in tissue-cultured ginger plantlets, and discolored and spongy tissue in mature ginger rhizome slices and whole segments. In other hosts, ginger strains of E. cloacae caused internal yellowing of ripe papaya fruit and internal rot of onion bulbs. All strains that caused symptoms in inoculated plants were reisolated and identified as E. cloacae. Our studies suggest that E. cloacae can exist as an endophyte of ginger rhizomes, and under conditions that are favorable for bacterial growth, or host susceptibility, including maturity of tissues, rhizome rot may occur. Rhizome quality may be impacted by the presence of E. cloacae under conditions such as high temperature, high relative humidity, and low oxygen atmosphere that may affect the development of decay, and such conditions should be avoided during post-harvest handling and storage. The association of E. cloacae with a rhizome rot of ginger is a new finding.
