ABSTRACT
Pipturus albidus (Hook. & Arn.) A. Gray or mamaki is a flowering plant species in the Urticaceae (nettles) endemic to the Hawaiian Islands. Mamaki is a forest and agricultural commodity, as well as a traditional medicinal and fiber crop. In August 2013, leaf rust was observed in Kuristown, Hawaii, on 15 mamaki plants. Infected leaves had vein-delimited chlorotic spots on the adaxial surface and yellow to orange uredinia on the abaxial surface. Uredinia were scattered, minute, pulverulent, subepidermal, and dome-shaped with a central pore, consistent with Pucciniastrum. Urediniospores were 16 to 23 × 10 to 14 µm, echinulate, ellipsoid to pyriform, walls hyaline, 0.5 µm thick, contents pale yellow to bright yellow. No teliospores were observed. A voucher specimen was deposited in the U.S. National Fungus Collections (BPI 892695). The only species of Pucciniastrum previously known on Pipturus, Pucciniastrum pipturi Syd. [syn. Uredo pipturi (Syd.) Hirats. f.], has larger urediniospores, 26.5 to 40.0 × 19.5 to 27.5 µm, and is currently reported from Japan and the Philippines (3). The pathogen was identified as Pucciniastrum boehmeriae (Dietel) Syd. & P. Syd., which infects Boehmeria Jacq., also in the Urticaceae, and has urediniospores that are 18 to 27 × 13 to 18 µm and similar in shape (2). DNA was extracted from uredinial lesions and the nuclear ribosomal internal transcribed spacer (ITS2) region and the 5' end of large subunit (28S) rDNA were amplified and sequenced following the protocol of Aime (1). The resulting fragment (GenBank Accession No. KF711854) was 100% identical to authenticated and vouchered P. boehmeriae ITS2/28S rDNA sequences (AB221449 to AB221451 and AB221391 to AB221393) (4). Sequences from P. pipturi are not available for comparison, but host family, molecular, and morphological data support the identification of the rust as P. boehmeriae, which is found throughout eastern Asia. To our knowledge, this is the first report of P. boehmeriae on mamaki and the first report in Hawaii on any host. Plant health professionals and regulatory officials can utilize this information to establish survey methods and implement appropriate management practices for this rust disease. References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) N. Hiratsuka. Revision of Taxonomy of the Pucciniastreae. Kasai Publishing and Printing, Tokyo, 1958. (3) M. Kakishima and T. Kobayashi. Mycoscience 35:125, 1994. (4) Y.-M. Liang et al. Mycoscience 47:137, 2006.
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.
ABSTRACT
Rambutan (Nephelium lappaceum L.) is a tropical fruit grown in Hawaii for the exotic fruit market. Fruit rot was observed periodically during 1998 and 1999 from two islands, Hawaii and Kauai, and severe fruit rot was observed during 2000 in orchards in Kurtistown and Papaikou on Hawaii. Symptoms were characterized by brown-to-black, water-soaked lesions on the fruit surface that progressed to blackening and drying of the pericarp, which often split and exposed the aril (flesh). In certain cultivars, immature, small green fruits were totally mummified. Rambutan trees with high incidence of fruit rot also showed symptoms of branch dieback and leaf spot. Lasmenia sp. Speg. sensu Sutton, identified by Centraalbureau voor Schimmelcultures (Baarn, the Netherlands), was isolated from infected fruit and necrotic leaves. Also associated with some of the fruit rot and dieback symptoms were Gliocephalotrichum simplex (J.A. Meyer) B. Wiley & E. Simmons, and G. bulbilium J.J. Ellis & Hesseltine. G. simplex was isolated from infected fruit, and G. bulbilium was isolated from discolored vascular tissues and infected fruit. Identification of species of Gliocephalotrichum was based on characteristics of conidiophores, sterile hairs, and chlamydospores (1,4). Culture characteristics were distinctive on potato dextrose agar (PDA), where the mycelium of G. bulbilium was light orange (peach) without reverse color, while G. simplex was golden-brown to grayish-yellow with dark brown reverse color. Both species produced a fruity odor after 6 days on PDA. In pathogenicity tests, healthy, washed rambutan fruits were wounded, inoculated with 30 µl of sterile distilled water (SDW) or a fungus spore suspension (105 to 106 spores per ml), and incubated in humidity chambers at room temperature (22°C) under continuous fluorescent light. Lasmenia sp. (strain KN-F99-1), G. simplex (strain KN-F2000-1), and G. bulbilium (strains KN-F2001-1 and KN-F2001-2) produced fruit rot symptoms on inoculated fruit and were reisolated from fruit with typical symptoms, fulfilling Koch's postulates. Controls (inoculated with SDW) had lower incidence or developed less severe symptoms than the fungus treatments. Inoculation tests were conducted at least twice. To our knowledge, this is the first report of Lasmenia sp. in Hawaii and the first report of the genus Gliocephalotrichum on rambutan in Hawaii. These pathogens are potentially economically important to rambutan in Hawaii. G. bulbilium has been reported previously on decaying wood of guava (Psidium guajava L.) in Hawaii (2), and the fungus causes field and postharvest rots of rambutan fruit in Thailand (3). References: (1) J. J. Ellis and C. W. Hesseltine. Bull. Torrey Bot. Club 89:21, 1962. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (3) N. Visarathanonth and L. L. Ilag. Pages 51-57 in: Rambutan: Fruit Development, Postharvest Physiology and Marketing in ASEAN. ASEAN Food Handling Bureau, Kuala Lumpur, Malaysia, 1987. (4) B. J. Wiley and E. G. Simmons. Mycologia 63:575, 1971.
