First Report of a Rust Disease on Ohia Caused by Puccinia psidii in Hawaii

Abstract

Several species of Metrosideros (Myrtaceae), referred to as ohia in Hawaii, are endemic trees that comprise as much as 80% of the native Hawaiian forests. For centuries, these trees have provided niches for many indigenous and endangered plants and animals and are treasured by Hawaiians for their beauty and role in folklore and legends. During April 2005, a cultivated ohia plant was diagnosed by the Agricultural Diagnostic Service Center at the University of Hawaii at Manoa as infected by a rust fungus. Rust pustules containing abundant urediniospores were observed on leaves, stems, and sepals, causing discolored spots and severe deformity of young leaves and growing tips. By July 2005, a similar rust disease was observed on other plants in the family Myrtaceae; namely Syzygium jambos (L.) Alston, Eugenia koolauensis Degener, E. reinwardtiana (Blume) DC, and Psidium guajava L. Microscopic examination of the uredinia and urediniospores showed that the rust was morphologically similar to Puccinia psidii, which is reported as the guava or eucalyptus rust in Florida and Central and South America (1,2). To confirm the identity of this fungus, DNA was extracted from urediniospores of two isolates collected from ohia plants, and their nuclear ribosomal internal transcribed spacer (ITS) was amplified with two universal primers, ITS4 and ITS5 (3). Sequences of the ITS region of these isolates from ohia were identical to the P. psidii isolates provided by A. Alfenas in Brazil and M. Rayachhetry in Florida. Koch's postulate of the isolates, obtained from ohia, was performed using 1 × 108 spores/ml of urediniospores suspension in distilled water. The suspension was sprayed onto 6-month-old ohia seedlings. These inoculated seedlings were placed in clear plastic chambers maintained at 100% relative humidity and 22°C with a combination of 10-h fluorescent light period and a 14-h dark period. After 48 h of incubation, the seedlings were removed from the chambers and transferred to a greenhouse where the ambient temperature ranged from 20 to 24°C. Rust pustules appeared after 1 to 2 weeks of incubation. Symptoms first appeared as tiny, bright yellow, powdery eruptions that developed into circular, uredinial pustules on the stem and foliage. These pustules later expanded, coalesced, and became necrotic, spreading over the entire leaf and stem surfaces, and then leaves and stems were deformed and tip dieback ensued. These symptoms were the same as those observed on the naturally infected cultivated ohia plant mentioned above. P. psidii is reported to be native to South and Central America that later spread to some Myrtaceous plants in the Caribbean countries (1). It has a very wide host range within the family Myrtaceae (2). To our knowledge, this is the first report of P. psidii in Hawaii. This rust disease may pose a formidable threat to Myrtaceous species that make up the native Hawaiian forests and are grown as ornamental plants or for the production of wood chips. References: (1) T. A. Coutinho et al. Plant Dis. 82:819. 1998. (2) M. B. Rayachhetry et al. Biol. Control 22:38. 2001. (3) T. J. White et al. Page 315 in: PCR Protocols. M. A. Innis et al., eds. 1990.

Indigenous Biosecurity: Māori Responses to Kauri Dieback and Myrtle Rust in Aotearoa New Zealand

“…It is indigenous to South and Central America and the Caribbean (Teulon et al 2015) but has spread to many other regions, including New Guinea and Australia, where it is threatening the extinction of several plant species of significance to Aboriginal Australians (Robinson et al 2016). It was discovered in Hawai'i in 2005 and has since devastated the `Ōhi'a tree which is an important species for native Hawaiians (Uchida et al 2006). Since its arrival in Australia in 2010, its host range has doubled to over 346 known Myrtle Rust hosts globally, and at least nine native New Zealand Myrtaceae species that are cultivated in Australia have been confirmed as being infected (Teulon et al 2015).…”

A unique genotype of the rust pathogen, Puccinia psidii, on Myrtaceae in South Africa

“…The fungus has subsequently been reported Unique Pucinnia psidii genotype in South Africa 3 from North America (Marlatt and Kimbrough 1979) and Hawaii (Uchida et al 2006), China (Zhuang and Wei 2011), Japan (Kawanishi et al 2009), Australia (Carnegie et al 2010), Africa (Roux et al 2013), New Caledonia (Giblin 2013;Machado et al 2015) and Indonesia (McTaggart et al 2015). All of these reports, outside Brazil, were attributed to a single genoptype of P. psidii (Machado et al 2015), dubbed the pandemic genotype .…”

Impacts of the invasive fungusAustropuccinia psidii(myrtle rust) on three Australian Myrtaceae species of coastal swamp woodland

“…The fungus has a high dispersal capacity with spores moved by wind or attached to insects and animals, including humans (Uchida et al 2006). The fungus was accidentally introduced to Victoria (Agriculture Victoria 2016) and more recently been detected in Tasmania (Biosecurity Tasmania 2015) and the Northern Territory (DPIF 2015).…”

“…As the pathogen attacks apical buds, tree growth is reduced with greater branching resulting in a shrub-like habit (Booth et al 2000;Glen et al 2007), while infection of leaves and juvenile stems can result in distorted growth (Coutinho et al 1998;Glen et al 2007). Symptoms can range from purple flecks in resistant plants, through to the characteristic yellow sori with urediniospores on the leaves and stems in susceptible species, to defoliation and even death in the most vulnerable species (Rayachhetry et al 2001;Uchida et al 2006;Carnegie et al 2016).…”