Botanic Gardens Trust, Sydney, Australia

Plant Pathology and Mycology research 2009-2010

Dr Edward Liew - Manager Plant Pathology
Lucas Shuttleworth - PhD Candidate

On-going research in the plant pathology and mycology section includes documenting and describing foliar diseases of members of the Proteaceae and Myrtaceae, describing new species of the fungal genus Fusarium, understanding the biogeography and evolution of soil inhabiting and endophytic species of Fusarium, studying movement and distribution of economically significant Fusarium pathogens and investigating disease management strategies for a range of diseases incited by the water mould Phytophthora, including root rot of Wollemi Pine. The research group has also been investigating the aetiology and management of a variety of ornamental and horticultural diseases.

Research Highlight

One of the plant pathology PhD students, Lucas Shuttleworth, has been investigating the aetiology and biology of Chestnut Rot in south eastern Australia. Chestnut rot is a significant problem facing the Australian chestnut industry, causing projected losses between 17- 30 $M annually. The disease manifests in brown lesions occurring on the endosperm and embryo of the chestnut, often not visible externally, presenting a challenge for growers and consumers alike.

There has been considerable confusion surrounding the identity of the Chestnut Rot pathogen. In Australia, the pathogen was previously identified as the ascomycetous fungus, Phomopsis castanea Sacc (Höhn) (anamorph) / Diaporthe castaneti Nitschke (teleomorph). More recently the Chestnut Rot pathogen was reclassified informally as Gnomonia pascoe sp. nov. Smith and Ogilvy. In his investigation based on morphological examination and phylogenetic analysis of representative isolates collected from various farms in Victoria and New South Wales, Lucas came to the conclusion that the pathogen belonged to yet another genus, describing it as a novel taxon, Gnomoniopsis smithogilvyi sp. nov.

The teleomorph of the pathogen was observed to survive as a saprophyte growing on decaying burrs on the orchard floor, which could serve as a reservoir of primary inoculum (ascospores) during summer when the trees are flowering. Lucas conducted an on-farm experiment and confirmed the presence of ascospores in the air with highest spore capture between 7-9 am and 8-10 pm, indicating climatic factors such as relative humidity and temperature affected ascospore release.

Lucasí studies also elucidated the abundance of the pathogen, as endophytes, found within living tissues of the chestnut tree, including (from highest to lowest frequency) the female flowers, male flowers, developing burrs, leaves, stems, and developing chestnut shells. This has important implications on disease management for farmers.

Mature chestnuts
Mature chestnuts in burr on chestnut tree

Healthy nut
Healthy chestnut

Rotten nut
Chestnut Rot symptoms

Perithecia 
The perithecia (sexual fruiting bodies) of the pathogen found on the inside surface of decaying burrs

Asci
Asci containing ascospores produced within perithecia. Ascospores are ejected from perithecia and infect chestnut flowers

Photos: Lucas Shuttleworth