Under the Microscope root rot

Armillaria luteobubalina is a fungal very low rate but has been shown to phytopathogen endemic to . JL Smith-White * † occur regularly enough to initiate new First described by Podger et al 1, this clonal infections. BA Summerell * species affects a wide range of plants in Once penetration of the host has been horticultural and native environments of * Royal Botanic Gardens & Domain Trust Mrs Macquaries Rd achieved, Armillaria characteristically temperate regions within Australia, Sydney, NSW 2000 releases a group of cell degrading colonising root and trunk tissue. This † Department of Land enzymes that include hemicellulases and colonisation causes tissue necrosis and Water and Crop Sciences cellulases. These enzymes breakdown Faculty of Agriculture ultimately death of the host, giving it the the cellulase fibrils and hemicellulase disease name of . Food and Natural Resources University of Sydney, NSW 2006 matrix of the primary and secondary plant This disease has brought about cell walls. It is this process that causes the considerable economic loss to majority of damage to the host. Although the majority of disease spread is horticultural, forestry and amenity Colonisation was thought to be restricted thought to be through root contact, plantings. To date, control options are to the base of the plants; however, recent studies that have investigated mating allele limited, with removal of the infected findings by the authors have shown that combinations 2, 6 [authors’ unpublished material as the only proven successful colonisation as high as 5 metres up the data] have shown that approximately half management procedure. stems of certain species can occur of all clones at a given site will be related [authors’ unpublished data]. Armillaria sp. through the process of sexual endemic to Australia recombination. This suggests that Identification basidiospore dispersal and sexual For many years the identification of Prior to the 1970s, all Armillaria species recombination have an impact on the Armillaria root rot and Armillaria species were identified as A. mellea, the major epidemiology of A. luteobubalina. relied upon macro- and micro-scopic species found throughout Europe. variations in basidiome morphology, During 1970-80 Kile and colleagues 1-3 Disease development and characteristics in culture and mating studies. identified five species based on host response morphological and biological species Armillaria fruiting bodies are generally concepts: A. luteobubalina, A.. hinnulea, The major disease symptoms include produced annually from the end of A. fumosa, A. novae-zelandiae and A. rotten water-soaked roots, leaf wilting, Autumn to early Winter. This can be a pallidula. dieback, trunk-splitting and collar rot. simple and time efficient technique for The development of these symptoms is identification when the fruiting bodies are Only A. luteobubalina, the most highly dependent upon environmental produced. However, not all field isolates abundant species found within Australia, conditions and the host species. Some of Armillaria produce fruiting bodies is considered to be a of plants show no or few symptoms for every year and mis-diagnosis can be significant concern. This species can be many years until the combination of made. generally characterised by its extensive infection and significant stress yellow/brown fruiting body, thick yellow causes them to die within a number of Identification to species level from the annulus and ivory white . days. root material is extremely difficult and Rhizomorph production is sparse under unreliable due to the similarity across all There are three forms of disease most field environments 4 but abundant in species. Isolation of the can be transmission exhibited by Armillaria: the culture. Specimens have been found in a extremely difficult and may require production of rhizomorphs; contact wide range of environments, such as incubation for extensive periods of time. between infected and non-infected roots; coastal plains, dry schlerophyll In recent years, however, identification and the dispersal of basidiospores. As forests and blue gum high forests, but are techniques for Armillaria have rhizomorphs are not produced to any generally restricted to temperate regions broadened to encompass molecular significant degree by A. luteobubalina, of the Australian coastline and ranges 5. characteristics. A molecular technique for this is not a significant form of the identification of A. luteobubalina has Sites of high disease prevalence are transmission and so contact between been developed recently based on a PCR- usually composed of more than one clone infected and non-infected roots is the RFLP technique 7. (genetically different individuals) with main method of clonal expansion. In individual clones relatively small comparison, the dispersal of Control compared to those found in some of the basidiospores as a form of disease The are no effective means of control of northern hemisphere species 2. transmission is considered to occur at a this disease other than by removing all the

MICROBIOLOGY AUSTRALIA • JULY 2003 31 Under the Microscope infected material from soil. This may Transactions of the British Mycological Society 5. Kile GA. Identification of genotypes and the involve extensive excavation of root 1978; 71, 77-87. clonal development of Armillaria systems and may involve large machinery 2. Kile GA & Watling R. Armillaria species from luteobubalina in eucalypt forests. Australian southeastern Australia. Transactions of the Journal of Botany 1983; 31, 657-671. and considerable expense. No chemical British Mycological Society 1983; 81, 129-140. control is currently available; however, 3. Kile GA & Watling R. Identification and 6. Dunne CP, Glen M, Tommerup IC, Shearer BL & biological control options using other occurrence of Australian Armillaria spp. Hardy GES. Sequence variation in the rDNA ITS fungi are being investigated. Host including Armillaria pallidula sp.nov. and of Australian Armillaria species and intra- comparative studies between them and non- resistance is poorly understood but may specific variation of A. luteobubalina. Australian tropical and Indian Armillaria. offer some hope for control of the disease. Transactions of the British Mycological Society Australasian 2002; 31, 241-251. 1988; 91, 305-316. 7. Smith-White JL, Summerell BA, Gunn LV, Rinzin C, References 4. Shearer BL & Tippett JT. Distribution and impact Porter C & Burgess LW. Molecular detection and 1. Podger FD, Kile GA, Watling R & Fryer J. Spread of in the and effects of Armillaria luteobubalina sp. nov. marginata forest of south-. differentiation of Australian Armillaria species. in an Australian plantation. Australian Journal of Botany 1988; 36, 433-446. Australasian Plant Pathology 2002; 31, 75-79. Mycorrhizas and revegetation

Much of Australia has extremely addition, the local community expect the Peter McGee impoverished soil. Phosphate is site to be returned to a state resembling particularly deficient. The major difficulty Greg Pattinson the original vegetation when the site is in revegetating these soils after severe Anne-Laure Markovina returned. Results from initial plantings disturbance is that plant survival and School of Biological Sciences A12 from seed by the operators indicate that a 1 growth is unpredictable . University of Sydney, NSW 2006 very limited number of plant species Mycorrhizas are associations between soil- would grow. None of these formed AM. A borne fungi and the roots of plants. Of We set out to determine whether AM may much more effective approach to particular interest are the arbuscular play a role in revegetation of highly revegetation was required. disturbed sites. We were particularly mycorrhiza (AM) whose fungi form an We germinated seed of four plant species interested in whether inoculation with internal colony in the roots of some 70% of collected from the site. Seedlings were mycorrhizal fungi was necessary, whether all plant species. In AM, the fungi function either inoculated with AM fungi obtained the inoculated fungi would establish in as extensions of the root system, enabling from a similar soil, or fertilised to a similar the plant to increase uptake of non-labile disturbed soils, and whether we could size. We transplanted the seedlings to the minerals, especially phosphorus (P), from provide a long-term benefit by site and followed survival and growth of soil. The fungus gains its organic energy inoculation. the plants, and survival and spread of the from the plant, and can only be maintained The experimental site was a waste disposal AM fungi over 20 months. in the presence of living roots. area south of Sydney. The region is Only fertilised or mycorrhizal seedlings Experiments in the laboratory over many characterised by open vegetation typical survived to the transplanting stage, years have demonstrated the importance of Hawkesbury Sandstone. In broad indicating that, unless fertiliser was of mycorrhizas to plant growth 2. terms, the operators at the site move the continually applied to the soils, However, as most Australian plants are bedrock and soil to one side, the waste is mycorrhizal fungi were essential for the adapted to impoverished soils, their deposited and compacted, and then the long-term maintenance of vegetation at growth response to mycorrhizas is crushed sandstone mixed with soil is the site. At the field site, fertilised and difficult to detect in the laboratory. placed over the waste (Figure 1). In mycorrhizal seedlings had a similar rate of Use of fertiliser improves survival and Figure 1. View of the experimental site following capping of the waste. growth of most seedlings. If seedlings of Australian plants store minerals in their tissues, then we may be able to transplant fertilised seedlings in revegetation programmes, and expect them to thrive, albeit at slow rates of growth. However, much of Australia is also subject to regular fire. Seedlings are burnt back to the ground, releasing minerals to smoke and ash. Thus fertiliser may simply enable survival to the first fire unless the seedlings first become colonised by appropriate mycorrhizal fungi.

32 MICROBIOLOGY AUSTRALIA • JULY 2003