'Genome to Paddock' Approach to Control Plant Disease

PLENARY 1 – DANIEL MCALPINE MEMORIAL LECTURE A ‘genome to paddock’ approach to control plant disease 1 Barbara Howlett 1. University of Melbourne, Melbounre, VIC, Australia Pathogenic fungi evolve in concert with their plant hosts to invade and overcome defence responses. A detailed knowledge of these processes is essential for successful disease management strategies. Blackleg caused by the fungus, Leptosphaeria maculans, is the major disease of canola worldwide. In this lecture I describe how field data, such as disease incidence and severity, coupled with information about the biology, molecular genetics and genomics of the blackleg fungus has been exploited to control this important disease. Field populations of Leptosphaeria maculans can evolve and overcome disease resistance bred into canola within three years of commercial release of a cultivar. The risk of breakdown of resistance can be determined by monitoring disease severity of canola cultivars and changes in virulence of fungal populations using high throughput molecular assays that are based on sequences of avirulence genes. Farmers can avoid a predicted epidemic by sowing canola cultivars with different resistance genes in subsequent years. This strategy has been exploited in Australia and has averted substantial yield losses due to disease. NOTES: CONCURRENT SESSION 1 – PEST AND PATHOGEN EVOLUTION AND DIVERSITY Linking molecules to morphology: fruit fly integrative taxonomy Mark K Schutze1, Matthew N Krosch1, Jane Royer2, Nicholas Woods3, Rodney Turner3, Melanie Bottrill3, Bill Woods4, Ian 4 1 1 5 Lacey , Jacinta McMahon , Francesca Strutt , Stephen L Cameron 1. Queensland University of Technology, Brisbane, QUEENSLAND, Australia 2. Queensland Department of Agriculture and Fisheries, Brisbane 3. Plant Health Australia, Canberra 4. Department of Agriculture and Food, Western Australia, Perth 5. Purdue University, West Lafayette, IN, USA Containing over 5,000 species, Tephritidae is a diverse fly family notorious for containing some of the world’s most destructive fruit pests, including the Mediterranean fruit fly, Oriental fruit fly, South American fruit fly, and Queensland fruit fly. As for most insects, traditional taxonomy has relied primarily on morphological characters to discriminate, define, and describe new species. This has failed to fully resolve some of the most important pest groups, especially those belonging to species complexes, leading to significant debates among the tephritid community. We argue that an integrative approach, correlating independent datasets to the same individual voucher specimens, represents the future of tephritid systematics, taxonomy, and diagnostics. This is particularly important for problematic groups of high biosecurity concern at higher risk of diagnostic confusion. The banana wilt fungus Fusarium oxysporum f .sp. cubense is even more diverse than previously anticipated 1 2 2 1 1 Diane Mostert , Wayne O'Neill , Suzy Perry , Lizel Mostert , Altus Viljoen 1. Plant Pathology, Stellenbosch University, Stellenbosch, Western Cape, South Africa 2. Biosecurity Queensland, Department of Agriculture and Fisheries , Brisbane, Queensland, Australia Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungus that causes Fusarium wilt of banana, a lethal disease that can result in devastating economic losses to banana production worldwide. The fungus, which originated in Asia, has a complex evolutionary history and taxonomic composition. It consists of three races, which are inadequately defined, and at least 24 vegetative compatibility groups (VCGs) that are separated by single to multiple sequence differences in the loci governing vegetative compatibility. VCG complexes are regularly formed between closely related groups. Extensive surveys of diseased banana plants in Asia resulted in the collection of pathogenic isolates of F. oxysporum that did not fit into any of the known Foc VCGs. These isolates were, therefore, properly characterized and assigned to new Foc VCGs. In the process, five multiple-member and eight single-member VCGs were assigned. Isolates previously assigned as new genotypes of Foc paired with the known VCGs 01221, 01222 and the VCG complex 0128/01220. Phylogenetic analyses indicated that the new Foc VCGs were closely related. The results obtained in this study suggest that more VCGs exist than originally anticipated, but that Foc is probably phylogenetically less diverse than reflected by the number of VCGs. NOTES: Sexual reproduction between Pyrenophora teres f. teres and Pyrenophora teres f. maculata is rare in barley field populations 1 2 3 3 3 1 1 Barsha Poudel , Mark McLean , Greg Platz , Ryan Fowler , Judy Mcilroy , Mark Sutherland , Anke Martin 1. University of Southern Queensland, Darling Heights, QLD, Australia 2. Agriculture Victoria , Horsham , VIC , Australia 3. Department of Agriculture and Fisheries, Hermitage Research Facility, Warwick, QLD , Australia Pyrenophora teres f. teres (Ptt) and P. teres f. maculata (Ptm) are foliar fungal pathogens of barley that respectively cause the net and spot forms of net blotch disease. Both pathogens co-exist on crop residue and reproduce sexually, potentially leading to hybridisation between them and the evolution of new virulent pathotypes that could overcome sources of resistance in current commercial barley varieties. To date only few studies have reported Ptt x Ptm hybrids in the field, but reproduction between Ptt and Ptm has been successfully induced under laboratory conditions. To investigate the incidence of sexual recombination between Ptt x Ptm in the field, susceptible barley varieties were infected with Ptt and Ptm isolates of opposite mating types at each of three sites to facilitate hybridisation. To test for Ptt x Ptm hybrids, 723 single conidia were isolated from infected leaf samples. Sequence-specific PCR markers amplified across DNA of each isolate indicated that none of the isolates were hybrids. Furthermore DArT (Diversity Array Technology) marker analysis indicated that recombination had taken place among Ptt and among Ptm isolates. These findings suggest that sexual hybridisation between Ptt x Ptm is rare and that there is preference for sexual recombination among isolates of the same form. Further investigations are needed to determine the conditions under which hybridisation may occur in the field. Host specificity in net form of net blotch of barley and barley grass caused by Pyrenophora teres fsp. teres 1 Celeste Linde 1. Australian National University, Canberra, ACT, Australia The interaction between hosts and pathogens and the severity of epidemics, depends heavily on the interactions between their genetic diversity, population size and transmission ability. Theory predicts that genetically diverse hosts will select for higher virulence and more diverse pathogens than hosts with low genetic diversity. Cultivated hosts typically have lower genetic diversity and thus small effective population sizes, but can potentially harbour large pathogen population sizes. On the other hand, hosts, such as weeds, which are genetically more diverse and thus have larger effective population sizes, usually harbour smaller pathogen population sizes. Large pathogen population sizes may lead to more opportunities for mutation and hence more diverse pathogens. Here we test the predictions that pathogen neutral genetic diversity will increase with large pathogen population sizes and host diversity. We assessed and compared the diversity of a fungal pathogen, Pyrenophora teres fsp. teres, on weedy barley grass (which have a large effective population size) and cultivated barley (low genetic diversity) using microsatellites and pathogenicity to assess the importance of weeds in the evolution of this pathogen. The findings indicated that the large barley acreage and low host diversity maintains higher pathogen neutral genetic diversity and has a higher effective population size. Thus, pathogen census population size is a better predictor for neutral genetic diversity than host diversity. However, the pathogen populations on the two hosts are distinct based on clustering of their microsatellite alleles and most importantly, do not show cross host pathogenicity. Thus, although weeds enhance the evolution of aggressiveness in some other pathosystems, here barley grass poses no threat to increased aggressiveness evolution of Pyrenophora teres fsp. teres on barley. NOTES: Genotyping of potato cyst nematode in Victoria, Australia, and comparison with populations from Europe and the Americas 1 1 1 1 2 2 Jacqueline Edwards , Arati Agarwal , John Wainer , Mark Blacket , Maggie D Tricka , Michael Renton 1. Agriculture Victoria, Bundoora, VIC, Australia 2. The University of Western Australia, Perth, WA, Australia Potato cyst nematodes (PCN) are damaging soil-borne quarantine pests of potatoes in many parts of the world. There are two recognised species, Globodera pallida and G. rostochiensis, of which only G. rostochiensis is present in Australia. PCN was first discovered in Australia in 1986 in a suburb of Perth, Western Australia, was subsequently eradicated and area freedom reinstated. In Victoria, PCN was first detected in February 1991 in Wandin, east of Melbourne. Since then it has been found in small pockets in Gembrook (1991), Emerald, Keysborough and Boneo (1992), Kooweerup/Cora Lynn (2003) and Thorpdale (2008), also east of Melbourne. Strict quarantine controls have been in place since each detection. In 2007, it was speculated that there may have

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