AbstractsBiology & Animal Science

Role of Aphanomyces trifolii and nutrition in root disease of Trifolium subterraneum

by O'Rourke, Tiernan A.

Institution: University of Western Australia
Degree: PhD
Year: 2009
Keywords: Subterranean clover; Subterranean clover; Subterranean clover; Subterranean clover; Root disease; A. trifolli; Necrotrophic pathogens
Record ID: 1031866
Full text PDF: http://repository.uwa.edu.au:80/R/?func=dbin-jump-full&object_id=13282&local_base=GEN01-INS01


[Truncated abstract] Subterranean clover (Trifolium subterraneum) is the most important pasture legume across southern Australia, including Western Australia where some 6 million had been sown by the mid 1970s (Gladstone 1975). Decline in subterranean clover pastures manifests as a decrease in the composition of desirable species, especially the legumes, and increased weed species. It was first recognized as a problem in Western Australia during the 1960s. Root disease is the main contributing factor to pasture decline. Despite its significant impact on pasture productivity, a detailed survey of root disease on subterranean clover has not been carried out in south-west Western Australia for at least two decades. While the impact of root disease has been examined on seedlings, it has not been examined on mature subterranean clover. The management of root diseases in subterranean clover based pastures is still a major challenge, as there are no completely resistant cultivars to the spectrum of pathogens that cause root disease. Nutrient applications have been recommended for optimal subterranean clover pasture growth throughout the south-west of Western Australia, but the relationship between mineral nutrition and root disease has not been previously examined. To date, the importance of Aphanomyces as a causal agent of root disease of subterranean clover has not been examined in Western Australia. For this reason, the aims of my PhD were to: First, conduct a field survey of tap and lateral root disease on mature subterranean clover in pastures in the south-west of Western Australia. Secondly, determine if nutrient applications can be used to manage tap and lateral root disease of subterranean clover in south-west Western Australia. Thirdly, isolate, describe and determine the pathogenicity and role of the novel Aphanomyces sp. causing root disease on subterranean clover in south-west Western Australia. Fourthly, screen subterranean clover germplasm to identify useful resistance to the previously undescribed Aphanomyces sp. The field survey determined that severe root disease was widespread on mature subterranean clover across south-west Western Australia. The high level of root disease observed will significantly adversely affect pasture growth rates in spring and appropriate management strategies need to be developed to accommodate this late season component of root disease in subterranean clover. The nutrient application studies determined for the first time that subterranean clover root disease can be effectively managed with the application of a ‘complete fertiliser’. The application of a ‘complete fertiliser’ (in the form of a Hoaglands solution) decreased the severity of tap root disease by an average of 47% and lateral root disease by 35% in experiments conducted in soil cores collected from three field sites at Denbarker, Denmark and Mt Barker in south-west Western Australia. The greatest reductions in root disease severity were for Denbarker, where the severity of tap root disease decreased a massive 76%…