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Modeling Pathogen DNA Content and Visual Disease Assessment in Seed Tubers to Inform Disease in Potato Progeny Root, Stolon, and Tubers

January 2015 , Volume 99 , Number  1
Pages  50 - 57

Robert S. Tegg and Ross Corkrey, Tasmanian Institute of Agriculture, University of Tasmania, New Town Research Laboratories, New Town 7008, Australia; Herdina Herdina and Alan C. McKay, South Australian Research Development Institute, Urrbrae, South Australia 5064, Australia; Nigel S. Crump, ViCSPA, Healesville, Victoria 3777, Australia; Rudolf F. de Boer and Tonya J. Wiechel, Department of Environment and Primary Industries, AgriBio Centre for AgriBiosciences; and Calum R. Wilson, Tasmanian Institute of Agriculture, University of Tasmania, New Town Research Laboratories, New Town 7008, Australia

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Accepted for publication 5 July 2014.

Measurement of pathogens on seed tubers is essential for informing likelihood of subsequent potato disease. Here we utilized quantitative PCR assessment of pathogen DNA and visual assessment of disease to measure seed tuber inoculum and used this to model development of disease in potato grown in pathogen-free soil. Analysis by recursive partitioning and modeling using receiver operating curves indicated both abundance of Rhizoctonia solani AG3 and Streptomyces scabies DNA, and disease symptoms associated with these pathogens on seed tubers could predict subsequent disease in progeny tubers and for R. solani, stolons. In contrast, abundance of Spongospora subterranea DNA and disease symptoms on seed tubers were not consistently associated with powdery scab in progeny tubers. The relationship between S. subterranea DNA and seed tuber symptoms on root galling was stronger. Symptomless seed tubers that carried high levels of S. subterranea DNA were also associated with greater root galling than those with low pathogen DNA levels. There was a modest association between root galling and powdery scab in progeny tubers. These results highlight the importance of using certified seed tubers, and demonstrate a statistical tool for measuring the impact of seed tuber-borne inoculum.

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