College of Agricultural, Human, and Natural Resource Sciences

Department of Plant Pathology

Successful MS Final Exam

Congratulations to Eric Christianson on passing his MS thesis defense exam on July 7th. The title of his thesis was “Screening carrot germplasm for resistance to Xanthomonas hortorum pv. carotae”. Eric’s thesis committee consisted of Lindsey du Toit (thesis committee chair, Department of Plant Pathology), Steve Jones (co-chair, Department of Crop & Soil Sciences), Scot Hulbert (Chair of the Department of Plant Pathology), and Irwin Goldman (carrot breeder and chair of the Department of Horticulture at the University of Wisconsin-Madison).

Eric also presented part of his thesis at the APS Pacific Division meeting in Bozeman, MT on July 9-11, where he took second place in the student paper competition.

Eric Christianson thesis defense 7-7-14 cropped

(l to r) Steve Jones, Scot Hulbert, Irwin Goldman, Eric Christianson, Lindsey du Toit

For his thesis, Eric screened 66 Plant Introduction (PI) lines from the carrot (Daucus carota) germplasm collection of the United States Department of Agriculture (USDA) National Plant Germplasm System, along with two inbred lines from the USDA Agricultural Research Service, 17 commercial cultivars, and 16 wild carrot relatives for resistance to the bacterial blight pathogen, Xanthomonas hortorum pv. carotae in greenhouse trials. This pathogen is readily seedborne and endemic in the Pacific Northwest, where >50% of the world supply of carrot seed is grown. Genetic resistance is limited in commercial cultivars, and there has been little public research on screening for resistance. Eric identified 8 putative resistant PI lines and 5 highly susceptible PI lines from a 2012 screening, which were evaluated again in 2013 along with cultivars, inbreds, and wild relatives of carrot collected from various places in the world. PIs 418967, 432905, and 432906 were the most resistant based on pathogen population recovered from the foliage, and were more resistant than all the commercial carrot cultivars screened. There was little resistance displayed by the carrot wild relatives. Resistance from the selected PIs will be integrated into commercially-acceptable carrot inbreds for release to public and private carrot breeding programs.  Additionally, assays of 25 seed/PI revealed the presence of Alternaria radicina (which causes black rot of carrot) on 56.1% of the seed lots, A. carotiincultae on 1.5% of the seed lots, A. dauci (which causes Alternaria leaf blight) on 51.5% of the lots, and A. petroselini (a pathogen of parsley, not carrot) on 1.5% of the PI seed lots from the USDA NPGS collection, highlighting the need for treatment of carrot PI seed to avoid disseminating these pathogens with the seed.

Eric is pursuing a career in vegetable breeding, particularly with biennial vegetables such as carrot and onion.

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