ARS | Publication request: The quest to identify disease resistance in the USDA-ARS Juglans germplasm collection

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2012
Publication Date: May 31, 2012
Repository URL: http://www.actahort.org/books/948/948_11.htm
Citation: Kluepfel, D.A., Aradhya, M.K., Browne, G.T., Mckenry, M.V., Leslie, C.A., Mcclean, A.E., Moersfelder, J.W., Velasco, D.M., Baumgartner, K. 2012. The quest to identify disease resistance in the USDA-ARS Juglans germplasm collection. Acta Horticulturae. 948:105-111.

Technical Abstract: Ninety-nine percent of the U.S. Persian walnut crop is produced in California, USA, where walnut trees are typically grown on the hybrid rootstock Paradox (Juglans hindsii x Juglans regia). However, despite their popularity and relative advantage, Paradox seedling rootstocks are susceptible to Agrobacterium tumefaciens (crown gall), root-lesion and root-knot nematodes, Armillaria mellea (Armillaria root disease) and Phytophthora spp. (Phytophthora root and crown rot). Each of these diseases can cause serious loss to the California walnut industry. Therefore, continued walnut rootstock improvement is needed to identify disease-resistant, commercially-acceptable rootstocks. Towards this end we are examining the Juglandaceae collection at the USDA-ARS National Clonal Germplasm Repository (NCGR) in Davis, CA (USA). This collection contains the largest assemblage of wild Juglans spp. in North America with >550 accessions of black walnut, Asian butternut, Persian walnut, and wingnut (Pterocarya). Our preliminary evaluations of this Juglans germplasm collection has revealed resistance to A. tumefaciens and Phytophthora spp. among the J. hindsii, J. major, J. microcarpa and Pterocarya accessions, and root-lesion nematode resistance in J. cathayensis. Preliminary evaluations of these initial findings provide a foundation for continued examination of Juglans wild relatives to identify novel genotypes, which may contain valuable genes for disease resistance and environmental adaptation.