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ISHS Acta Horticulturae 948: I International Symposium on Wild Relatives of Subtropical and Temperate Fruit and Nut Crops

THE QUEST TO IDENTIFY DISEASE RESISTANCE IN THE USDA-ARS JUGLANS GERMPLASM COLLECTION

Authors:   D.A. Kluepfel, M.K. Aradhya, G.T. Browne, M.V. McKenry, C.A. Leslie, A.E. McClean, J. Moersfelder, D. Velasco, K. Baumgartner
Keywords:   rootstocks, disease resistance, Juglans, walnut breeding, crown gall resistance, phytophthora resistance, nematode resistance
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 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.
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