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Title:   Author  item
                                            Kluepfel, Danielitem
                                            McClean, Aliitem
                                            Aradhya, Mallikarjunaitem
                                            Moersfelder, Jeffitem
                                            DULL, ADRIANE - US Department Of Agriculture (USDA)item
                                            MARSDEN, CHRISTY - US Department Of Agriculture (USDA)item
                                            HACKETT, WES - University Of California
  Submitted to: Walnut Research Conference
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 12/15/2011
                                    Publication  Date: 1/15/2012
                                    Citation: Kluepfel, D.A., Mcclean, A.E., Aradhya, M.K., Moersfelder, J.W., Dull, A., Marsden, C., Hackett, W. 2012. Evaluation of wild juglans species for crown gall resistance. Walnut Research Conference. 313-317.Interpretive Summary:
                                Technical Abstract: A. tumefaciens is a soil-borne Gram-negative bacterium which causes crown gall on many dicotyledonous plant species including walnut. Crown gall symptoms on walnut are characterized by large tumors located near the crown of the tree but can occur near wounds caused by bleeding cuts or at the graft union on younger trees.
After symptoms develop, management of the disease is limited to "surgical" removal of gall tissue from the infected plant or excavation of the entire tree. Both methods are expensive, labor intensive and time consuming. The ubiquitous soil-borne presence of A. tumefaciens in all CA walnut growing regions surveyed to date, coupled with the fact that the number one root stock, Paradox, is highly susceptible to crown gall, highlights the importance of locating a source of crown gall resistance for use in commercial walnut production.
Several wild walnut species including Juglans microcarpa, Juglans cathayensis, Juglans ailantifolia, and Pterocarya species were examined in an attempt to identify a source of crown gall resistance. Select Juglans microcarpa seedlings have been consistently identified as the Juglans species with increased tolerance to crown gall disease. A selected cross was made between Serr (pollen source) and a J. microcarpa mother tree 31.7 (identified as producing crown gall tolerant seedlings) to begin large-scale genetic analysis of walnut resistance to crown gall. Additional Juglans and Pterocarya seedlings were prepped for additional disease screening in the early spring to locate additional sources of reistance.


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