Submitted to: Walnut Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/30/2010
Publication Date: 1/1/2011
Publication URL: http://walnutresearch.ucdavis.edu/2010/2010_239.pdf
Citation: Hackett, W., Leslie, C., Grant, J., Lampinen, B., Mcgranahan, G., Anderson, K., Beede, B., Buchner, R., Caprile, J., Debuse, C., Hasey, J., Manterola, N., Robinson, R., Kluepfel, D.A., Browne, G.T., Mckenry, M. 2011. Clonal Propagation of walnut rootstock genotypes for genetic improvement 2010. Walnut Research Conference. 2010:65-82. Interpretive Summary:
Technical Abstract: The soilborne bacterium Agrobacterium tumefaciens is the causal agent of crown gall disease of walnut. Large tumors located near the crown of the tree are hallmark symptoms induced by the bacterial pathogen. Untreated tumors can have an adverse effect on tree health resulting in reduced nut yield and tree vigor. At present, crown gall disease is managed using surgical removal the gall and infected tissues or complete excavation of the diseased tree. This is a costly and time consuming endeavor especially if a large number of trees are infected. The presence of Agrobacterium spp. in all walnut growing regions surveyed indicates the likelihood of a crown gall outbreak in any area or county is possible. This makes improved host resistance in commercial walnut rootstock genotypes a requirement for better crown gall management. Wild species are often the best source for identifying durable resistance to pests and pathogens. The walnut germplasm collection at the National Clonal Germplasm Repository (NCGR), USDA-ARS in Davis, CA contains a large and diverse array of black walnuts and butternuts adapted to California conditions including J. hindsii, J. nigra, J. microcarpa, J. ailantifolia, J. major, and additional wingnut selections belonging to the genus Pterocarya. Members of the collection from multiple species have been screened to characterize their resistance to Agrobacterium tumefaciens within the NCGR collection. Juglans species exhibiting increased tolerance to infection by A. tumefaciens strain EC1 have been identified. Further characterization of these novel sources of Agrobacterium resistance will be exploited in the ongoing U.C. Davis Walnut root stock breeding program to develop suitable rootstocks with improved resistance to crown gall.