|HASEY, J.K. - University Of California - Cooperative Extension Service|
|LAMPINEN, B.D. - University Of California|
|ANDERSON, K.K. - University Of California - Cooperative Extension Service|
|GRANT, J.A. - University Of California - Cooperative Extension Service|
|CAPRILE, J.L. - University Of California - Cooperative Extension Service|
|BEEDE, R.H. - University Of California - Cooperative Extension Service|
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2010
Publication Date: 4/30/2010
Citation: Hasey, J., Lampinen, B., Anderson, K., Grant, J., Caprile, J., Beede, R., Kluepfel, D.A. 2010. CROWN GALL INCIDENCE: SEEDLING PARADOX WALNUT ROOTSTOCK VERSUS OWN-ROOTED ENGLISH WALNUT TREES. Acta Horticulturae. 861:453-455.
Technical Abstract: Seedling Paradox (Juglans hindsii x J. regia) has been the rootstock of choice for English walnut in California because of its vigor and greater tolerance of wet soil conditions. However, seedling Paradox rootstock is highly susceptible to crown gall, a disease caused by the soil-borne bacterium Agrobacterium tumefaciens. In regions where tree death from walnut blackline disease (cherry leafroll virus) is prevalent, seedling English rootstock is used to avoid the hypersensitive response at the graft union associated with Paradox. Own-rooted English trees have replaced seedling English in the nursery trade and are now often used in counties where walnut blackline disease is severe. Early observations revealed limited crown gall on own-rooted trees. In 2006-07, we conducted a statewide crown gall survey of own-rooted English walnut trees and Paradox rooted walnut trees at five rootstock research sites and 14 commercial orchards planted in 2003 or earlier. Crown gall incidence was determined by visual inspection, and rated as present or absent at the crown level. Every own-rooted tree at a site was compared to 100 English trees on Paradox growing near each site. Across the five research sites, seedling Paradox had significantly more crown gall (20.5 percent) compared to the own-rooted trees (0.95 percent). The commercial orchards had a similar pattern with seedling Paradox exhibiting 22.2 percent crown gall versus 0.3 percent in the own-rooted trees.