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Title:   Author  item
                                            Baumgartner, Kendraitem
                                            RIZZO, DAVID - PLANT PATHOLOGY UC DAVIS
  Submitted to: American Journal of Enology and Viticulture
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/1/2006
                                    Publication  Date: 12/1/2006
                                    Citation: Baumgartner, K., Rizzo, D.M. 2006. RELATIVE RESISTANCE OF GRAPEVINE ROOTSTOCKS TO ARMILLARIA ROOT DISEASE. American Journal of Enology and Viticulture. 57:408-414.Interpretive Summary: Grapevine rootstocks were screened for resistance to infection by Armillaria mellea, the pathogen that causes Armillaria root disease of grapevine.  Our first objective was to determine which factors hasten colonization of grapevines by the pathogen, in order to hasten our inoculation technique.  We found that wounding the root bark and underlying conducting tissue did not significantly increase infection rate and that fine roots (' 5 mm-diam) were not susceptible to infection.  The only factor we found accelerated infection by the pathogen was plant age; younger plants were infected faster than older plants.  Based on these findings, we modified the inoculation technique and screened eight grapevine rootstocks in pots in the greenhouse.  After 2 yrs, replicate plants of each rootstock were examined for signs of the pathogen and infection was confirmed by attempting to culture the pathogen from inoculated root collars.  Freedom had the lowest frequency of infection (7%) and was the most resistant rootstock.  O39-16, 5C, Riparia Gloire, and 3309C had the highest frequencies of infection with 63%, 73%, 79%, and 85%, respectively.  St. George, Ramsey, and 110R had intermediate frequencies of infection.  Our findings suggest that Freedom and, to a lesser extent, St. George, Ramsey, and 110R will be useful components of an integrated management strategy for Armillaria root disease.  Resistant rootstocks may decrease the rate of colonization of grapevines in A. mellea-infested vineyards, thereby reducing yield losses from Armillaria root disease.
                                Technical Abstract: Grapevine rootstocks were screened for resistance to infection by Armillaria mellea, the pathogen that causes Armillaria root disease.  Our first objective was to determine which factors hasten colonization of grapevines by A. mellea, in order to accelerate our inoculation technique.  We found that wounding the root collar bark and vascular cambium did not significantly increase infection rate (p = 1.0), that young vines were infected significantly faster than older vines (p = 0.03), and that fine roots (' 5 mm-diam) were not susceptible to infection.  Based on these findings, we modified the inoculation technique and inoculated dormant rootings of eight rootstocks in the greenhouse.  After 2 yrs, their root collars were examined for the presence of mycelial fans of A. mellea and infection was confirmed by culture.  Freedom had the lowest frequency of infection (7%) and was the most resistant rootstock (p = 0.0016).  O39-16, 5C, Riparia Gloire, and 3309C had the highest frequencies of infection with 63%, 73%, 79%, and 85%, respectively.  St. George, Ramsey, and 110R had intermediate frequencies of infection.  Our findings suggest that Freedom and, to a lesser extent, St. George, Ramsey, and 110R will be useful components of an integrated management strategy for Armillaria root disease.  Resistant rootstocks may decrease the rate of colonization of grapevines in A. mellea-infested vineyards, thereby reducing yield losses from Armillaria root disease.


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