Articles
CROWN GALL INCIDENCE AND SEVERITY: SEEDLING WALNUT ROOTSTOCK VERSUS CLONALLY PROPAGATED ROOTSTOCK
Article number
1050_41
Pages
305 – 308
Language
English
Abstract
Seedling hybrid Paradox (Juglans hindsii × Juglans regia) has been the rootstock of choice for English walnut farming in California because of its vigor and greater tolerance to wet soil conditions.
Unfortunately, Paradox is susceptible to crown gall, a disease caused by the soil-borne bacterium Agrobacterium tumefaciens. Micropropagation is a potential technology to manage crown gall incidence.
In California, micropropagated own-rooted English walnut trees became commercially available in 1999 and were planted as a strategy to manage blackline disease.
Micropropagated clonal Paradox rootstocks also became available at about the same time.
In 2000, a walnut rootstock experiment was planted in Stanislaus County, California comparing seven treatments; six rootstocks grafted to the Vina cultivar in 2001 and one own-rooted Vina that was not grafted.
The design was a randomized complete block with eight trees per plot and four replicates.
In 2007 and in 2012, field surveys were conducted to determine crown gall incidence.
Crown gall incidence was determined visually by scoring the presence or absence of tumors at the ground level.
In 2007, both seedling rootstocks had significantly more crown gall compared to the clonal Paradox Vlach and own-rooted English trees.
In 2012, both seedling rootstocks exhibited significantly more crown gall compared to all the clonally propagated rootstocks Vlach had a 16% increase in the number of galled trees over the 5-year period.
In 2012 crown gall severity also was assessed.
Galled trees of seedling Paradox averaged 51.5% circumference affected by tumors compared to 29.6% for Vlach and 17.3% for own-rooted English trees.
Micropropagated clonal rootstocks exhibited significantly lower crown gall ratings than seedling rootstocks at 7 and 12 years post-plant.
Unfortunately, Paradox is susceptible to crown gall, a disease caused by the soil-borne bacterium Agrobacterium tumefaciens. Micropropagation is a potential technology to manage crown gall incidence.
In California, micropropagated own-rooted English walnut trees became commercially available in 1999 and were planted as a strategy to manage blackline disease.
Micropropagated clonal Paradox rootstocks also became available at about the same time.
In 2000, a walnut rootstock experiment was planted in Stanislaus County, California comparing seven treatments; six rootstocks grafted to the Vina cultivar in 2001 and one own-rooted Vina that was not grafted.
The design was a randomized complete block with eight trees per plot and four replicates.
In 2007 and in 2012, field surveys were conducted to determine crown gall incidence.
Crown gall incidence was determined visually by scoring the presence or absence of tumors at the ground level.
In 2007, both seedling rootstocks had significantly more crown gall compared to the clonal Paradox Vlach and own-rooted English trees.
In 2012, both seedling rootstocks exhibited significantly more crown gall compared to all the clonally propagated rootstocks Vlach had a 16% increase in the number of galled trees over the 5-year period.
In 2012 crown gall severity also was assessed.
Galled trees of seedling Paradox averaged 51.5% circumference affected by tumors compared to 29.6% for Vlach and 17.3% for own-rooted English trees.
Micropropagated clonal rootstocks exhibited significantly lower crown gall ratings than seedling rootstocks at 7 and 12 years post-plant.
Publication
Authors
J.K. Hasey, D.A. Kluepfel, K.K. Anderson
Keywords
Juglans hindsii × Juglans regia, clonal Paradox, Paradox, own-rooted English walnut, Agrobacterium tumefaciens, micropropagated
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