Identification and Control of Cylindrocarpon Black Foot Disease in California

Black foot disease of grape, caused by Cylindrocarpon spp., became a problem in vineyard
establishment in California in the 1990s. Symptoms of the disease are sunken root lesions,
black vascular streaking, leaf scorch symptoms resembling water stress, vine stunting, and
death. Partial sequences of ribosomal DNA internal transcribed spacer, beta-tubulin gene and
mitochondrial small subunit ribosomal DNA, morphology, and pathogenicity were used to
describe Cylindrocarpon spp. isolated from grapevines infected with black foot disease.
Variation of sequences was unexpectedly high among Cylindrocarpon spp. strains. Indeed,
isolates belonged to two paraphyletic clades and both caused disease on grapevine. Eighteen
isolates formed a divergent monophyletic sister clade of the rest of the C. destructans
complex. These strains produced larger spores than others and a unique orange-dark brown
colony on 2%malt extract agar, which discriminated them from other grapevine isolates
found in this work. This study revealed the existence of a new species in the genus
Cylindrocarpon. Black foot disease in California appears to be a disease complex caused by
more than one species of Cylindrocarpon.
Control of Cylindrocarpon spp. by pre-plant fumigation with methyl bromide has been
successful on peach and plum, on nursery grapevines, and on strawberry. Nevertheless,
alternatives to methyl bromide are needed since it is a Class I ozone depleter which is
scheduled for use reduction in USA by 2005.
In the 1990s, black foot disease was particularly obvious in areas extensively replanted with
phylloxera-resistant rootstock. Because of the phylloxera epidemic, the AXR1 rootstock,
used almost exclusively for 20 years, has been replaced by other rootstock varieties. This
suggested that this new presence of Cylindrocarpon on grapevine could be a problem of
rootstock susceptibility. Our first year trial supported this hypothesis. AXR1 was among the
least susceptible rootstocks. Our last trial showed that SO4, Salt Creek and Rupestris were
highly susceptible. Scharzmann, 44-53, 110R and 5 C inoculated with the pathogen had a
higher but not significantly higher root rot index. Riparia, 039-16 and Freedom showed no
susceptibility to the disease. We are currently repeating the test of resistance of those
rootstocks to black foot disease.
In California, factors of stress were associated with disease damage in vineyards. As vine
age increases, susceptibility to the disease decreases. We considered that this could be a
replant disorder that is amenable to biocontrol using mycorrhizal fungi in both nurseries and
new or renovated vineyards. Our study showed that the root weight and percent of lesions in
mycorrhizal plants inoculated also inoculated with the pathogen were not significantly
different from the healthy control. Inoculating vines with the mycorrhizal fungus Glomus
intraradices before inoculation with the pathogen, resulted in very good control of the
disease.