Agriculture Reference
In-Depth Information
showing infected leaves are brittle and readily break. The
wood is pitted and has a yellow to orange staining due to
gum impregnation. In severely affected trees, numerous
fine pits give the wood of small branches a honeycomb
appearance.
Mandarin stem pitting strains of this virus are exotic
to Australia and are a significant risk to Queensland's
large mandarin industry. If stem pitting symptoms like
those described above are found on any citrus except
grapefruit outside of Queensland, or on mandarins,
they should be reported and investigated by a plant
pathologist.
Importance
All popular grapefruit cultivars, including Marsh and
especially the red grapefruits, are susceptible to the
grapefruit stem pitting strains of
Citrus tristeza virus
and
the disease develops irrespective of the rootstock,
although is often worse in trees on rough lemon. All
Fig 6.47 Stem pitting in grapefruit.
Citrus tristeza virus
causes stem
pitting and grooving in wood, which can only be seen when the bark
is removed.
Fig 6.48 Stem pitting in orange. Severe pitting of young branches from
Washington navel infected by the orange stem-pitting strain can be
seen when the bark is removed.
Fig 6.46 Scaly butt (
Citrus exocortis viroid
). Bark cracking and scaling
occurs below the bud union.
