Biology Reference
In-Depth Information
more than a couple of years, and that sudden
outbreaks of crown gall on land not previously
growing susceptible crops are due to irrigation
water bringing in viable bacteria from other
infected orchards. The addition of lime to the
soil may encourage crown gall, for bacteria do
not live in an acid medium. The period of greatest
activity is during the warm months.
Control
For home gardens rigid exclusion of all
suspected planting stock is the very best control.
Do not accept from your nurseryman blackberries,
raspberries, roses, or fruit trees showing suspicious
bumps. If you have had previous trouble, choose
a different location for new, healthy plants. Be
careful not to wound stems in cultivating.
For nurserymen, sanitary propagating prac-
tices are a must. Stock should be healthy.
Grafting knives should be sterilized by frequent
dipping in 10 % Chlorox solution, 1 ounce in 2
gallons of water, or in denatured alcohol. If nurs-
ery soil is infested, 2 years' growth of cowpeas,
oats, or crotalaria between crops will minimize
crown gall.
Fruit and nut growers can perhaps plant less
susceptible varieties, although fruit that is resis-
tant in one locality may be diseased in another.
American grape varieties are considered more
resistant than European. Apples may be better
on mahaleb root-stock, nut trees on black walnut
understock. Budding rather than grafting reduces
the chance of infection.
Painting galls with a solution of Elgetol-
methanol has given control of crown gall on
peaches and almonds in California. One part
Elgetol (sodium dinitrocresol) is shaken with 4
parts synthetic wood alcohol and applied with
a brush, covering the surface of the gall and
extending 1/2 inch to 1 inch beyond the margin
into healthy bark.
Fig. 1
Crown Gall on Rose
commonly at the graft union, but sometimes on
roots or aerial parts. On euonymus, galls are
formed anywhere along the vine. This is primar-
ily a disease of the parenchyma, starting with
a rapid proliferation of cells in the meristematic
tissue and the formation of more or less convo-
luted soft or hard overgrowths or tumors. The
close analogy of the unorganized cell growth of
plant galls to wild cell proliferation in human
cancer has intrigued scientists for many years.
In some fashion bacteria provide stimulus for
this overdevelopment, but similar galls have
been produced on plants experimentally by
injecting a virus or growth-promoting substances.
Entrance of bacteria into plants for natural
infection is through wounds. In nurseries and
orchards nematodes, the plow, the disc, or the
hoe may be responsible; on the propagating
bench grafting tools are indicted. Many claims
have been made for the longevity of crown gall
bacteria in soil, but it now seems to be established
that they do not live in the absence of host plants
Coryneform Group Mycobacteriaceae
Clavibacter
Slender, straight to slightly curved rods, with
irregularly stained segments or granules, often
with pointed or club-shaped swellings at ends;
