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Cambistat is a growth regulator that changes where a tree invests
energy. By disrupting key steps in the isoprenoid pathway it reduces
the amount of gibberellic acid produced and shoot
elongation decreases by 40-60% over three years across a wide
variety of species. Energy not invested as shoot growth may be directed
elsewhere, and it is known that isoprenoid pathway substrates that
are not allowed to become gibberellin are precursors to tree chemicals
that play roles in pathogen defense.
Morphological Changes
Regulating the growth of a tree causes changes in form and
appearance. Some of the more notable changes include increased leaf
thickness, increased leaf hairs, and thicker leaf cuticles. These
changes tend to improve water status of leaves, and may present
additional physical barriers to pathogen invasion. What follows
are brief updates of research that has tested how well growth regulation
may protect trees from various diseases.
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 Treated
trees produce thicker leaves |
untreated |
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| Increase
amount of trichome hairs in treated trees. |
untreated |
| Research and Photographs
courtesy of Qi, Knighten, and Dr.Bill Chaney of Purdue
University |
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Apple Scab in Crabapples
To date there have been inconsistent reports of symptom suppression
of apple scab on crabapples treated with Cambistat. In test plots
at the Morton Arboretum, Dr. Gary Watson observed growth regulation
caused significant decreases in scab on leaves of a susceptible variety,
but field observations by Rainbow in Minneapolis suggest a wide range
of responses are possible. Growth regulation does not appear to consistently
influence how well crabapples defend themselves against this pathogen. Ongoing research may provide a better explanation for this in 2004-2005. |
Example of inconsistent
effect of growth regulation on apple scab in Minneapolis.
(click images to view a magnified version) |
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| untreated |
treated |
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| untreated |
treated |
| Growth regulation has had
a strong effect on symptom expression of apple scab in
a trial at the Morton Arboretum – results have been seen
for two years. |
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