prevents the virus from
efficiently making copies of
itself thus reducing damage
and yield loss. This approach
has been used to create
Asgrow's commercial viralresistant
yellow crookneck
squash variety. Tomatoes also
Concepts and Definitions:
Disease resistance genes form
the basis of a natural genetic
defense system in which a
specific plant gene interacts
with a specific gene from the
disease-causing organism in
what is called a “gene-forgene
recognition system”. It
is somewhat analogous to a
lock and key mechanism in
which the one component
must fit precisely with the
other component if it is to
work completely and
effectively. Disease
resistance genes are called
plant R or resistance genes
which can recognize a
complementary or “matching”
gene in the invading
pathogen. Avirulence
genes are the genes in the
disease-causing organism
(fungal, viral, bacterial,
nematode) with which the
disease resistance genes
“recognize” and with which
have been engineered with
the coat protein gene from
CMV (see photo, this page)
and are currently being fieldtested.
One difficulty with
the CP approach is that it is
often not broad-spectrum
protection and is specific for a
particular strain of virus.
Other strategies to protect
plants against viruses are
being examined that may lead
to broader spectrum
protection. These approaches
include ones based
on natural resistance genes
that may protect not only
against viral diseases but
possibly against other pests
and diseases also