PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
RESISTANT, TOLERANT VARIETIES
LEGISLATION
WHAT DOES
RESISTANCE/
TOLERANCE
MEAN?
ENVIRONMENTAL ACTS, PESTICIDE ACTS, ETC may regulate their use, eg
GM crops must be approved for release.
Prescribed growing of resistant varieties which do not require pesticide
sprays in buffer zones close to urban settlements or in pest-free quarantine areas.
Phylloxera, a root-and foliage-feeding aphid, is one of the world’s most
devastating pests of grapevines is slowly spreading in Australia and can only be
controlled through the use of resistant root stock and quarantine measures.
A FEW DEFINITIONS
The use of resistant and tolerant plant varieties is an increasingly important
solution to insect and other plant problems.
Host resistance/tolerance may be based on chemicals present in the host
plant, colour or morphological features, such as thorny and hairy surfaces that
make it difficult for insects to feed on foliage, etc.
– Traditional cross breeding. The parent plant is crossed (hybridized) with
a cultivated or wild species which has the desired resistant genes.
– Genetic engineering. Genes for resistance are transferred into susceptible crop
varieties, thereby reducing the time required to develop new resistant varieties.
– Some pests may adapt to resistant or tolerant species and if large plantings
are planned, some non-resistant or non-tolerant varieties should be included.
Immune
Resistant
Tolerant
Cannot be infected by a given pest or pathogen.
Possessing qualities that hinder the development of a
given pest, pathogen; may be affected little or not at all.
The ability of a plant to sustain the effects of a pest or
disease without dying or suffering serious injury or crop
loss. Even slightly tolerant varieties can be useful.
Acceptable levels of damage on these varieties
(thresholds of damage) can be defined before sprays
need to be applied, eg green mirids on cotton.
SOME EXAMPLES
UNLIMITED RANGE OF TOLERANCE AND RESISTANCE IN NATURE
Some species of eucalypts are more or less tolerant to pests such as gumtree
scale, lerp and Christmas beetle attack. But provenances and individual trees
within each eucalypt provenance may differ in their tolerance to Christmas beetles.
Genetic engineering is increasingly being used to modify crops so they have
some resistance or tolerance to certain insect pests and other plant problems
reducing pesticide use, eg
– Probably the best known is Ingard cotton (Bt cotton) which has been
genetically modified to produce its own insecticides, ie to produce protein from
Bt which is toxic to cotton bollworms (Helicoverpa spp.), the major caterpillar
pests of cotton, but not toxic to beneficial or other organisms.
– Peas have been genetically engineered to have resistance to the pea weevil
(Bruchus pisorum) which is a major pest of peas.
Christmas beetles favour certain eucalypts.
Corn earworm, cotton bollworm is a major
pest of sweetcorn, cotton, ornamentals.
Pea weevil severely
damages field peas.
Fig. 36. Resistant/tolerant hosts is the only long term solution to these pests.
Insects and allied pests - Integrated pest management 45