mechanism of resistance in plant against insects
TRANSCRIPT
MECHANISM OF RESISTANCE IN PLANT
AGAINST ORIENTATION, FEEDING AND OVIPOSITION
OF INSECT
Arvind KumarH-13-1-D
KM. Painter classified mechanisms of resistance into 3 main categories
Antixenosis (Non preference)
Antixenosis is mechanism employed by the plant to deter or reduce
colonization by insects. Plants that exhibit antixenotic resistance should
have a reduced initial number of colonies early in the season.
Antibiosis
Antibiosis operates after the insect have colonized and have started
utilizing the plant.
Tolerance
Tolerance of the plant does not affect the rate of population increase of
the target pest but does raise the threshold level.
Antixenosis
ANTIXENOSIS TO OVIPOSITION
Resistance to oviposition may come from plant characteristics
that either fall to provide appropriate oviposition-inducing
stimuli or provide ovipositional inhibiting stimuli.
Oviposition preference is discussed on two bases of the plant’s
1. biophysical and
2. biochemical traits
BIOPHYSICAL FACTORS
Plant pubescence
Frego bract
Visual factors
PLANT PUBESCENCEInsects with piercing and sucking mouth parts are deterred from feeding on hairy plants or vascular bundles.
Breeding of hairy cottons in Africa and Asia to combat the Jassids Empoasca spp. constitutes the foremost host plant resistance (HPR).
Pargell et al., (1949) demonstrated that greater hairiness to both upland cotton (Gossypium hirsutum) and Egyptian cotton (G. barbadense) mm related to jassid resistance.
Soybean varieties with a dense hairiness of foliage can manifest both antixenosis to oviposition and feeding deterrence against leafhoppers, The simple trichomes deter oviposition and feeding by preventing; the insect’s ovipositor or proboscis from reaching the plant epidermis(Lee 1983)
Pubescent wheat cultivar Vel exhibits antixenosis to adults andlarvae of the Hessian fly Mayetiola destructor (Roberts et al., 1979).
FREGO BRACT
Other morphological features of plants, such as frego bract in cotton,
help reduce the number of eggs laid and subsequent damage by boll
weevils Anthonomus grandis (Jenkins and Parrot 1971).
In field experiments, frego-bract cotton showed 50% less damage
from oviposition than normal cottons did. The role of the frego bract
in reducing damage by the boll weevil appears to be due to some
adverse effect on insect behavior.
Frego bract is associated with hypersensitivity to the plant bugs
Lygus spp. and cotton fleahopper Pseudatomoscelis seriatus (Jenkins
et al 1973).
VISUAL FACTORS The colour and shape of plants remotely affect host selection
behaviour of phytophagous insects and have been associated with
some resistance.
Ex: Specific color-related resistance, For example, the red and glossy
nature of Cruciferae plants was a major factor conferring antixenosis
resistance against the cabbage aphid Brevicoryne brassicae (Singh
and Bills 1993).
Yellow colour is preferred by aphids
Green and blue green is preferred by cabbage butterfly
Dark green preferred by rice leaf folder
BIOCHEMICAL FACTORS Chemical cues are involved in all the three phases of host
selection behavior; orientation, oviposition and feeding. Many
factors play a role in the process of opposition by different
insects, but long-range orientation of many insects to their host
plants is known to be guided by volatile, compounds emanating
from plants. Volatile hydrocarbons and other secondary
compounds act as oviposition deterrents
Onion volatile diallyl disulfide is antagonistic to onion fly
Delia antiqua..
ANTIXENOSIS TO FEEDING
Insects respond to various feeding stimuli when selecting their host plants.
The absence of such stimuli and the presence of deterrent compounds
presumably contribute to antixeniosis types of resistance. The plant surface
is embedded with physical and chemical factors responsible for antixenosis
to feeding insects (Southwood 1986).
number of phytophagous insect species shows that before feeding on a
plant they make some land of sensory exploration of the plant surface as a
prelude to biting. The leaf surface acts as the crucial interface between the
insect's battery of chemoreceptors and the plant (Southwood 1986
ANTIXENOSIS TO FEEDING
Nonglandular trichomes
Glandular trichomes
Leaf surface waxes
Thickness of cell well
Nutrient deficiency
NONGLANDULAR TRICHOMES Trichomes affect locomotion, attachment, shelter, feeding,
digestion and oviposition of insect and the effect depends on
density, length and shape of trichomes. Long hairs not only impede
movement, but also prevent the insect from reaching the leaf
surface to feed on.
Trichomes have basically three types of effects on insect behavior
over the leaf surface:
(1) simple impedance
(2) physical trapping by hooked hairs
(3) stickiness caused by exudates from the glandular
trichomes.
Smith et al (1975) showed that the rate of travel by the
first-instar larvae of the pink bollworm Pectinophora
gossypiella was more than six times faster on smooth
leaves the an on those with pubescence. Because of this
lack of movement, the larvae were deterred from the plant
substrate.
Hooked trichomes in French bean offer resistance, to
aphid, Aphis craccivora
Glandular trichomes are widely distributed in vascular plants that exude
gummy, sticky, or polymerizing chemical mixtures that severely impede the
insect's ability to move, feed, and/or survive.
A number of plants of the Solanum lycopersicon, Nicotiana and Medicago
spp, are particularly adept in producing sticky leaf exudates.
In certain wild potato species (Solanum polyadtnium,, S. berthaultii, and S.
tariyense), an exudate is discharged from the four-lobed head of the glandular
hairs when aphids Myzus persicac or Macrosiphum euphorbiae mechanically
rupture the cell wall (Gibson 1971)
Polyphenoloxidase and peroxidase activities are exhibited by the glandular
trichomes of S. berthaultii for oxidation of the phenolic compounds in
glandular exudates (Ryan et al 1982).
GLANDULAR TRICHOMES
LEAF SURFACE WAXES
Plant epicuticular waxes affect the feeding behavior of insects
particularly the settling of probing insects, acting as
phagostimulants or feeding deterrents. They also effect
colonisation and oviposition.
Ex: Wax bloom on leaves of crucifers deter feeding by
diamond back moth.
In onion glossy foliage provide more resistance to thrips.
THICKNESS OF CELL WELL
Cell walls thickening affect the feeding behavior of insects.
Examples:
Rice varieties containing thicker hypodermal layers offer
resistance to stem borer.
Stem density of pith and node tissues in wheat resists
damage by the wheat stem fly
Sorgham varieties resistant to shootfly due to the thickness
of the cell walls
NUTRIENT DEFICIENCY
The deficiency to the level of solids and nitrogenous
compounds in Canby an aphid resistant raspberry showed
delayed development, significantly reduced size, lower
fecundity, and extensive mortality in the aphids Amphorophora
agathonica (Hottes)
BIOCHEMICAL FACTORS
Several chemical constituents of plants that serve as
olfactory and gustatory stimuli, these may be
nutrients, sugars, amino acids, phospholipids, etc, or
non-nutritive constituents, i. e., glycosides, alkaloids,
terpenoids, etc. Such stimuli are specific and are
crucial in evoking the behavioral response of insects
(preference/antixenosis) to plants.
REPELLENTS
Plant defense compounds that prevent or reduce contact
between the insect and the substrate are known as
repellents.
Steam distillate of resistance rice varieties and nonhost
barnyard grass were found to repel Nilaparvata lugens.
The exudates from the glandular trichomes of Solanum
spp contain volatile substances Including
sesquiterpenes. These volatiles repel the aphid Myzus
persicae
ANTIBIOSIS
Adverse effect of the host plant on the biology (survival,
development and reproduction) of the insects and their
progeny due to the biochemical and biophysical factors
present in it.
Manifested by larval death, abnormal larval growth, etc.
Antibiosis may be due to
- Presence of toxic substances
- Absence of sufficient amount of essential nutrients
- Nutrient imbalance/improper utilization of nutrients
SYMPTOMS OF INSECTS AFFECTED BY ANTIBIOSIS INCLUDE
Death of young immatures
Reduced growth rate
Increased mortality in pupal stage
Small adults with reduced fecundity
Shortened adult life span
Morphological malformations
Restlessness and other abnormal behaviour
PRESENCE OF TOXINS:
Presence of toxic metabolites such as alkaloids and
glueosides play an important role in resistance to insects.
1. DIMBOA (Dihydroxy methyl benzoxazin)- Against European
corn borer, Ostrinia nubilalis
2. Gossypol (Polyphenol) -Helicoverpa armigera (American
bollworm)
3. Sinigrin - Aphids-Myzus persicae
4. Cucurbitacin -Cucurbit fruit flies
5. Salicylic acid -Rice stem borer
PRESENCE OF GROWTH INHIBITORS
Steriodal glycosides in potato and saponins in alfalfa
offer resistance to insects
Gossypol, the yellow polyphenolic pigment found in
the pigment glands of the genus Gossypium, is insect-
growth inhibitor that has resistant to the bollworm,
tobacco budworm, pink boll worm, and other tissue
borers.
NUTRITIONAL IMBALANCE
Reduction in the sugar content of the plant at the critical stages of
insect growth may adversely affect the insect.
Ex: larvae of the European, corn borer require glucose up to the
fourth instar and are capable of differentiating between varying
sugar concentrations to the, host plant tissues. Sugar deficiency
until this stage of larval development may cause antibiosis
Pea cultivars with low amino acids levels an increased sugar
content show resistance to pea aphid, Acyrthosiphon pisum
rice cultivars deficient in asparagines causes
reduced fecundity in brown plant hopper
STRUCTURAL FACTORS
Structural factors can serve as defense mechanisms for plants
when herbivores come in contact with them. The most
common contact factors that impart antibiosis resistance are
Plant-tissue toughness
Cell-wall composition
Proliferation of wounded tissues
PLANT-TISSUE TOUGHNESS
Toughness may reduce the suitability of leaves as a food source
for herbivores in several ways:
Indigestible polymers such as cellulose and lignin in secondary
tissues may reduce the rate of leaf consumption by herbivores.
Indigestible materials in tough leaves may be less suitable for
herbivore growth, development, and/or survival.
Nutrients such as proteins and carbohydrates may be less
available in tough leaves because of the hydrogen bonding
between these compounds.
Ex: Tough leaves of Salix babylonica and S. alba that can resist
tearing, erode the cutting surface of the incisors of the leaf beetle
Plagiodera versicolora
CELL-WALL COMPOSITION
The presence of neutral detergent fiber (NDF), lignin, and biogenic
silica in cell walls of plants can affect insect feeding at both
nutritional and physical level. Plants high cell wall structural
components are not desirable for herbivores (Scnber and Sansky
1981 ).
Elevated levels of indigestible fiber and silica may Increase the bulk
density of the diet to the extent that insect are
unable to ingest sufficient quantities of nutrients and water.
Ex: Silica in the rice leaves affect the feeding of stem
borer
PROLIFERATION OF WOUNDED TISSUES
Involve the proliferation of cells triggered by injury
or increased secretion 0f plant substances known to
cause the death of eggs or young larvae inside of
damaged plant
Ex: larvae of young pink bollworms were crushed or
downed by proliferating cells of the injured tissues
in certain corn line.
In mustard – necrotized zone around the base of
the egg of cabbage worm causing them desiccate.
TOLERANCE
Tolerance refers to the ability of the host plant to with
stand an insect population sufficient to damage severely
the susceptible plants.
Tolerance is a plant response to an insect pest. Whereas,
antibiosis and antixenosis resistance cause an insect
response when the insect attempts to use the resistant
plant for food, oviposition, or shelter.
This form of resistance include general vigour,
compensatory growth in individual plants and or the plant
population, wound healing, mechanical support in tissues
and organs and changes in photosynthate partitioning.
ADVANTAGES AND LIMITATIONS OF TOLERANCEAdvantages
Tolerant varieties have higher ETL
They prevent development of biotypes
They increase yield stability
Limitations
Insect populations are allowed to sustain epidemics in an
area, causing problems in other crops
It is more strongly affected by environmental extremes
than other forms of resistance
CONCLUSION The mechanism of resistance has three main
components that check the pest population from orientation, feeding and oviposition. These components are responsible for the development of resistance against various insect pest.
These resistance does not end with a generation of the insect pest, but lasts against successive generations.
These are eco-friendly and does not cause any pollution in component of the environment nor does it have any deleterious effect on man or wild life.