1. Welcome
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2. Morphological and
biochemical characters of
plants providing resistance
against insect pests
Advisor-
Dr. V K Rana
Submitted by-
Harmanjot Singh
M.Sc. Agri (Entomology)- Sem III
NH-2019-08-M
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3. INTRODUCTION
• Host plant resistance involves conventional approaches and
phenomenon of inter-relationship between host plants and affected
by environmental factors.
• It is the relative amount of heritable qualities that influence the
ultimate degree of damage done by the insects (Painter, 1951).
• Plant resistance is defined as the heritable characters possessed by
the plant which influences the ultimate degree of damage done by
the insects (Maxwell, 1972).
• Resistance to insects is the inheritable property that enables a plant
to inhibit the growth of insects population (Kogan, 1982). 3

4. ADVANTAGES
1) Resistance variety is a good IPM tool and
ecologically safer.
2) Specificity– Host specific. E.g. Hessian fly resistant
variety “Underhill”
3) Resistance is persistent until it is broken by some
factors.
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5. 4) Easy to adopt
5) Compatible with other methods
 Resistance variety
 Early/late sowing
 Irrigation/trace condition
 Application of insecticides
7) Keep pest population at low level
 Morphological characters
 Chemical composition
 Remained population more vulnerable with chemical/natural
enemy.
8) Number of insecticides applications reduced.
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6. MECHANISM OF RESISTANCE
• R.H. Painter classified mechanism of resistance into 3
main categories –
1) Antixenosis (Non preference)
2) Antibiosis
3) Tolerance
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7. ANTIXENOSIS
It refers to plant characteristics that lead insects away from
a particular host. It is also known as non preference.
Types of Non-preference:
a) Morphological non-preference
b) Allelochemic non-preference
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8. ANTIBIOSIS
It refers to the adverse effect of the host plant on the
biology of the insects and their progeny infesting it
due to the bio-chemical and bio-physical factors
present in it.
Symptoms of insects affected by antibiosis include:
• Death of young immatures
• Reduced growth rate
• Small adults with reduced fecundity
• Shortened adult life span
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9. These symptoms may appear due to
various physiological processes such as:
• Presence of toxic metabolites.
Eg: Corn is resistant to corn borer due to the presence of 2,4-
dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA).
• Absence/insufficiency of essential nutrients.
Eg: Rice cultivars deficient in asparagines causes reduced fecundity
in brown plant hopper.
• Presence of antibodies.
Eg: Cotton varieties rich in gossypol offer resistance to bollworms.9

10. TOLERANCE
• It 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.
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11. ADAPTATIONS IN PLANTS
FOR RESISTANCE
I. MORPHOLOGICAL BASES (ANTIXENOSIS)
II. BIOCHEMICAL TRAITS (ANTIBIOSIS)
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12. (I) MORPHOGICAL TRAITS
The morphological characteristics of a plant which
confer resistance to insect pests are-
i. Trichomes on plant surface
ii. Surface waxes
iii. Hardness of plant tissues
iv. Thickening of cell walls and cutical
v. Colour
vi. Shape and size
vii. Pubescence
viii. Frego bract
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13. 1. TRICHOMES
• The epidermis of the plants bears hair like outgrowth
called trichomes or hairs.
• Found on leaves, shoots and roots of plants.
• Trichomes occur in several forms, shape and sizes.
• Trichomes affect locomotion, attachment, shelter,
feeding, digestion and oviposition of insects.
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14. PICTURE OF
TRICHOMES
E.g.: Hooked trichomes in French bean offer resistance to
aphids, Aphis craccivora
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15. TYPES OF TRICHOMES
1.1 Glandular trichomes
1.2 Non glandular trichomes
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16. 1.1 GLANDULAR TRICHOMES
• Glandular trichomes are secrete chemicals which are
toxic to insects. These are generally found in
dicotyledonous.
• Trichomes exudates from the leaves of Nicotiana and
Petunia spp. are highly toxic to the tobacco hornworm.
• It exudates contain large variety of non volatiles such as
alkaloids and phenolics and volatiles such as terpene oils
and other essential oils, which act as insect repellents in
plants. 16

17. GLANDULAR TRICHOMES (TOMATO LEAVES)
Eg: Adults of Whitefly, Bemisia tabaci were found trapped
by the glandular hairs on tomato leaves (Kisha, 1984) 17

18. 1.2 NON GLANDULAR TRICHOMES
• The non glandular trichomes are known to affect
locomotion, attachment, shelters, feeding and survival
of insects.
• Long hairs not only impede movement, but also prevent
the insect from reaching the leaf surface to feed on.
• Trichomes basically have three types of effects on insect
behaviour over the leaf surface:
1. Simple impedance
2. Physical trapping by hooked hairs
3. Stickiness caused by exudates from glandular
trichomes.
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19. Non-Glandular Trichromes (Okra)
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20. 2. SURFACE WAXES
• Waxes are esters formed by a linkage of a long chain
fatty acids and an aliphatic alcohol.
• Surface waxes over the epicuticle protect the plant
surface against insect feeding and diseases.
• Epicuticle waxes affect the feeding behaviour of
insects, particularly the settling of probing insects,
acting as phagostimulants or feeding deterrents.
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21. EXAMPLES
• Wax surface on leaves of crucifers deter feeding by
diamond back moth.
• In onion glossy foliage provide more resistance to
thrips.
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22. 3. COLOUR
• The colour and shape of plants affect host selection
behaviour of phytophagous insects and have been
associated with some resistance.
For example-
a. Yellow colour is preferred by aphids.
b. Green and blue colour is preferred by cabbage butterfly.
c. Dark green colour preferred by rice leaf folder.
• Harris and Miller (1983) reported that onion fly, preferred
to lay eggs around yellow onion stems.
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23. Dark green colour preferred by
rice leaf folder 23

24. 4. THICKENING OF CELL WALLS AND
CUTICAL
• Toughness and thickness of various plant parts adversely
affect the penetration and feeding of insects.
Example:
In sugarcane, varieties with very strong hard mid ribs in
their leaves were found resistant to sugarcane top borer,
as compare to those with weak mid ribs (Isaac, 1939 and
Adlakha,1964).
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25. • Rice varieties containing
thicker hypodermal layer
offer resistance to stem
borer.
• Sorghum varieties resistant
to shoot fly due to thickness
of cell walls.
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26. 5. PLANT PUBESCENCE
• Insects 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
constitutes the foremost host plant resistance.
• Pargell et al. (1949) demonstrated that greater hairiness to both
upland cotton and Egyptian cotton related to jassid resistance.
• Soyabean varieties with a dense hairiness of foliage can manifest
both antixenosis to oviposition and feeding deterrence against
leafhopper.
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27. Soyabean varieties with dense
hairiness
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28. 6. 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 (Jenkins and Parrot
1971).
• In field experiments, frego bract cotton showed 50% less
damage from oviposition than normal cottons. The role of
the frego bract in reducing damage by the boll weevil
appears to be due to some adverse effect on insect
behaviour.
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29. FREGO BRACT IN COTTON
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30. (II) BIOCHEMICAL BASES
• The biochemical bases of resistance can be divided into
two broad categories;
Behavioural responses
Physiological responses of insects.
• Insect behaviour modifying chemicals are further divided
into attractants, arrestants, repellents and deterrents.
• While plant chemicals affecting the physiological
processes of insects may be classified as nutrients,
physiological inhibitors and toxicants (Hsiao, 1969).
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31. Behaviour modifying chemicals
S.No Allelochemicals Effect on behaviour
I ALLOMONES Adaptive advantages
1 Repellents Orient insect away from
host plant
2 Locomotor excitants They speed up
3 Supressants Inhibit biting and piercing
4 Deterrents Prevent feeding and
oviposition
5 Antibiotics Disrupt normal growth
6 Antixenotics Disrupt host selection
behaviour
II KAIROMONES Adoptive advantages
1 Attractants Orient insect toward the
host
2 Arrestants Slow down and stop
movements
3 Oviposition excitants Effect oviposition 31

32. Insect behaviour modifying chemicals
• These are all secondary metabolites, i.e., chemicals that are
not required for the general growth and maintenance of the
plant but which serve as plant defence products.
• The types of chemicals responsible for insect resistance are
numerous but the major classes include the terpenoids,
flavonoids, quinones, alkaloids and glucosinolates.
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33. 33
Classification of secondary plant metabolites

34. • The organic isothiocyanates (mustard oils) are the main
biologically active catabolites from the glucosinolate
components of crucifers, which like other glucosinolates
defend plants against generalized insects including aphids
and grasshoppers (Panda and khush, 1995) but can also act
as phagostimulants and as kairomones, crucifers specific
hosts (Dawson et al., 1993).
• Some primary and intermediate metabolites such as citric
acid and cysteine can act in plant defence chemistry.
(Jager et al., 1996).
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35. Plant chemicals affecting the
physiological processes
There are a number of examples of plant chemicals that
have been used in promoting resistance to insects.
• Gossypol is a polyphenolic yellow pigment of cotton plants
that shown to confer antibiotics resistance to Helicoverpa zea
and H. virescens (Kumar, 1984)
• Experiment has been shown that the gossypol content of
cotton buds increased genetically from a normal 0.5% to
1.5% and a larval mortality of 50% is expected when cotton
square gossypol content is increased above 1.2% (Schuster,
1980)
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36. 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 pests.
• 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 components of the environment nor does
it have any deleterious effect on man or wild life. 36

37. THANKS
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