Host Plant Resistance

1. LECTURE 1 TITLE: Host Plant Resistance – Types and Mechanisms of Resistance and its Applications Dr. W. BABY RANI Professor

Agricultural Entomology
Tamil Nadu Agricultural University
State: Tamil Nadu
India
Former Student- Plant Protection Faculty, Ukraine Agricultural Academy, Kyiv 1984 -1989.
Former Dean of Sethu Bhaskara Agricultural College and Research Foundation, TNAU.
Former Professor and Head of Coastal Saline Research Institute, TNAU, Ramnad.
Former Professor and Head, Plant Protection, AEC&RI, TNAU, Tiruchirappalli.

2. Mechanisms of Host Plant Resistance- and Its Applications

TITLE
Host Plant Resistance – Types and Mechanisms
of Resistance and its Applications
LECTURE 1
Mechanisms of Host Plant Resistance- and Its
Applications
Mechanisms of Host Plant Resistance Types of Resistance
Applications
Advantages
Disadvantages

3.

Host Plant Resistance (HPR)
Definition
• Those characters that enable a plant to avoid, tolerate
or recover from attacks of insects under conditions
that would cause greater injury to other plants of the
same species” (Painter, R.H., 1951)

4.

Types of Resistance
• Ecological Resistance or Pseudo resistance
– Apparent resistance resulting from transitory characters in
potentially susceptible host plants due to environmental
conditions
• Genetic Resistance
– Heritable change in plants based on number of genes, reaction
to biotypes, and population

5.

Ecological/Pseudo resistance -classified into 3 categories
• Host evasion
– Host may pass through most susceptible stage quickly or at
a time when insects are less or
– Evade injury by early maturing
• Induced Resistance
– Increase in resistance temporarily as a result of some
changed conditions of plants or environment such as
change in amount of water or nutrient status of soil
• Escape
– Absence of infestation or injury to host plant due to
transitory process like incomplete infestation

6.

Genetic Resistance
Based on number of genes
• Monogenic resistance
– Controlled by single gene
– Easy to incorporate into plants by breeding
– Easy to break also
• Oligogenic resistance
– Controlled by two or few genes
• Polygenic resistance
– Controlled by many genes
• Major gene resistance
– Controlled by one or few major genes (vertical resistance)
• Minor gene resistance
– Controlled by many minor genes
– Cumulative effect of minor genes -called adult resistance or
mature resistance or field resistance
– Also called horizontal resistance

7.

Genetic Resistance
Based on biological races / biotypes reaction
• Non-interbreeding sympatric populations (having overlapping
ranges) differ in biology but not, or scarcely, in morphology;
• Supposedly prevented from interbreeding by preference for
different food plants or other hosts

8.

Genetic Resistance
Based on biological races / biotypes reaction
• Vertical resistance
– Controlled by single dominant gene
– Effective against specific biotypes (specific resistance)
– Easy to incorporate into genetic make-up of commercially acceptable
crop plant varieties
– Effective to one or very few pests
• Horizontal resistance
– Polygenic
– Effective against all the known biotypes (Non specific resistance)
– Improvement in crops with horizontal resistance-a building process
based on stepwise accumulation of genes with favourable additive
effects
– Relative or quantitative
– Has advantage of stability-not under pressure of attack by different
strains of pest species in different localities and over time
– Effective against larger number of pests
– Durable resistance
– Resistance for longer period of time

9. Biotype

• A genetically distinct strain / subgroup of a species distinguished
by some behavioural / physiological difference but
indistinguishable morphologically
• Applied to strains of insect species which can overcome resistant
plants
• Biotype problem - commonly observed in aphids which are
among the fastest breeding pests
• Biotypes -a particular problem for host plants that show vertical
resistance to pests
• Monogenic vertical resistance - highly likely to drive the
development of new biotyes, most notably where the primary
resistance mechanism is antibiosis
• Insect biotypes -developed mostly among hemipterous pests
• Brown plant hopper (BPH) and grape phylloxera
• In general problems with biotype development -relatively rare.

10.

Genetic Resistance
Based on population/Line concept
• Pure line resistance
– Exhibited by lines which are phenotypically and genetically
similar
• Multiline resistance
– Exhibited by lines which are phenotypically similar but
genotypically dissimilar
Miscellaneous categories
• Cross resistance
– Variety with resistance incorporated against a primary pest,
confers resistance to another insect
• Multiple resistance
– Resistance incorporated in a variety against different
environmental stresses like insects, diseases, nematodes,
heat, drought, cold, etc.

11. Mechanisms of Resistance

Three important mechanisms of resistance:
• Antixenosis (Non preference)
• Antibiosis
• Tolerance

12.

Antixenosis (plant morphological characters)
• Host plant characters responsible for non-preference of insects for
shelter, oviposition, feeding
• Denotes presence of morphological or chemical factor which alter
insect behaviour resulting in poor establishment of the insect
• Trichomes in cotton - resistant to whitefly
• Wax bloom on crucifer leaves - deter feeding by Diamond Back
Moth(DBM)
• Plant shape and colour -play a role in non preference
• Open panicle of sorghum - Supports less preference by Helicoverpa

13.

Antibiosis
• Adverse effect of host plant on biology (survival, development and
reproduction) of insects and their progeny due to biochemical and
biophysical factors present in plants
• Manifested by larval death, abnormal larval growth, etc.
• Antibiosis-due to presence of toxic substances, absence of sufficient
amount of essential nutrients, and nutrient imbalance/improper
utilization of nutrients
• Chemical factors in Antibiosis or chemicals present in plants that
imparts resistance against insects pests are:
– DIMBOA (Dihydroxy methyl benzoxazin) -against European corn
borer, Ostrinia nubilalis
– Gossypol (Polyphenol) –cotton -Helicoverpa armigera
– Sinigrin - Aphids, Myzus persicae
– Cucurbitacin – Cucurbit fruit flies
– Salicylic acid - Rice stem borer
• Physical factors in antibiosis
– Thick cuticle, glandular hairs, silica deposits, tight leaf sheath, etc.

14.

Tolerance
• Ability to grow and yield despite pest attack
• Generally attributable to plant vigour, re-growth of damaged
tissue, to produce additional branches, compensation by
growth of neighboring plant
Use of tolerance in IPM
• Tolerant varieties have high ETL - require less insecticide
• Apply less selection pressure on pests
• Biotype development - less

15.

Applications
HPR in IPM
• Selection and growing of a resistant variety minimizes cost on
all other pest management activities
Compatibility of HPR in IPM
• Compatibility with chemical control
– HPR enhances efficacy of insecticides
– Higher mortality of leaf hoppers and plant hoppers in
resistant variety compared to susceptible variety
– Lower concentration of insecticide-sufficient to control
insects on resistant variety

16.

HPR in IPM (Contd.)
• Selection and growing of a resistant/tolerant variety minimises
cost on all other pest management activities
• Compatibility with biological control
– Resistant/tolerant varieties reduce pest numbers
– Shifting pest: Predatory (or parasitoid) ratio favourable for
biological control
– e.g. Predatory activity of mirid bug Cyrtorhinus lividipennis
on Rice BPH - more on a resistant rice variety IR 36 than sus.
variety IR 8
– Insects feeding on resistant varieties-more susceptible to
virus disease (NPV)
– Note: BPH –Brown plant hopper
– IR - International Rice
– NPV- Nuclear Polyhedra virus – Entomopathogenic virus

17.

HPR in IPM (Contd.)
• Selection and growing of a resistant variety minimises cost on all
other pest management activities
• Compatibility with cultural method
– Cultural practices help in better utilization of resistant
varieties
– e.g. Use of short duration, pest resistant crop plants effective
against cotton boll weevil in USA

18.

Examples of resistant/ Tolerant varieties in major crops
• Rice
– Yellow stem borer (YSB)- TKM 6, IR 20, Paiyur 1, Ptb 36
– Leaf folder – TKM 6
– Brown planthopper (BPH) - CO 42, ADT 36, PY3, IR 36, IR 64
– Green leaf hopper (GLH) - IR 50, Ptb 2, CO 46
– Gall midge (GM)– MDU 3
• Sugarcane
– Early shoot borer (ESB) - CO 312, CO 421, CO 661, CO 917
and CO 853
– Internode borer - CO 975, CO 7304, and COJ 46
– Top shoot borer - CO 745, CO 6515 and C0 419, and
– tolerant varieties CO 859, CO 1158 and CO 7224

19.

Examples of resistant varieties in major crops
(Contd.)
• Cotton
– American bollworm- Mahalakhshmi, LH 900, Krishna, Vijay,
Sujatha, Sujay, LHA5, UK 48, Hopi, Deltapine, Abhadita,
Transgenic Boll gourd
– Spotted bollworm – Deltapine
– Stem weevil - MCU 3, Supriya
– Leaf hopper - MCU 5, K 7, K 8, Anjali, Chairy
– Whitefly - Kanchana
• Sorghum
– Earhead bug - K tall
– Shoot fly- C01 and CSH 15 R
• Jasmine
– Eriophyid mite - Pari Mullai

20.

Advantages of HPR as a component in IPM
Specificity: Specific to target pest. Natural enemies unaffected
Cumulative effect: Lasts for many successive generations
Eco-friendly: No pollution. No effect on humanbeings and animals
Easily adoptable: High yielding insect resistant variety easily accepted
and adopted by farmers. Less cost
Effectiveness: Res. variety increases efficacy of insecticides and
natural enemies
Combined with all other components of IPM
Requires less frequent and low doses of insecticides
Some varieties have durable resistance for long periods
HPR effective where other control measures- less effective
– When timing of application critical
– Crop of low economic value
– Pest continuously present and a single limiting factor

21.

22.

Disadvantages of HPR
• Time consuming
– Requires from 3-10 years by traditional breeding
programmes to develop a res. variety
• Biotype development
– A biotype is a new population capable of damaging and
surviving on plants previously resistant to other
population of same species
• Genetic limiation
– Absence of resistance genes among available
germination