🐞 Host Plant Resistance

Host plant resistance is a core IPM strategy that uses heritable plant traits to reduce pest injury while preserving ecological balance and reducing insecticide dependence. This lesson covers the types, mechanisms, compatibility, and practical crop examples of host plant resistance.

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). “Those heritable characteristics possessed by the plant which influence the ultimate degree of damage done by the insect” (Maxwell, F.G., 1972).

Types of Resistance

Ecological Resistance or Pseudo resistance

Apparent resistance resulting from transitory characters in potentially susceptible host plants due to environmental conditions. Pseudoresistance may be classified into 3 categories a . Host evasion Host may pass through the most susceptible stage quickly or at a time when insects are less or evade injury by early maturing. This pertains to the whole population of host plant. b. Induced Resistance Increase in resistance temporarily as a result of some changed conditions of plants or environment such as change in the amount of water or nutrient status of soil c. Escape Absence of infestation or injury to host plant due to transitory process like incomplete infestation. This pertains to few individuals of host.

Genetic Resistance

A. 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 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. The cumulative effect of minor genes is called adult resistance or mature resistance or field resistance. Also called horizontal resistance B. Based on biotype reaction

• Vertical resistance: Effective against specific biotypes (specific resistance)

• Horizontal resistance: Effective against all the known biotypes

(Non specific resistance)

C. Based on population/Line concept

• Pureline resistance: Exhibited by liens which are phenotypically and genetically

similar

• Multiline resistance: Exhibited by lines which are phenotypically similar but

genotypically dissimilar

D. 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.

E. Based on evolutionary concept

• Sympatric resistance: Acquired by coevolution of plant and insect (gene for gene)

Governed by major genes

• Allopatric resistance: Not by co-evolution of plant and insect.

Governed by many genes

Mechanisms of Resistance

The three important mechanisms of resistance are

• Antixenosis (Non preference)

• Antibiosis

• Tolerance

Antixenosis: Host plant characters responsible for non-preference of the insects for

shelter, oviposition, feeding, etc. It denotes presence of morphological or chemcial factor which alter insect behaviour resulting in poor establishment of the insect. e.g. Trichomes in cotton - resistant to whitefly Wax bloom on carucifer leaves - deter feeding by DBM Plant shape and colour also play a role in non preference Open panicle of sorghum - Supports less Helicoverpa

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

Chemical factors in Antibiosis - Examples

Chemicals present in plants Imparts resistance against

1. DIMBOA (Dihydroxy methyl Against European corn borer, Ostrinia nubilalis

benzoxazin)

2. Gossypol (Polyphenol) Helicoverpa armigera (American bollworm)
3. Sinigrin Aphids , Myzus persicae
4. Cucurbitacin Cucurbit fruit flies
5. Salicylic acid Rice stem borer

Physical factors in antibiosis Thick cuticle, glandular hairs, silica deposits, tight leaf sheath, etc.

c. Tolerance Ability to grow and yield despite pest attack. It is generally attributable to plant vigour, regrowth of damaged tissue, to produce additional branches, compensation by growth of neighbouring plants.

Use of tolerance in IPM

• Tolerant varieties have high ETL - require less insecticide

• Apply less selection pressure on pests. Biotype development is less

HPR in IPM

• HPR is a very important component of IPM

• Selection and growing of a resistant variety minimise cost on all other pest management activities

Compatibility of HPR in IPM

a. Compatability 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 is sufficient to control insects on resistant variety b. Compatibility with biological control

• Resistant varieties reduce pest numbers - thus shifting pest: Predatory (or parasitoid) ratio favourable for biological control. e.g. Predatory activity of mirid bug Cyrtorhinus lividipennis on BPH was more on a resistant rice variety IR 36 than susceptible variety IR 8

• Insects feeding on resistant varieties are more susceptible to virus disease (NPV) c. Compatibility with cultural method

• Cultural practices can help in better utilization of resistant varieties. e.g. Use of short duration, pest resistant plants effective against cotton boll weevil in USA.

Examples of resistant varieties in major crops

Resistant varieties TKN 6, Paiyur 1 CO 42, IR 36, IR 64

Rice

Sugarcane

Cotton

Pest Yellow stem borer Brown planthopper (BPH)

Top shoot borer CO 745, CO 6515 American bollworm Abhadita

Spotted bollworm Deltapine Stem weevil MCU 3, Supriya

Green leaf hopper (GLH) IR 50, Ptb 2, CO 46 Early shoot borer (ESB) CO 312, CO 421, CO 661,

Internode borer CO 975, CO 7304

Top shoot borer American bollworm

Spotted bollworm Deltapine Stem weevil MCU 3, Supriya

Leaf hopper MCU 5, K 7, K 8 Sorghum Earhead bug K tall Jasmine Eriophyid mite Pari Mullai

Earhead bug Eriophyid mite

K tall Pari Mullai

Advantages of HPR as a component in IPM

Specificity: Specific to the target pest. Natural enemies unaffected Cumulative effect: Lasts for many successive generations Eco-friendly: No pollution. No effect on man 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 Compatability: HPR can be combined with all other components of IPM Decreased pesticide application: Resistant varieties requires less frequent and low

doses of insecticides Persistence: Some varieties have durable resistance for long periods Unique situations: HPR effective where other control measures are less effective

e.g. a. When timing of application is critical

b. Crop of low economic value c. Pest is continuously present and is a single limiting factor

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

lastmod: 2026-05-24T00:00:00+05:30

Summary Cheat Sheet

• Host plant resistance protects crops through heritable traits that reduce pest damage without relying only on insecticides.

• Major resistance mechanisms are antixenosis, antibiosis, and tolerance.

• Resistance may be pseudoresistance or genetic resistance, and may involve single genes or multiple genes.

• Review core concepts, definitions, and field-level application points from this lesson.

• Prioritize economic threshold-based decisions and integrated management logic where relevant.