Plant Breeding for Pest Resistance

NCERT grounding

This subtopic is anchored in NCERT Class 12 Biology, Chapter 9 (Strategies for Enhancement in Food Production), section 9.2.3, titled Plant Breeding for Developing Resistance to Insect Pests. The textbook opens the section by naming insect and pest infestation as "another major cause for large scale destruction of crop plant and crop produce." It then states the central rule of the entire subtopic: insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics. Every cultivar example and every NEET question on this page traces back to that single classifying sentence.

"Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics. Hairy leaves in several plants are associated with resistance to insect pests, e.g., resistance to jassids in cotton and cereal leaf beetle in wheat."
— NCERT Class 12 Biology, §9.2.3

The chapter also gives a short table (Table 9.2) of released crop varieties bred for insect-pest resistance. That table is the source for the cultivar names this page treats in depth: Pusa Gaurav in Brassica, Pusa Sem 2 and Pusa Sem 3 in flat bean, and Pusa Sawani and Pusa A-4 in okra. Because this chapter has been rationalised out of the current NCERT, the old-NCERT supplement remains the authoritative syllabus source for NEET.

The three bases of insect resistance

Resistance of a host plant to insect pests is the plant's built-in capacity to escape, deter or survive insect attack. Unlike chemical pesticides, this resistance is heritable, costs the farmer nothing once the seed is sown, and does not break down with a single spray missed. NCERT classifies the underlying causes into exactly three groups, and a NEET candidate must be able to assign any given example to the correct group.

The first group, morphological, covers physical structures of the plant body: leaf hairs, stem solidity, leaf surface texture and the presence or absence of nectar. The second group, biochemical, covers the chemical composition of plant tissues: the levels of amino acids, nitrogen and sugars that determine whether the tissue is nourishing or hostile to a feeding larva. The third group, physiological, covers functional plant processes; NCERT names this category but does not elaborate it with an example, so candidates should remember the name itself.

The breeding programme itself does not change across these three bases. The breeder screens germplasm for a resistance source, crosses it into a high-yielding cultivar, and selects progeny that carry both the yield of the elite parent and the resistance trait. What changes is only the trait being tracked — whether the breeder is selecting for hairier leaves, solider stems or a particular tissue chemistry.

Morphological basis in detail

The morphological basis is the most heavily examined of the three because NCERT supplies four concrete structure–pest pairings. Each pairing must be memorised exactly: a wrong pest or a wrong crop is a wrong answer in a NEET match-the-column item.

Hairy leaves

Dense hairs (trichomes) on the leaf surface form a physical screen. Small sap-sucking and leaf-feeding insects cannot easily reach the epidermis to settle, feed or lay eggs, so they avoid hairy-leaved plants. NCERT gives two distinct pairings for hairy leaves: resistance to jassids in cotton, and resistance to the cereal leaf beetle in wheat. The same morphological feature therefore protects two different crops against two different insects, and NEET can ask either pairing.

Solid stems in wheat

The stem sawfly lays its eggs inside the hollow internodes of wheat, and its larva tunnels along the pith cavity. A solid stem — an internode filled with pith rather than hollow — leaves the larva no cavity to bore into. NCERT phrases this precisely: in wheat, "solid stems lead to non-preference by the stem sawfly." The word non-preference matters; the insect is not killed, it simply chooses not to lay eggs in such stems.

Smooth-leaved and nectarless cotton

Cotton bollworms are attracted to cotton plants partly by leaf surface and by extrafloral nectar. NCERT states that smooth-leaved and nectarless cotton varieties do not attract bollworms. Two structural features act together here: a smooth (rather than hairy or rough) leaf surface and the absence of nectaries. The absence of the reward and the cue reduces the bollworm's tendency to colonise the crop.

Biochemical and physiological basis

Where the morphological basis works by physical barriers, the biochemical basis works through tissue chemistry. An insect larva boring into a stem depends on that tissue for nutrition. If the chemistry of the tissue is wrong — too poor in the nutrients the larva needs, or carrying the wrong balance of compounds — the larva grows slowly or fails to establish.

NCERT gives one precise example. In maize, the combination of high aspartic acid, low nitrogen and low sugar content leads to resistance to maize stem borers. All three chemical conditions must be recalled together: high aspartic acid, low nitrogen, low sugar. Nitrogen and sugar are the nutrients the borer larva relies on, so lowering them starves the pest; the raised aspartic acid is the associated marker NCERT lists alongside.

The physiological basis is the third category named in §9.2.3. NCERT lists it in the classifying sentence but does not develop it with a crop example, unlike the morphological and biochemical categories. For NEET purposes the safe approach is to know that there are three bases — morphological, biochemical and physiological — and that physiological is the one without a textbook-supplied illustration. A question that asks "which is NOT a basis of insect resistance" is testing exactly this list of three.

Released insect-resistant cultivars

NCERT Table 9.2 lists three crops with released insect-resistant varieties. These cultivar names are high-frequency NEET material because they pair a named variety with a named pest in a way that suits match-the-column questions. Each variety carries the prefix "Pusa," reflecting its development at the Indian Agricultural Research Institute, New Delhi.

Brassica — Pusa Gaurav

Pusa Gaurav is a variety of Brassica (rapeseed mustard) bred for resistance to aphids. Aphids are sap-sucking insects, and a resistant mustard variety reduces the colony build-up that otherwise drains the crop. Pusa Gaurav is the single entry NEET candidates link to "aphids" in the insect-pest table, distinct from the disease-resistance variety Pusa Swarnim of the same crop.

Flat bean — Pusa Sem 2 and Pusa Sem 3

Flat bean, also called sem, has two released varieties — Pusa Sem 2 and Pusa Sem 3 — bred for resistance to a cluster of three pests: jassids, aphids and fruit borer. This is the broadest pest list in the table; a single flat-bean variety is resistant to three named insects at once, so a question can pair Pusa Sem with any of the three.

Okra (bhindi) — Pusa Sawani and Pusa A-4

Okra, the bhindi of Indian kitchens, has two released varieties — Pusa Sawani and Pusa A-4 — bred for resistance to shoot and fruit borer. The shoot and fruit borer is the principal insect pest of okra, attacking both the growing shoot and the developing fruit, which is why both organs are named in the resistance.

How breeders develop these varieties

NCERT is explicit that the method of breeding for insect-pest resistance is not special: it "involves the same steps as those for any other agronomic trait such as yield or quality." The breeder is simply tracking a resistance trait through the standard plant-breeding workflow rather than tracking yield. The sources of the resistance genes are also stated: cultivated varieties, germplasm collections of the crop, or wild relatives.

Because the workflow is shared, a NEET question on the method of insect-resistance breeding is effectively a question on general plant-breeding steps. What is unique to this subtopic is the trait being selected and the morphological or biochemical character that signals it. Knowing that hairy leaves, solid stems, smooth nectarless surfaces and a particular maize tissue chemistry are the resistance markers is the part that cannot be answered from the general breeding chapter.

Worked examples

Common confusion & NEET traps

The mistakes NEET candidates make on this subtopic are almost all errors of pairing — assigning the right trait to the wrong pest, or confusing an insect-resistance variety with a disease-resistance variety of the same crop. The traps below isolate the recurring confusions.