Authors: *Kana Ram Kumawat, Ravi Kumawat and Madhu Choudhary
Department of Plant Breeding and Genetics, S.K.N. Agriculture University
Jobner-303329, Jaipur, Rajasthan, India
*Email: kanaramkumawat8@gmail.com
The breeding for insect resistance is most important because many crops in India and other countries are affected by various kinds of insect families. For example the cotton crop is attacked by more than 160 species of insects of these a dozen are major pests.
Objectives / necessities for insect resistance breeding:
The necessities/objectives for insect resistance breeding are following:
- It indirectly prevent from environmental pollution
- It prevents from the death of beneficial predators and parasites due to chemicals harmful to them.
- It prevents from the higher costs involved in spraying of various chemicals
- For building up of resistance- e.g. Pyrethroid
Mechanism of insect resistance:
According to Painter (1951) the mechanism of insect resistance may be of four types viz., Non preference, Anti biosis, Tolerance and Avoidance
1. Non preference: This mechanism is unsuitable or unattractive for colonization, oviposition or both by an insect pest. This is also known as non-acceptance or antixenosis. Aphid resistance in raspberry is a good example of this mechanism. It involves various morphological and biochemical features of host plants.
2. Antibiosis: This is the adverse effects caused by the host plant to an insect feeding on it. It may hinder the development, reproduction or in some cases death also. The antibiosis may be either a) Morphological b) Physiological or c) Biochemical features of the host plant. Gossypol content in cotton is the good example of this mechanism.
3. Tolerance: In this mechanism the host plant is able to tolerate the attack, withstand and give normal yield.
4. Avoidance: In this mechanism the insects avoid certain plants. For example early maturing cotton varieties escape pink bollworm and Sorghum early lines escape shoot fly attack.
Nature of insect resistance:
Plants have some features for insect resistance like-
1. Hairiness: The hairiness of leaves is associated with insect resistance. E.g. Jassid resistance in cotton is good example.
2. Colour of plant: Colour induces non-preference for oviposition. E.g. Red cabbage is for lepidopteran insects and red colour cotton for boll worms.
3. Thickness of plant tissue: Thickness of plant tissue is also associated with insect resistance. Jassid resistance in case of cotton is good example of this feature. Dense thick leaves are more of mechanical obstruction.
4. Presence of silica in plant: Shoot fly resistance in sorghum is due to presence of silica which causes damage to mandibles of insect.
5. Biochemical factors: Some biochemical attributes are associated with insect resistance like Gossypol content in cotton and DIMBOA content in leaves of maize which disfavour stem borer.
6. Physiological factors: Osmotic concentration of cell sap, cell exudaters etc are associated with resistance to insect pests. For example aphids are trapped in gum exudates of Solanum species.
Genetics of Insect resistance:
The insect resistance may be of three types viz., (a) Oligogenic or Monogenic e.g. Jassid resistance in cotton and wheat rust resistance (b) Polygenic which is more durable e.g. wheat cereal leaf beetle resistance and (c) Cytoplasmic which is associated with plasmagenes e.g. European corn borer in maize.
Sources of resistance:
Cultivated varieties (like TKM-6 for rice stem borer resistance), germplasm collection and related wild species (like Sorghum nitidum for shoot fly resistance in sorghum and Gossypium anamalum for jassid resistance in cotton are some important sources to develop resistance.
Screening techniques: These may be some important techniques for resistance.
1. Field condition:
- Infector rows are planted at regular intervals
- Testing in areas wherever the pest is recorded as endemic area
- Seasonal testing when insect population is most.
- Rearing the insect in laboratory and releasing them in fields or by transferring equal number of eggs of larvae to each plant.
2. Glass house screening: Raised in cages and definite numbers of larvae are released in the cage.
Conclusions:
The breeding for insect resistance is most important because many crops in India are affected by various insects. The farmers have to use resistant varieties for growing the crops and plant breeders need to develop resistant genotypes using various sources as described earlier.
References:
1. Singh, B.D. (2015) Plant Breeding Principles and Methods. 10th Revised Edition, Kalyani publishers, New Delhi.
2. Internet (IASRI)
About Author / Additional Info:
Post-Graduated in subject of Plant Breeding and Genetics from SKNAU, Jobner