Merits and Demerits of Resistance Breeding
Merits:
There are several merits and demerits of breeding for insect and disease resistance. Some merits and demerits of resistance breeding are given below:
1. Resistant varieties play an important role in controlling the losses caused by diseases and insects in crop plants. About 14% annual losses of potential crop yield are caused by insect pests and about 20-30 % losses are caused by various diseases. These losses can be minimized through the use of resistant varieties.
2. Resistant varieties lead to reduction in the cost of production resulting in increasing the cost benefit ratio. Use of resistant varieties leads to reduction in the use of pesticides which in turn results in reduction of environmental pollution and health hazards caused by the use of pesticides. Moreover, genetic resistance protects natural enemies of insect pest which are killed through the use of insecticides.
3. Resistant varieties are non toxic to man, farm animals and wild life. In other words , resistant varieties do not contain pesticide residues which are toxic to man, farm animals and wildlife.
4. Genetic resistance is the only solution of some diseases such as wilts, rusts, smuts, nematodes and bacterial blights.
Demerits:
1. It is a long term process which takes 10-15 years to develop agronomically acceptable variety even when the source of resistance are readily available.
2. In some cases, breeding for resistance to one pest leads to the susceptibility to another pest. This is because the host plant feature associated with resistance to one insect is associated with susceptibility to another insect. For example, hairiness ,in cotton is associated with Jassid resistance but confers susceptibility to whitefly and bollworms.
3. In many cases, genes for disease and insect resistance are available only in the related wild species. Interspecific gene transfer poses many problems. Moreover, resistant genes are associated with some undesirable characters. It takes a long time to discard undesirable genes in a breeding programmes.
4. Breeding for disease and insect resistance is an expensive method which requires adequate financing for a long period being a long term process. Often lack of funds leads to the interruption of such valuable programmes.
5. In some cases, the resistant variety has lower yield and poor quality. For example ‘Rescue’ a stem sawfly resistant variety of wheat, developed in USA has lower yield and poor gain quality than sawfly susceptible varieties in the absence of sawfly incidence. In such situation a crop rotation of resistant and high yielding susceptible variety is adopted. A two years Rescue- three years high yielding susceptible variety rotation will keep the sawfly to an acceptable level and help in realization of good wheat yield.