Plant Breeding- an introduction

Introduction in plant breeding  

All the major crops worldwide are the result of repetitive process of plant breeding. In plant breeding introduction refers to transposition of crop plants from the place of their cultivation to such areas where they were never grown earlier. Plant introduction consists of taking a genotype or a group of genotypes of plant into a new area or region where they were not being grown before.

Introduction is of two types, primary and secondary. When introduced variety is well adapted to the new environment, it is release for commercial cultivation without any alternation in the original genotypes, is referred to as primary introduction. For example semi-dwarf Triticum aestivum varieties Sonora 64. When the introduced variety may be subjected to selection to isolate a superior variety to get a superior variety, then it is called a secondary introduction. For example, in Triticum aestivum, varieties Kalyan Sona and Sonalika were released after selection from the material received from Mexico. Secondary introduction is more common than primary introduction.

Purpose of plant introduction :

 Plant introduction is the oldest and very effective breeding method to create gene variety. The main purpose of plant introduction is to improve the plant wealth of country. It makes a available to the breeders the germplasms required by them for their breeding programmes. The chief objectives of plant introduction are briefly described below.

(i) Entirely new crops :

Plant introduction may provide an entirely new crop species. many of our important crops, e.g. Zea mays, Lycopersicon esculentum etc are introductions. Some recently introduced crops are Glycine max, gobhi sarson (Brassica napus), Karan sarson (Brassiuca carinata) Ithiopion mustard etc.

(ii) New varieties:

Sometimes introductions are directly released as superior commercial varieties. The Mexican semidwarf wheat varieties Sonora 64 and Lerma Rojo, semidwarf rice varieties TN 1 and IR 8 etc are more recent example of this type.

(iii) utilization in crop improvement programmes :

It is often utilized in crop improvement programme. The introduced material are hybridised with local varieties to develop improved varieties. For example pusa ruby tomato was derived from a cross between meeruty and Sioux, an introduction from U.S.A.

(iv) Saving a crop from a disease or pest :

Sometimes a crop is introduced into a new area to protect it from a disease or pest. For example coffee was introduced in south America from Africa to prevent losses from leaf rust. Hevea rubber, on the other hand was brought to Malaya from South America to protect it from a leaf disease.

(v) Utilization in scientific study :

Collections of plants have been used for study of buiosystematics, evolution and origin of plant species.

(vi) Conservation of diversity :

The genetic diversity of crop plants is gradually being eroded due to evolution, deforesting, development of township and various others factor. Introduction of crop plant is useful in conservation of crop genetic diversity and saving certain species from extinction.

(vii) Used for aesthetic value :

Ornamentals, shrubs and lawn grass are introduced to satisfy the finer sensibilities of man. These plants are used for decoration and are great value in social life eg. Polyalthea.

Merits of plant introduction :

 Plant introduction offers following advantages-

(i) It provides entirely new crop plants.

(ii) It provides superior varieties either directly, after selection or through hybridisation.

(iii) Introduction and exploration are the only feasible means of collecting germ plasm and to protect viability from genetic erosion.

(iv) It is very quick and economic method of crop improvement, particularly when the introductions are released as varies either directly or after selection.

(v) Crop species may be introduced in new disease free areas to protect them from damage. E.g. Coffee and Rubber.

(vi) This method is applicable in all self pollinated, cross pollinated and vegetative propagated crops.

Demerits of plant introduction :-

Some of the demerits of plant introduction are as follows-

(i) Argimone mexicana, Eichhornia crassipes, Phylaris minor are some some of the weeds that entered India along with plant introductions.

(ii) Late bright of potato from Europe, Flag smut of wheat from Austrelia, Coffee rust and brunch top of banana arrived from Ceylon etc. have been introduce in India.

(iii) Some introduced ornamental species may become noxious weeds in the new habitat, as for example Lantana camara in India.

(iv) Some introduced species may disturb the ecological balance in their new habitat and may cause serious damage to the ecosystem. For example Eucalyptus introduced from Australia cause a rapid depletion of the subsoil water reserves.

Acclimatisation :-

Acclimatisation refers to adaptation or adjustment of an introduced variety to the new environment. Generally the introduced varieties performed poorly, because they are often not adapted to the new environment. Sometimes the performance of a variety in the new environment improves with the number of generations grown there. The process that leads to the adaptation of a variety, line or population to a new environment is called acclimatisation.

It is brought about by aq faster multiplication of those genotypes that are better adapted to the new environment. The extent of acclimatisation is determined by

(i) mode of the pollination

(ii) magnitude of genetic variability present in the original population

(iii) the duration of the life cycle of the crop.

(iv) mutation.