It is one of the oldest procedures in which individual plants or group of plants are sorted out from mixed population, thus eliminating undesirable ones. Selection methods are of two types - mass selection and pure line selection.
In this method, plants are selected based on their desirable morphological characters (phenotype). Their seeds are composite or mixed and the progenies are grown in masses. They are not individually tested.
After repeated selection for about five to six years, selected seeds are multiplied and distributed to farmers. The only disadvantage of mass selection is that it is difficult to distinguish hereditary variation from environmental variation.
Pure line selection
A pure line is a collection of plants obtained as a result of repeated self-pollination from a single homozygous individual. Hence, a variety formed by this method shows more homozygosity with respect to all genes. One disadvantage is that new genotypes are never created by this method.
Genetic variability is essential for adaptations in different environmental and seasonal conditions.
Crops like sugarcane, potato, tea, banana and certain species of grasses are asexually propagated and produce very poor seeds. Based on their phenotypic appearance, the method of clonal selection is employed to select improved variety from a mixed population (clones). Selected plants are multiplied through vegetative propagation to give rise to a clone. The genotype of a clone remains unchanged for a long period of time.
India has several varieties of crops such as maize, tobacco, tomato, potato and brinjal which were introduced from countries such as America, China and Australia. Introduced varieties sometimes do not get adjusted easily with our local environment. It takes some time for these introduced crops to settle. Sometimes, it is essential to select suitable and desirable variety from the introduced plants. For example, a mung Phaseolus mungo variety was introduced from China but was not giving good yield and produced dull coloured seeds. From amongst the introduced mung crop, a plant suddenly produced large and bright coloured seeds. This aspect may be due to sudden mutation. This variant plant was selected and further subjected to inter or intra specific crosses with our native crop. In this way, new varieties were produced and released as newly developed mung variety. Such a mung No.1 variety is now being cultivated in Punjab.