Question

Explain mass selection and pure selection. How is pure line selection a better method for crop improvement?

Answer 1

As the name commences mass means big and bulk selection, where as pure means one varied selection. Hence mass selection is done for the bulk of the population of plants and the pure selection refers to the small and varied characters.

Complete answer:
Mass selection is the method of crop improvement used in plant breeding. It is commonly used for self-pollinated plants as well as for the cross-pollinated plants. A major population of plants are selected in this method. The plants are chosen on the basis of their phenotype and performance for the breeding.
Pure selection refers to the selection of a pure line of organisms with the desired characteristics. Plants are usually selected for not having similar phenotypic characters. The plants selected are subjected to the progeny test. It is commonly used for self-pollinated plants.
Pure-line selection is better for crop improvement due to following reasons:

The new variety formed is a pure line which is highly uniform, genetic variation minimal.
Pure line variety has a narrower adaptation and hence variety is easily identified in seed.
The improvement of crop variety is the best which is present within the existing variety of population. Hence this selection provides the best improvement over the original one.

Note:
Mass selection is a mixture of pure lines and hence has more genetic variation and is less uniform. The variety is inferior to the pure lines.
Pure lines usually involve selection from superior organisms for a number of generations until a pure line of organisms with desired characters has been formed.