Assessment of Genetic Diversity in Crop Plants - An Overview

Abstract

Crop plant evolution either natural or human-directed, is primarily based on existing genetic diversity in the population. Diversity can be described as the degree of differentiation between or within species. Existing intra- and inter-specific differences are at the base of all crop improvement programmes. If all the individuals within the species would have been similar, then possibly there could not have been any scope for improvement in plant performances for different traits. Since the beginning of systematic plant breeding, natural variability and divergence between crops have been extensively identified and used in improvement of crop species. However, with the progress of time, natural variability got depleted due to (i) lopsided breeding practices focusing on improvement of only few traits (like yield and its component traits), (ii) frequent use of few selected genotypes as parents in varietal development programme and (iii) introduction of few outstanding lines to many countries thereby leading to increased genetic similarity between modern crop cultivars. Reduced genetic variability and diversity among crop plant species has raised serious concern among agricultural workers. With reduced genetic diversity, further improvement in crop varieties will be an arduous task. Breaking yield barriers will become difficult and plant breeders will be unable to meet the requirements arising out of ever-increasing demand on account of exploding population. Genetic diversity becomes more important in context of climatic change and associated unforeseen events as it may serve as the reservoir of many novel traits conferring tolerance to different biotic and abiotic stresses. Genetic diversity is the underlying cause of many important agriculturally important phenomena like heterosis and transgressive segregation. Diverse lines are needed for defect correction of commercial varieties and development of novel varieties. Hence, identification of diverse lines (if available), creation of diversity (if not available or limited) and its subsequent utilization are the major goals of any crop improvement programmes. In this context, knowledge on all aspects of genetic diversity viz., factors affecting genetic diversity, different methods of diversity analysis, their measurement and the softwares for carrying statistical analysis becomes imperative in order to utilize them prudently. Many reviews have been written focusing on vital issues like changes in genetic diversity under plant breeding,1 genetic vulnerability of modern crop cultivars,2 conservation and utilization of genetic resources3,4 assessment of genetic diversity using molecular markers5 and measurement of genetic diversity using statistical tools.6–8 In the present review, an attempt is being made for comprehensive compilation of overall concepts in the area of genetic diversity, which could be of immense significance for extending knowledge and meaningful research.