Division of Genetics, Indian Agricultural Research Institute, Delhi-12
*Paper based on a part of the data submitted to the Faculty of the Post Graduate School, I.A.R.I., New Delhi, in partial fulfilment of the requirements for the Ph.D. degree by P. L. N. SOMAYAJULU.
The genetic divergence among a set of 67 wheat strains chosen to represent a wide spectrum of phenotypic variation in respect of characters affecting yield has been estimated utilising the D2-statistic. The estimates were obtained under three different environments representing different levels of fertility. The number of clusters into which the 67 strains could be grouped differed somewhat from environment to environment and the composition of the clusters also varied. However, a closer study of the grouping revealed that such instability was restricted to only those clusters the divergence between which was quite low, whereas the widely divergent clusters remained distinct in all the experimental environments. In view of the consistency of this result, it may be inferred that the Mahalanobis D2-statistic can be a powerful tool in the hands of the breeder, as an estimator of genetic divergence among populations. Estimates of genetic divergence obtained in an environment conducive to a maximal expression of the genetic potential of the strains in respect of the various characters, may provide the most realistic picture with regard to genetic divergence.
Genetic diversity of a low order was observed among the 49 strains of Indian origin in spite of several factors such as the introduction and use of widely diverse exotic germ plasm in the breeding programme over a long period. Results of this study lead to the conclusion that selection towards uniformity in characters such as flowering time, plant height, ear and grain characters, ability to perform well under relatively low fertility environments, disease resistance, etc., can have a great depleting effect on genetic diversity.
