Abstract

Production of new genetic variability to improve the existing clones to withstand and overcome new adverse environmental factors and emerging pest and disease problems are essential for success of a clonal forestry programme. This is particularly so in the case of selection of clones for disease resistence. Pathogens causing diseases are evolving constantly and rapidly because of short generation periodin contrast, trees have got a prolonged generation period. Hence, occurence of genetic variation in microorganisms are at a much faster rate than in trees. Therefore, in a race between virulence of the pathogen and resistance of the host, the pathogen will have an upper hand, and gradually it subjugates the host. hence, unless genetic improvement of clones is undertaken continuously creating more and more genetic variability in the population for further selection of improved genotypes, the advantage of clonal forestry will come down gradually