Genetic diversity-maintenance of cross pollinated germplasm -A review

Bio-diversity will help not only in increasing agricultural productivity but also in developing disease resistant varieties. It was evident in the early 1970’s when an epidemic called grassy stunt, virus destroyed more than 1,60,000 hectares of rice in Asia. A wider genetic base is essential and its accumulation assumes priority in agricultural research aimed at breeding new varieties/hybrids to raise production and productivity. This diversity is composed of native land races, local collections, elite cultivars and a wide variety of wild relatives of crop plants. As favourable alleles are selected and fixed, genetic variability is reduced, thus presumably reducing the potential for future progress. Finally, breeder want to collect enough material, increase, use and storage. Cross pollinated species can be increased by inter crossing, selfing or pooling. Storage of seed in a favourable environment is the most efficient method for preserving plant germplasm. Seed germplasm should be stored in an environment that will maximise its longevity. Characteristics measured should be those used in the genetic improvement of the species in question. Strategies for introgression depend on the reproductive biology and genetics of each crop and the available exotic germplasm. In wheat, amphihexaploid (synthetic) constructed from crosses between durum or other AB genome tetraploid and T. tauschii (D. genome diploid) are useful genotypes for introgressing exotic germplasm because of the crossing and selection. The decentralized breeding programme should help to inject into world agriculture a wide range of genetically diverse variet!es constituting a multiple complex and erecting genetic barriers against the build up and spread of pest and pathogens.