Genome Analysis of Populus Species: Assessment of Genetic Diversity of P. deltoides, Characterization of Wide Hybrids and Phylogenetic Analysis using Molecular Markers.

摘要

The species Populus ciliata, the only native poplar of India, is endemic to the Himalayan belt and has been an important tree for the forest breeders of India. Around 1950, a large number of exotic clones of Populus were introduced and grown in North India. Thus the study of poplars becomes essential to complement to the ever increasing knowledge database of this important tree species.;Reliable identification of diverse germplasm within a given species is required for development of intra-specific hybrids for germplasm improvement. P. deltoides is an important exotic species having a widespread distribution and is a valuable timber tree. It is grown as one of the best exotic clones by most of the poplar breeders in India and several hybrids have been developed from it. The cataloging of the level of genetic diversity of this species thus becomes essential for producing hybrids with heterotic vigor. Study of genetic diversity in different P. deltoides accessions collected from all over the world using DNA based markers forms a part of the present research.;Micropropagation technique has been employed for rapid multiplication of the widely planted fast-growing Populus species. Complete clonal uniformity is desirable among the in-vitro raised plants. Variations do occur in the tissue culture derived plants which are termed as somaclonal variations. Any variation is a matter of concern as clonal fidelity is the pre-requisite of the entire exercise of micropropagation. Testing the genetic integrity of the in-vitro raised plants of P. deltoides with the help of molecular markers has been undertaken in the present research work.;Development of hybrids, inter-specific and intra-specific, have always been carried out by breeders to exploit the occurrence of heterosis, i. e. the hybrids show characteristics which are better than both of the parents. Poplar inter-specific hybrids have been known to show extremely rapid growth and are of increasing importance for tree improvement programs. Poplar hybrids (Populus spp.) are a result of natural and manmade crosses among poplar species. Hybrid poplars are suitable for a number of uses including pulp, lumber and plywood, fuel, conservation, and ornamental plantings. Compelling reasons for planting hybrid poplars include rapid growth and ease of vegetative propagation from stem cuttings. On good sites, hybrid poplars grow faster than any other northern temperate region tree and harvests can be made much sooner in the hybrids.;The hybrids developed in Populus are identified mainly on the basis of morphology. It is difficult to characterize the hybrids based on the phenotypic (morphological) markers at the early stage of development. Also all hybrids being developed are not necessarily true hybrids and require precise identification for further breeding and selection. The fast growing P. ciliata × maximowiczii hybrids developed in India are known to outperform their parents in terms of growth performance and yield. DNA based molecular markers can serve as powerful tools for reliable identification of such hybrids as they are capable of identifying true hybrids at a very early (seedling) stage of development. A study using molecular marker systems would help in identification of true hybrids at early stage; and if a marker can be associated with growth performance, selection of better clones would become very convenient. The present research uses molecular marker technique for testing the hybridity of the P. ciliata × maximowiczii hybrids.;Retrotransposons form a major portion of the genome, especially in plants. It may be up to 70% to 80% of the whole genome, and are dispersed throughout the chromosomes. Their ubiquity and universal presence makes them ideal choice to target as molecular markers. Development of a strategy for retrotransposon based fingerprinting in poplars has been undertaken in the present research work. Addition of new markers is always an advantage as they offer more coverage of the genome. Hence, the research to develop a novel marker system for poplar genome becomes all the more interesting.;The 30 (and more) species of the genus Populus have been classified into different sections with a doubtful taxonomic placement of the species P. euphratica. However, P. euphratica is a very important tree as it is a hardy species that grows very well even in adverse environments such as drought and salinity. The species P. euphratica is morphologically very distinct from the rest of the species of the genera and several workers challenge its taxonomic position. Considering the potential implication of repetitive DNA elements for molecular phylogeny, the present work includes isolation and characterization of repetitive DNA elements especially 5S rDNA from the species P. euphratica. (Abstract shortened by UMI.).