THAKUR, SANJEEVTHAKUR, SHIKHA2018-01-192018-01-192017-12http://krishikosh.egranth.ac.in/handle/1/5810039640ABSTRACT The present investigation entitled “Association genetics in Populus deltoides” was carried out in the Department of Tree Improvement and Genetic Resources, Dr Y. S. Parmar University of Horticulture & Forestry Nauni, Solan (HP) during 2013-2016. There is a collection of Populus deltoides clones procured from different countries namely USA, Australia and parts of India and maintained in the germplasm block of Naganji nursery from which ninety five clones were included in the study. Cuttings were raised in the nursery in RBD with three replications at 50 cm X 50 cm spacing and were evaluated for morphological characters in field as well as wood and molecular studies in laboratory. Analysis of variance revealed that all morphological traits were significantly different in nature. On the basis of clustering of morphological and wood traits, ninety five clones were distributed into five distinct clusters suggesting the presence of different sources of relationships amongst the clones. The gene action study revealed that additive variance was observed more than the dominance variance for most of the parameters studied except for growth traits. Growth traits expressed highly significant and positive genotypic as well as phenotypic correlation. Ninety five clones were tested for their genetic diversity using hundred SSR markers out of which ninety three gave results and sixteen ISSR markers out of which ten markers gave results. Results disclosed that dendrogram generated from ninety three SSR markers divided whole population of ninety five clones into two major clusters whereas dendrogram generated from ISSR markers depicted that whole population was divided into three major clusters. The structure analysis from SSR data revealed that the population gets divided into two sub-populations whereas from ISSR data, it was clear that the population gets divided into three sub-populations indicating the level of diversity existing in the population. On the basis of population structure analysis it is concluded that this clonal population structure is diverse. Results from genetic diversity analysis as well as STRUCUTRE analysis showed that the clustering pattern of the genotypes in STRUCUTRE analysis were almost similar to the splitting in the UPGMA tree which reveals that all the genotypes were clustered better with two clusters in SSR markers and three clusters in case of ISSR markers. Association studies of commercially important wood traits were conducted using ISSR and SSR marker data. Some important associations of markers with specific gravity of poplar wood were found in case of SSR markers whereas with ISSR markers, various associations of holocellulose and lignin content were obtained.ennullThesis