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Twenty one full-sib families derived from intra- and interspecific controlled crosses were analysed to study different genetic parameters. Estimates of the general combining ability (GCA) variance were found to be less than the specific combining ability (SCA) variance for all the parameters. The dominance variance was more than the additive variance for all the parameters studied. The degree of dominance ranged between 1.73 (per cent successful crosses) and 5.35 (% germination). Moderately high (0.42 for % successful crosses) to low (0.15 for seed per capsule) narrow sense heritibilities and high heritability in broad sense (0.74 to 0.99) for per cent successful crosses and seeds per catkin was recorded. GCA effects were positive and significant for S. tetrasperma (TFB), S. tetrasperma (TWE) and S. tetrasperma (LNM) male parents for all the parameters while S. alba (SE- 63–007) exhibited significantly positive effects for number of seeds/catkin. Among females, S. tetrasperma (LP), S. tetrasperma (LNF) and S. tetrasperma (LN) depicted positive and significant GCA effects for number of seeds/catkin and per cent germination, respectively whereas crosses, S. matsudana (PN-227) x S. alba (Kashmiri) and S. tetrasperma (LNF) x S. tetrasperma (LNM) exhibited positive and significant SCA effects for per cent successful crosses. Cross S. matsudana (PN-227) x S. alba (Kashmiri) showed positive significant SCA effects for number of seeds/capsule.

Exploitation of genetic variability of Populus deltoides Bartr. through control crossing involving Line x Tester mating design was attempted with the objective of selection of suitable clones as well as parents for hybridization in future and identification of best families and best individuals with in family for releasing first stage clones. Lines ST-72, D-121, G-48, exhibited the highest positive GCA effects for plant height, collar diameter, plant height at first branch and root length. In general G-48 also proved to be the best combiner for survival percentage, inter nodal length and leaf area. Among the testers ST-63 and ST-70 expressed highest GCA effects and excelled for a number of desirable characters. Full sib families (F1s) of D-121 x ST-70 and G-48 x ST-63 showed desirable SCA for plant height and collar diameter and therefore F1 hybrids of these crosses are recommended at first stage of selections. The percent contribution of line x tester interactions was higher than that of lines and testers except number of leaves per plant. 13 traits expressed higher SCA variance than GCA variance and dominant gene effect (σ2D) were found higher than additive gene effect (σ2A) except in root length. For recurrent selection based on GCA effects, parents G-48, ST-70, D-121 and ST-63 appeared more appropriate in crossing programme directed towards clonal improvement of Poplar in India.

Eighteen selected clones of Salix were taken to study genotype x environment interaction. Significant differences were observed for genotype, environments and genotype x environment interaction except non-significant genotype x environment interaction for plant height increments. Stability analysis revealed that the most of the genotypes were responsive to environmental changes. The Salix clones exhibited maximum growth in 2007 and 2010 growth years. Based on phenotypic indices (Pi), regression coefficient (bi) and deviation from regression (S2di) the clones J-799, SI-63-007 and NZ-1002 for volume index and SI-63-007 for diameter at breast height were found most adaptive to overall environments. Suitable clones for poor environment was J-194, while for average environments were V-99, NZ-1040 and NZ-1179, respectively for diameter at breast height. Clones suitable for rich environment are PN7-31 for diameter at breast height and NZ-1140 and 131/25 for volume index. The clones identified for different agro ecological regions must be chosen by considering stability of the clones towards that environment.

Results on crossability among diffent species revealed higher compatibility rate for intra-specific crosses of Salix tetrasperma and S. matsudana as compared to inter-specific crosses. Crossing of different species within sub-genus Salix and among section were possible, whereas crossing of species between sub-genus Salix and Vetrix did not yield viable seed. S. tetrasperma from section Humboldtianae successfully crossed with members belonging to section Salix, Subalbae and Nigrae. S. babylonica of section Subalbae successfully crossed with member of section Humboldtianae and Salix. Maximum percentage (78.24%) of successful crosses was recorded for intra-specific crosses involving S. matsudana (PN-227) and S. matsudana (PN-722). Among inter-specific crosses, percentage successful crosses varied between 42.86 per cent for S. matsudana (PN-227) x S. alba (SI-63-007) and 7.50 per cent for S. tetrasperma (LNF) x S. alba (SI-63-007). Maximum germination percentage (78.00 per cent) among interspecific hybrids was recorded for S. matsudana (PN-227) x S. alba (SI-63-007), whereas minimum (26.00 per cent) was registered for S. babylonica (FB) x S. tetrasperma (TFB). The RAPD fragments obtained after PCR amplification of ybrid [(S. tetrasperma (LG) x S. tetrasperma (TWE)] recorded 100 per cent and 70 per cent similarity with male and female parent respectively. Maximum similarity (96%) with female parent was recorded in S. matsudana (PN-227) x S. matsudana (PN-722) suggesting dominating control of female parent.