Hybrids of Populus ciliata x maximowiczii are very vigorous and outperform both the parents in growth performance and yield. Genetic evaluation of 24 of these interspecific hybrids along with the two mother trees ( Populus ciliata), and five male-parent ( Populus maximowiczii) genotypes was carried out using the AFLP marker assay. Eight AFLP primer combinations detected 428 markers, of which 280 (66%) were polymorphic. Genetic relationships within the samples were evaluated by generating the similarity matrix based on Jaccard's coefficient. The phenetic dendrograms, as well as the PCO plots, separated the hybrids and the two parent species into three distinct clusters. The hybrids grouped closer to the P. ciliata (female parent) cluster as compared to the P. maximowiczii (male parent) cluster. The hybrid cluster contained internal groupings, which correlated to some extent with growth performance. The four best performing hybrids (42m1, 65m1, 23m2, Cm2-5-20/91) formed a distinct sub-cluster. Data from a single primer combination was sufficient for distinguishing the hybrids from the parents and assigning paternity. The hybrids showed 22 markers that were absent in P. ciliata but were monomorphically present in all the hybrids, suggesting outcrossing and common paternity. Further, these 22 markers were found in all the P. maximowiczii genotypes confirming it as the male parent. These male-specific markers can be converted to SCAR markers and used for rapid screening of the P.ciliata x maximowiczii hybrids. The primer combination E-AAC x M-CAA was identified as most suitable for ascertaining true hybridity. AFLP proves to be a useful tool for screening of P. ciliata x maximowiczii hybrids at the early stages of development.

No abstract

This report aims to describe the identification and molecular characterization of a 145-bp tandem repeat family that accounts for nearly 1.5% of the Populus genome. Three members of this repeat family were cloned and sequenced from Populus deltoides and P. ciliata. The dimers of the repeat were sequenced in order to confirm the head-to-tail organization of the repeat. Hybridization-based analysis using the 145-bp tandem repeat as a probe on genomic DNA gave rise to ladder patterns which were identified to be a result of methylation and (or) sequence heterogeneity. Analysis of the methylation pattern of the repeat family using methylation-sensitive isoschizomers revealed variable methylation of the C residues and lack of methylation of the A residues. Sequence comparisons between the monomers revealed a high degree of sequence divergence that ranged between 6% and 11% in P. deltoides and between 4.2% and 8.3% in P. ciliata. This indicated the presence of sub-families within the 145-bp tandem family of repeats. Divergence was mainly due to the accumulation of point mutations and was concentrated in the central region of the repeat. The 145-bp tandem repeat family did not show significant homology to known tandem repeats from plants. A short stretch of 36 bp was found to show homology of 66.7% to a centromeric repeat from Chironomus plumosus. Dot-blot analysis and Southern hybridization data revealed the presence of the repeat family in 13 of the 14 Populus species examined. The absence of the 145-bp repeat from P. euphratica suggested that this species is relatively distant from other members of the genus, which correlates with taxonomic classifications. The widespread occurrence of the tandem family in the genus indicated that this family may be of ancient origin.

Clonal variation in morphological growth parameters of Populus deltoides and P. ciliata were studied in the nursery stages in Sub-tropical (Naganji) and Sub-temperate (Shilli) regions to assess their planting success and growth potential in their climatic zones. P. deltoides clones planted in Sub-tropical nursery recorded highest average height (298.70cm), basal diameter (21.75mm) and leaf area (175.40cm2) with clone ‘PD-1’ sharing maximum height (350.00± 26.07cm) and leaf area (193.70±6.86cm2). Whereas, basal diameter was recorded maximum in the clone ‘G-48’ (25.05±3.77mm). Among P. ciliata clones planted under Sub-temperate condition clone ‘Chhachpur’ recorded maximum height (159.00±24.54 cm) and leaf area (104.25±26.40 cm2) growth, whereas, basal diameter of 12.48±0.55 mm was found maximum in P. deltoides clone ‘90-2’. Standing fresh leaf biomass significantly decreased with advancement in month. Dry leaf biomass increased significantly from September to October. While, significant variation between sites having maximum fresh as well as dry leaf biomass was observed in sub-tropical nursery. It was observed that average height, diameter, leaf area and leaf biomass were almost double in the clones at Sub-tropical (Naganji) nursery as compared to Sub-temperate (Shilli).

The present investigation was carried out to study the growth behavior of Poplar clones under short rotation and intensive culture. Diameter increase of clones showed typical sigmoidal growth curve. Decline and irregular increase and decrease in c.a.i are mainly attributed to the flooding of area. However genetic constitution of individual clone is responsible for variation in growth rate of clones under investigation.