Adventitious rooting, a key step in clonal propagation is affected by tree maturation. Micropropagation followed by microcuttings propagation has the potential to rejuvenate the clones thereby enhancing the rooting potential and minimize intra clonal variation. In this study, 33 superior performing Eucalyptus camaldulensis clones were propagated by rooting of stem cuttings (SCs) and micropropagation. Micropropagated plantlets were used as stock plants for microcutting propagation. Rooting of SCs and micropropagation was carried out with the coppice shoot cuttings and axillary buds respectively, obtained from approximately fourteen year old trees that had undergone one vegetative propagation cycle. The adventitious rooting recorded was significantly higher in micropropagation (24.8-100 %) and microcuttings (43-95 %) than SCs method (9.3-75.5 %). Studies on ontogeny of adventitious rooting showed the emergence of root primordium from the phloem region and root initials were noticed within 5-9 days after auxin treatment. Further, molecular marker analysis showed genetic uniformity except for two ramets, detected using inter simple sequence repeats (ISSR) markers and suitable corrective measures were taken to avoid entry of such plantlets for mass multiplication. This study demonstrates the importance of integration of micropropagation and microcuttings production for rejuvenation and mass multiplication. Although current rejuvenation and root induction treatments favored adventitious rooting, the basic mechanisms involved in rejuvenation and adventitious rooting need to be explored for hassle free industrial rooting process, consequently cost effective propagation.

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Eucalyptus is an important industrial species with tolerance to drought and salt stress. Genetic improvement activities including quantitative trait loci (QTL) mapping for pulping and adventitious rooting traits are in progress, but no information is available on the genomic regions on adaptive traits such as stomatal characteristics. In this study, an interspecific cross between Eucalyptus tereticornis and E. grandis was generated for the development of genetic map and QTL identification for stomatal traits. Simple sequence repeats (SSRs), inter-simple sequence repeats (ISSRs) and sequence related amplified polymorphism (SRAP)markers were used for genotyping the F1 individuals. Parent-specific geneticmaps (female, 1023.56 cM;male, 1049.64cM) and consensus map (1049.4 cM) were developed. QTL analysis was carried out to identify the chromosomal regions affecting stomatal density, area and pore length in adaxial and abaxial leaf surface. Seven QTLs were identified with phenotypic variation of 11.36 to 27.30% for stomatal density, area and pore length. Correlation of stomatal traits when combined with growth and wood properties would have greater implications for generation of stress tolerant eucalypt hybrids with higher productivity and adaptability.

The eucalypt species, and, show tolerance to drought and salinity conditions, respectively, and are widely cultivated in arid and semiarid regions of tropical countries. In this study, genetic linkage map was developed for interspecific cross × using pseudo-testcross strategy with simple sequence repeats (SSRs), intersimple sequence repeats (ISSRs), and sequence-related amplified polymorphism (SRAP) markers. The consensus genetic map comprised totally 283 markers with 84 SSRs, 94 ISSRs, and 105 SRAP markers on 11 linkage groups spanning 1163.4 cM genetic distance. Blasting the SSR sequences against sequences allowed an alignment of 64% and the average ratio of genetic-to-physical distance was 1.7 Mbp/cM, which strengths the evidence that high amount of synteny and colinearity exists among eucalypts genome. Blast searches also revealed that 37% of SSRs had homologies with genes, which could potentially be used in the variety of downstream applications including candidate gene polymorphism. Quantitative trait loci (QTL) analysis for adventitious rooting traits revealed six QTL for rooting percent and root length on five chromosomes with interval and composite interval mapping. All the QTL explained 12.0-14.7% of the phenotypic variance, showing the involvement of major effect QTL on adventitious rooting traits. Increasing the density of markers would facilitate the detection of more number of small-effect QTL and also underpinning the genes involved in rooting process.

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