Screening the juvenile clones of eucalyptus tereticornis sm for water use efficiency

Eucalyptus tereticornis Sm is an exotic fast growing arborescent species, commercially planted as a source of paper pulp and timber. One of the objectives of clonal forestry programme is to obtain better return for a given investment and this can be achieved only by planting with suitable clones. Several clones of Eucalyptus tereticornis have been raised by ITC Bhadrachalam and IFGTB, Coimbatore but a clonal comparison for physiological traits have not been carried out. The major objective of the present work was to screen the juvenile clones of Eucalyptus tereticornis for the photosynthetic traits such as photosynthetic rate (Pn), stomatal conductance (gs), internal CO2 concentration (Ci) and rate of transpiration (E). The clones were also assessed for photosynthetic ratios such as intrinsic WUE, instantaneous WUE, intrinsic carboxylation efficiency and mesophyll efficiency in order to identify elite clones of Eucalyptus tereticornis for clonal forestry programmes and also for planting drier areas so as to reclaim the waste lands. The results showed a significant variability for the physiological parameters such as Pn, gs, E and Ci and the derived ratios such as intrinsic WUE, instantaneous WUE, intrinsic carboxylation efficiency and intrinsic mesophyll efficiency in the clones of Eucalytus tereticornis. Clones were categorized based on their photosynthetic efficiency and some clones such as Et 130, Et 242, Et 008 and Et 027 were identified as superior clones as they had efficient stomatal regulatory capacity combined with better carboxylation efficiency and are ideal planting stock especially for drier areas. The superior clones which are identified based on photosynthetic efficiency could be considered as choice materials for further tree breeding programmes.