SOMACLONAL VARIATION IN GROWTH, LEAF PHENOTYPE AND GAS-EXCHANGE CHARACTERISTICS OF POPLAR - UTILIZATION OF LEAF MORPHOTYPE ANALYSIS AS A BASIS FOR SELECTION

Populus hybrid TT32 lines produced from 15 treatment tissue culture re gimes exhibited somaclonal variation in morphological and gas exchange parameters. Within four years of regeneration, discrete lines showing statistically validated superior, or inferior, growth performance rel ative to the parental reference clone were identified. Significant dif ferences in the ratio of leaf length/width between treatment lines pro vided the earliest reliable indicator of the divergence in overall gro wth performance. Despite discernible variation in leaf phenotype among primary regenerants and secondary propagules within individual lines, the leaf length/width ratio was identified as a potential parameter f or predicting growth performance. Its subsequent use led to the recogn ition of four distinct leaf morphotypes; cordate, ovate. reniform and oval. Two or more of these morphotypes were distributed within each of the original 15 treatment lines. Regrouping the data on the basis of leaf morphotype resulted in a clear segregation of the morphological t raits, and revealed differences that were not readily apparent by stat istical analysis based on treatment groups. The demonstration of simil ar relative performances by individual morphotypes with respect to a r ange of growth and gas exchange parameters confirmed that variation in leaf morphology was indicative of differential photosynthetic perform ance. Somaclonal variants with a leaf morphotype closest to that of th e parental line showed the highest overall potential for selection, su ggesting that the greatest benefits accrue from a minimal disturbance of the parental leaf phenotype.