RESPONSE OF CLONES OF EUCALYPTUS-MICROTHECA TO NACL IN-VITRO

We studied the response of nodal segments of Eucalyptus microtheca F.J . Muell. to salt stress in a tissue culture system. Three clones of Eu calyptus microtheca (37, 42 and 43) were grown in vitro under saline c onditions (0-140 mM NaCl) for three months. The survival of all three clones decreased with increasing concentrations of NaCl in the medium, but the presence of up to 70 mM NaCl stimulated rooting in Clones 37 and 42. Shoot elongation of Clone 43 was less affected by salt than th at of Clones 37 and 42. Leaf growth, expressed as leaf length, was sti mulated 40% in Clone 42 and 33% in Clone 43, but was progressively inh ibited up to 27% by 70 mM NaCl in Clone 37. Massive accumulation of Na + and Cl-occurred, especially in Clones 42 and 43 (4000 and 3000 mmol Na+ kg(DW)-1; respectively), as the salinity of the culture solution i ncreased, and this was correlated with inhibition of growth. Because o f a reduction in the accumulation of K+ with increasing salinity, the K+/Na+ ratio decreased from a control value of 4.5 to 0.14 in shoots g rown in the presence of 140 mM NaCl. The development of techniques for selecting seedlings by monitoring the physiology of shoots in vitro i nstead of testing whole plants in vivo will provide a relatively simpl e method of selection for woody trees.