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 Eucalyptus microtheca (37, 42 and 43) were grown in vitro under saline conditions (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 that of Clones 37 and 42. Leaf growth, expressed as leaf length, was stimulated 40% in Clone 42 and 33% in Clone 43, but was progressively inhibited 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 increased, and this was correlated with inhibition of growth. Because of 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 grown in the presence of 140 mM NaCl. The development of techniques for selecting seedlings by monitoring the physiology of shoots in vitro instead of testing whole plants in vivo will provide a relatively simple method of selection for woody trees.