Aromatic Tagetes plants produce secondary products which have a biological
activity against a wide range of micro-organisms, insects and nematodes. Ta
getes oils are also used as pharmaceuticals and as flavour components in th
e food industry. This study aimed to use somaclonal variation to select dro
ught tolerant plants of Tagetes. Cotyledons cultured on MS medium containin
g 3 mg 1(-1) IAA and 10 mg 1(-1) BA (callus growth medium; CGM) with 60 mM
mannitol died. Shoot clumps developed on CGM for 6 months and then subcultu
red onto CGM containing 80 mM mannitol also died. Four shoots were regenera
ted from 72 shoot clumps on 1/2 MS medium containing 0.5 mg 1(-1) IAA (shoo
t growth medium; SGM) after culturing on CGM without mannitol for 6 months
and then on CGM with 60 mM mannitol for 3 months. Twelve shoots developed f
rom 72 shoot clumps on SGM after culture for 9 months on CGM. Significant v
ariations were observed in biomass amongst regenerated clones when cultured
on medium containing mannitol. After growth in greenhouse conditions for 2
months, one clone developed from shoot clumps selected on medium with mann
itol exhibited a significant tolerance in vitro in medium containing 90 mM
mannitol: this medium completely inhibited growth of control plants. This c
lone had significantly higher proline content and soluble sugars than the n
on-stress-selected clone when cultured on medium containing 0 or 30 mM mann
itol. When tested for drought tolerance (growth at 40% soil field capacity)
in the greenhouse for 2 months, this clone showed a significant tolerance
compared with other regenerated and control plants and revealed lower water
potential, greater accumulated biomass and a higher relative growth rate.
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