In vitro selection and characterisation of a drought tolerant clone of Tagetes minuta.

Aromatic Tagetes plants produce secondary products which have a biological activity against a wide range of micro-organisms, insects and nematodes. Tagetes oils are also used as pharmaceuticals and as flavour components in the food industry. This study aimed to use somaclonal variation to select drought tolerant plants of Tagetes. Cotyledons cultured on MS medium containing 3 mg l(-1) IAA and 10 mg l(-1) BA (callus growth medium; CGM) with 60 mM mannitol died. Shoot clumps developed on CGM for 6 months and then subcultured onto CGM containing 80 mM mannitol also died. Four shoots were regenerated from 72 shoot clumps on 12 MS medium containing 0.5 mg l(-1) IAA (shoot 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 from 72 shoot clumps on SGM after culture for 9 months on CGM. Significant variations 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 mannitol exhibited a significant tolerance in vitro in medium containing 90 mM mannitol; this medium completely inhibited growth of control plants. This clone had significantly higher proline content and soluble sugars than the non-stress-selected clone when cultured on medium containing 0 or 30 mM mannitol. 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.