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. 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. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.