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Effects of Picloram and Other Auxins on Onion Tissue Cultures


Seedling shoot meristem-tip explants of ‘Yellow Grano’ and ‘Yellow Sweet Spanish’ onions (Allium cepa L.) were cultured in vitro on media varying in auxin and cytokinin composition. 4-Amino-3,5,6-trichloropicolinic acid (picloram) as an auxin source was superior to α-naphthaleneacetic acid (NAA) used as a control for shoot multiplication cultures maintained for 6 months or longer. A combination of 0.03 mg/liter picloram and 0.5 mg/liter 6-benzylamino purine (BA) was optimal. Picloram was comparable or superior to the 2,4-dichlorophenoxyacetic acid (2,4-D) control for induction, continued maintenance and friability of callus, and subsequent regeneration of plants. Somatic embryos developed at high frequency in some lines of both cultivars on media containing 0.75 mg/liter picloram and 1.5 to 2.0 mg/liter BA. The most promising scheme for plant regeneration from 6- to 12-month-old callus cultures involved transfer from somatic embryo induction media to modified shoot multiplication media. These techniques also were successful using mature bulb basal plate-scale explants.