A novel approach for efficient plant regeneration from long-term suspension culture of wheat.

Hexaploid wheat plants were easily regenerated from young embryo-derived callus for twelve genotypes tested. After a 2.5 years culture period, however, most of the callus cells lost their ability to regenerate into shoots, but not into roots.A novel approach was used to regenerate shoots from the long-term suspension cultured cells. In general, instead of selecting embryogenic callus as source material, this approach requires the inoculation of unselected callus into liquid medium followed by removing the free floating cell portion, selecting out non-root forming cell clumps from the root forming primary suspension culture, and growing the putative shoot-competent clumps in liquid medium with reduced auxin concentrations. We have successfully established shoot-competent wheat suspension cultures for cv. 'Mustang'. High (>80%) frequencies of plant regeneration were observed from plating of 2.5 year suspension cultures. The suspension cultures established by this approach have been utilized to select for heat tolerant variants and will be an ideal source material for protoplast culture and transformation studies. This approach can also be applied to other cereal crops which form roots easily but are unstable in maintaining long term regenerable cultures and which are not easily adaptable to suspension culture.