Improvements in Cereal Tissue Culture by Thidiazuron: A Review

This article reviews research to establish highly regenerative cell and tissue culture systems in cereals and grasses as a prerequisite for crop improvement using biotechnological methods. The strategies were described in the historical framework of investigations in this field and then new approaches were discussed focussing on the considerable recent progress made using the cotton defoliant thidiazuron (TDZ) for enhancement of morphogenic competence in the Poaceae during the last 15 years. In 1982, TDZ was first described to have cytokinin-like activity and subsequently, numerous studies have characterized this compound as a powerful plant growth regulator for dicots with special emphasis on recalcitrant leguminous and woody species. However, TDZ was evaluated for cereal tissue culture with a remarkable delay. The results summarized clearly showed that TDZ can significantly improve morphogenic response from callus derived from a wide range of explants concerning frequency of shoot formation, number of shoots per explant and the time needed for shoot induction compared to other cytokinins. Moreover, TDZ has been used effectively for establishment of shoot meristematic cultures from model and agronomically important cultivars using shoot apices, shoot meristematic segments as well as nodes and pronounced differences were obtained regarding shortening of the time frame especially for barley and wheat. Besides that, high frequency plant regeneration with long-term retention of morphogenecity in a relatively genotype-independent manner was observed. Nevertheless, in a few cases problems associated with the use of TDZ were noted. The data summarized imply that TDZ is also a potent growth regulator fo