Low thidiazuron levels promote and sustain shootlet multiplication in sugarcane

Effect of thidiazuron (N-phenyl-N′-1,2,3-thidiazol-5-ylurea; TDZ) was examined on multiplication of shootlet cultures established from buds regenerated from apical domes of sugarcane var. CoH-92 and Co-7717. A set of two shootlets taken from these cultures was inoculated on media containing varying levels of TDZ. The number of multiple shootlets formed provided a simple, quantitative test system. TDZ concentrations, as low as 10⁻⁹ M and 10⁻⁷ M, produced the highest number of shootlets in var. CoH-92 and Co-7717, respectively. These levels were up to 2×10⁻⁴ times lower than the other growth regulators tested. Greater multiplication of shootlets continued even after subculture on a medium devoid of TDZ for 24 and 48 days. This is suggestive of a high persistence of TDZ in the tissues. Cytokinin-like effects of TDZ at such low concentrations are uncommon and sustained effects of low concentrations, as in this response, unreported. Multiple advantages of TDZ in micropropagation of sugarcane are discussed.