Morphoregulatory role of thidiazuron: morphogenesis of root outgrowths in thidiazuron-treated geranium (Pelargonium x hortorum Bailey).

Root outgrowths formed on the root tissue of geranium (Pelargonium x hortorum Bailey cv. Kim and cv. Shone Helena) plants in response to treatment with the phenylurea derivative, thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5'-ylurea; TDZ). Treatment with the cytokinin N(6)-benzylaminopurine (BAP) or the auxin α-naphthaleneacetic acid (NAA) did not result in stimulation of similar abnormal structures on the root tissue. Significantly more outgrowths developed on roots of plants treated with 10 μM and 20 μM TDZ than on control plants or those treated with 1 μM TDZ for the eight-week treatment period. Some outgrowths produced shoots and plantlets while still attached to roots, and regenerants were easily separated from the root tissue and transferred to soil in the greenhouse where they grew to maturity. Histological observations suggested these outgrowths originated from the vascular cambium region of the root.