Watad, A.A., Dept. of Ornamental Horticulture, ARO, Volcani Ctr., Bet D., Rehovot 76100, Israel
Luria, G., Kennedy-Leigh Ctr. for Hort. Res., Fac. Agric., Hebrew Univ. J., Rehovot 76100, Israel
Borochov, A., Kennedy-Leigh Ctr. for Hort. Res., Fac. Agric., Hebrew Univ. J., Rehovot 76100, Israel

Aconitum (Aconitum napellus) is a hardy geophytic herbaceous perennial, with a tall leafy stem bearing violet or blue flowers on long, packed racemes. Although aconitum was introduced as a new commercial cut-flower crop almost 20 years ago, it is produced on a rather limited scale, because of low flowering percentages and low flower quality. The aim of this work was to study the factors responsible for these drawbacks. Growth curves of the different organs showed that daughter tubers reach their final weight ca. 4-6 weeks after flowering, when the tuber's central bud starts to elongate. At this stage, there is no flower differentiation. Flowering was highly dependent on tuber weight: 30- to 40 g tubers gave flowers of optimal quality, whereas plants derived from tubers of 5 g or less did not flower. Plants from larger tubers produced more tubers, whereas smaller ones had a higher growth rate. Treating the tubers with 200 ppm GA3 enhanced sprouting of dormant tubers. Plants did not develop from tubers at 27°C or higher, whereas at 22°C or below the tubers sprouted and developed vigorous plants. Long-day conditions, begun when plants were 10 cm high and continued until harvest, increased plant height and flower quality spraying 10 cm plants once with 100 ppm GA3 resulted in enhanced stem and raceme elongation. Failure to flower resulted from both internal and environmental factors: small tuber size, limited solar radiation and small root-system volumes resulted in low flowering percentages.