Hecht, M., Department of Ornamental Horticulture, The Volcani Center, P.O. Box 6, Bet Dagan, #50-250, Israel
Ecker, R., Department of Ornamental Horticulture, The Volcani Center, P.O. Box 6, Bet Dagan, #50-250, Israel
Ran, S., Department of Ornamental Horticulture, The Volcani Center, P.O. Box 6, Bet Dagan, #50-250, Israel
Watad, A.A., Department of Ornamental Horticulture, The Volcani Center, P.O. Box 6, Bet Dagan, #50-250, Israel

The responses of two lisianthus (Eustoma grandiflorum) inbred lines and their heterotic (in vivo) F1 hybrid to different levels of benzyladenine (BA) and gibberellic acid (GA3) were studied under in vitro conditions. Number of axillary shoots developed (NAS), main shoot length (MSL), total fresh and dry weights, and extent of callus formation were measured. The two parents differed in their response to both hormones by all parameters measured. High-parent heterosis for NAS and MSL proved to be dependent on the specific BA and GA3 levels. The required BA concentrations for maximum NAS and MSL for the F1 were higher than those required for either parent; this may be defined as a heterosis in BA-requirement for maximal in vitro response. Adding 0.25 or 1 mg/liter GA3 to the medium caused a considerable increase in NAS and in dry weight gain only when combined with BA. On the other hand, MSL was increased by GA3 addition only at 0 or 0.1 mg/liter BA, but not at 0.5 mg/liter BA. Callus formation was greatly encouraged by raising the BA level from 0 to 0.1 or 0.5 mg/liter and by the addition of GA3 at low BA level. Assumed differences in endogenous BA and GA levels among the genotypes studied seemed to be related to the expression of heterosis. © 1994 Society for In Vitro Biology.