Differential expression in vitro of heterosis in lisianthus (Eustoma Grandiflorum) at various benzylandenine and gibberellic acid levels

Summary 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.