Exogenous Applications of Benzyladenine and Gibberellic Acid Inhibit Lower-leaf Senescence of Geraniums during Propagation

Abstract

After postharvest shipping, the lower leaves of zonal geranium (Pelargonium ×hortorum) cuttings often turn chlorotic and necrotic during rooting in a propagation environment. Our objective was to quantify the efficacy of spray applications of the plant growth regulators (PGRs) benzyladenine (BA) and/or gibberellic acid (GA) at various stages in propagation to reduce lower-leaf senescence and evaluate effects on subsequent rooting. In Expt. 1, cuttings of ‘Patriot White’ geraniums were harvested and treated with BA (2.5 or 5.0 mg·L−1), BA + GA4+7 (2.5 or 5.0 mg·L−1 each), or GA3 (0.5 or 2.0 mg·L−1) either before or after a 2-day storage period simulating commercial shipping. Post-shipment application of all PGRs eliminated leaf yellowing compared with cuttings treated pre-shipment, but rooting was inhibited. In Expt. 2, the promotion of rooting from a rooting hormone preceding treatment with BA (1.25 to 5.0 mg·L−1), BA+GA4+7 (1.25 to 5.0 mg·L−1 each), or GA3 (0.25 to 2.0 mg·L−1) was evaluated on ‘Patriot White’ geranium cuttings after a 2-day simulated shipping. Applying rooting hormones increased the percentage of fully rooted cuttings treated with BA and/or GA from 16.4% to 51.8%. In Expt. 3, cuttings of different geranium cultivars from a commercial producer varied in susceptibility and suppression of leaf yellowing after BA + GA4+7 applications. We conclude that foliar applications of BA + GA4+7 can suppress lower-leaf senescence and rooting during propagation of some geranium cultivars, and the inhibition of rooting can be at least partially overcome with an application of rooting hormone.