EFFECTS OF PHYTOHORMONES AND DARK STORAGE ON POSTHARVEST QUALITY OF PELARGONIUM CUTTINGS

Abstract

Maintenance of the leaf green colour, capacity to initiate roots and continued growth of initiated roots are important quality attributes in Pelargonium cuttings. Leaf senescence is a common problem in Pelargonium and leads to high postharvest losses. Ethylene, abscisic acid (ABA) and darkness have been implicated in promoting senescence, while cytokinins retard it. The effects of post-harvest treatments with ethylene, Thidiazuron (TDZ), ABA or dark storage were investigated to determine a potential commercial approach for improving postharvest quality of Pelargonium cuttings. Experiments were conducted in a completely randomized design, with two replications. The data obtained were subjected to a single factor analysis of variance using Statistical Analysis System programme. Storing cuttings in the dark for 4 days and/or treating them with 2 µL/L ethylene or 100 µM ABA hastened the onset of visible leaf yellowing in ‘Fire’, ‘Ganymed’ and ‘Katinka’. Conversely, 5 µM TDZ markedly delayed the onset of leaf senescence in all the cultivars. Thidiazuron increased leaf hue values (greenness), while ethylene, ABA or dark storage decreased leaf hue (hastened yellowing). Exposing Pelargonium cuttings to ethylene reduced root fresh weight in ‘Katinka’, but had no effect on root dry weight and root water content. Storing Pelargonium cuttings for 4 days in the dark reduced root fresh weight, root dry weight and water content in ‘Katinka’, but this was not apparent in other cultivars. Applying, 100 µM ABA reduced root fresh weight, root dry weight and water content in all cultivars. Thidiazuron severely inhibited adventitious root formation in all cultivars. The inhibitory effect was overcome by inclusion of indole-3-butyric acid (IBA) in the nutrient solutions. Thidiazuron counteracted the deleterious effects of dark storage, ethylene and ABA by delaying the onset of leaf yellowing in Pelargonium cuttings during storage and/or shipment. Thidiazuron should be applied to Pelargonium cuttings as a postharvest treatment to prevent subsequent leaf yellowing. Cuttings should not be stored under darkness or water stress to prevent accumulation of ethylene and ABA. After TDZ treatment, transportation and storage, Pelargonium cuttings should be dipped in 4 µL/L IBA to induce root development and enhance quality.