Effects of thidiazuron, ethylene, abscisic acid and dark storage on leaf yellowing and rooting of Pelargonium cuttings

The effects of post-harvest treatments with thidiazuron (TDZ), ethylene and abscisic acid (ABA), and dark storage of Pelargonium cuttings were investigated. TDZ-treatment markedly delayed the onset of leaf senescence in cultivars 'Fire', 'Katinka' and 'Ganymed'. Storing the cuttings in the dark for 4 d and/or treating them with 2 mu l l(-1) ethylene or 100 mu M ABA hastened the onset of leaf yellowing, while 5 mu M TDZ retarded leaf yellowing. TDZ maintained leaf chroma values because TDZ-treated leaves remained green. In contrast, applying ethylene, ABA or dark storage increased leaf chroma because the leaves turned yellow. TDZ-treated leaves had high chlorophyll contents, while levels declined in the untreated controls. Ethylene at 2 mu l l(-1) increased the rooting proportions (%) in all cultivars, but reduced the numbers of roots per cutting and root lengths. Short-term dark storage and 100 mu M ABA reduced the ability of cuttings to continue growth of regenerated roots. This effect was evidenced as reduced numbers of roots per cutting and root length. Applying 4 mu l l(-1) indole-3-butyric acid (IBA) in the nutrient solution induced the maximum proportion of cuttings to root in cv. 'Ganymed', increased the numbers and lengths of roots, and offset the inhibitory effect of TDZ on root formation. Leaf yellowing in Pelargonium cuttings was due to stress-induced ethylene after dark storage, or to ABA-treatment. However, TDZ-treatment was able to antagonise their deleterious effects with the concomitant beneficial effect of delaying the onset of senescence.