Using Gibberellins to Prevent Leaf Yellowing in Cut Lilies

Hybrid lilies are excellent cut flowers due to the availability of flowers with various colors and shapes. Extensive inter-species hybridization has resulted in numerous cultivars, and many new cultivars are introduced to the market each year. While the vigor and reliability of the crop has improved over the years, what has not changed is that successful use depends on the postharvest quality of the cut stem.

The postharvest performance of cut lilies is dependent on many factors, such as the cultivar, preharvest conditions, stage of harvest, and postharvest environment and handling. Vase life of the cut stem usually ends when flower petals wilt or turn brown, but leaf quality is another important postharvest aspect. In many, if not most, hybrid lily cultivars, leaves start to turn yellow well before the end of the inflorescence life, making the stems less attractive. This is especially true if the stems have been cold-stored for any length of time prior to marketing. Generally, the vase life of cut lilies varies from 5-14 days, depending on the cultivar.

The potential use of growth regulators, especially gibberellins and cytokinins, has not been studied adequately in cut lilies. Our previous studies have shown that spray treatments with GA4+7 alone or in combination with BA (i.e., Fascination, Valent USA) remarkably reduce cold-induced leaf yellowing in pot hybrid lilies and gradual leaf yellowing in Easter lilies. We have also seen positive effects on flower longevity in these hormone-treated plants. These observations warranted the investigation of potential use of these chemicals in cut lilies.

This research was carried out to investigate the potential use of gibberellins and benzyladenine (BA) to improve postharvest quality of cut hybrid lilies. Experiments were conducted using various cultivars from different groups of hybrid lilies to test different aspects of treatment, such as the concentration, method of application and time of application. We want to emphasize that this is a research report and that the chemicals evaluated in this project are not currently labeled for use on cut lilies. Please contact your chemical representative before any new usage and always follow chemical labels.

Experiments

Experiments were conducted with a range of commercially important cultivars of Oriental, Asiatic and LA-hybrid lilies. Cultivars tested include Asiatics ‘Amarone’, ‘Colosseo’, ‘Marseille’, ‘Orandiso’, ‘Vermeer’ and ‘Vivaldi’; Orientals ‘Berlin’, ‘Helvetia’, ‘Muscadet’, ‘Tom Pouce’, ‘Star Gazer’ and ‘Sissi’; and LA-hybrids ‘Cebeco Dazzle’, ‘Fangio’, ‘Royal Parade’, ‘Royal Perfume’ and ‘Samor’. Plants were grown in Á bulb crates with MetroMix 360 in Cornell University greenhouses according to standard cultural practices. Stems were cut at the commercially acceptable maturity for experiments from May-July.

In most cases, growth regulator treatments were done immediately after harvest. Compounds used included: ProGibb (GA3), Provide (GA4+7), BAP-10 (benzyladenine, BA) and Fascination (contains an equal, 1:1 ratio of GA4+7 and BA).

Several experiments were conducted to investigate factors such as compound, concentration, method and duration of application (pulse, foliar spray or inclusion in vase solution).

After the treatments, stems were either transferred directly to a postharvest evaluation room (68° F with typical “indoor” fluorescent light at 12 hrs per day) or stored (dark, on water) at 36-37° F for up to two weeks prior to the transfer to the postharvest evaluation room. The standard vase solution in the postharvest room contained 3 percent sucrose and 200 ppm 8-hydroxyquinoline citrate.

Data on leaf quality (percentage yellow or necrotic leaves) and inflorescence longevity (time of wilting of the last open flower of the inflorescence) were recorded at regular intervals in the postharvest room, up to three weeks. Á

Results

Cultivar differences. Cut lily stems of most of the evaluated cultivars started showing symptoms of leaf yellowing approximately one week after placement in the postharvest room (well before the end of inflorescence life). This leaf yellowing was accelerated when stems were stored at 36-37° F for up to two weeks after the cut. Oriental, Asiatic and LA-hybrid cultivars varied greatly in their potential for leaf yellowing during postharvest evaluation (See Table 1). Overall, oriental cultivars tended to show more yellowing after the 2-week evaluation. Even so, the Oriental ‘Tom Pouce’, Asiatic ‘Vivaldi’ and the LA ‘Cebeco Dazzle’ showed less than 20 percent yellowing, even if the cut stems had been stressed by holding dark for two weeks on water, at 36-37° F prior to evaluation.

Method of application. GA4+7 was effective whether applied as a stem uptake (pulse) treatment, as a leaf/stem spray after harvest or as a vase solution component (See Table 2). For example, after two weeks in the postharvest room, the three cultivars used had 16-41 percent dead or yellow leaves, whereas plants with any of the treatments had less than 5 percent yellow leaves. Another general effect of gibberellin on lilies is an increase in flower longevity. For example, with ‘Star Gazer’, one can see flower life increasing from 12 to 14 days with gibberellin treatment. Á

Active compound. GA4+7 can also be seen to be the active component of the treatment, as GA4+7 applied individually was at least as effective as the combination of GA4+7 and BA (See Table 3). This is the same finding as we have seen in Easter lily and in potted Oriental hybrid lilies. Table 4 gives a further comparison of GA4+7 and GA3 in the LA-hybrid cultivar ‘Cebeco Dazzle’. While both GA’s are effective in increasing flower life, only the GA4+7 is active in preventing leaf yellowing.

Pulse duration and temperature. There appears to be wide latitude regarding concentrations, temperature and duration for GA4+7 pulses. Table 5 shows that a 6-hour pulse at 37° F was as effective as an 18-hour pulse at 68° F. In this preliminary experiment, we did not measure solution uptake but assume that much more uptake occurred with the longer and warmer treatment.

GA4+7 concentration. In another experiment with the Asiatic cultivar ‘Orandiso’, GA4+7 pulses at 25 ppm were equally effective as pulses at 100 ppm. There are, however, upper limits to GA4+7 use. In this experiment, the Asiatic cultivar ‘Marseille’ was subjected to water or long pulses of GA3 or GA4+7 at 100 or 500 ppm. The higher concentration of GA4+7 was phytotoxic to the plants and caused complete death. While this appears to be an extreme example, additional experiments need to be conducted to further define these parameters as they relate to commercial situations.

Gibberellins also prevented leaf yellowing in cut lily stems when included as a component in the vase solution. Effective concentrations of GA4+7 were 5-25 ppm. These treatments were also effective in the case of cold-stored stems.