Using Gibberellins to Prevent Leaf Yellowing in Cut Lilies
Hybrid lilies are excellent cut flowers due to theavailability of flowers with various colors and shapes. Extensive inter-specieshybridization has resulted in numerous cultivars, and many new cultivars areintroduced to the market each year. While the vigor and reliability of the crophas improved over the years, what has not changed is that successful usedepends on the postharvest quality of the cut stem.
The postharvest performance of cut lilies is dependent onmany factors, such as the cultivar, preharvest conditions, stage of harvest,and postharvest environment and handling. Vase life of the cut stem usuallyends when flower petals wilt or turn brown, but leaf quality is anotherimportant 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 beencold-stored for any length of time prior to marketing. Generally, the vase lifeof cut lilies varies from 5-14 days, depending on the cultivar.
The potential use of growth regulators, especiallygibberellins and cytokinins, has not been studied adequately in cut lilies. Ourprevious studies have shown that spray treatments with GA4+7 alone or incombination with BA (i.e., Fascination, Valent USA) remarkably reducecold-induced leaf yellowing in pot hybrid lilies and gradual leaf yellowing inEaster lilies. We have also seen positive effects on flower longevity in thesehormone-treated plants. These observations warranted the investigation ofpotential use of these chemicals in cut lilies.
This research was carried out to investigate the potentialuse of gibberellins and benzyladenine (BA) to improve postharvest quality ofcut hybrid lilies. Experiments were conducted using various cultivars fromdifferent groups of hybrid lilies to test different aspects of treatment, suchas the concentration, method of application and time of application. We want toemphasize that this is a research report and that the chemicals evaluated inthis project are not currently labeled for use on cut lilies. Please contactyour chemical representative before any new usage and always follow chemicallabels.
Experiments were conducted with a range of commerciallyimportant cultivars of Oriental, Asiatic and LA-hybrid lilies. Cultivars testedinclude Asiatics ‘Amarone’, ‘Colosseo’,‘Marseille’, ‘Orandiso’, ‘Vermeer’ and ‘Vivaldi’;Orientals ‘Berlin’, ‘Helvetia’, ‘Muscadet’,‘Tom Pouce’, ‘Star Gazer’ and ‘Sissi’; andLA-hybrids ‘Cebeco Dazzle’, ‘Fangio’, ‘RoyalParade’, ‘Royal Perfume’ and ‘Samor’. Plants weregrown in Á bulb crates with MetroMix 360 in Cornell University greenhousesaccording to standard cultural practices. Stems were cut at the commerciallyacceptable maturity for experiments from May-July.
In most cases, growth regulator treatments were doneimmediately after harvest. Compounds used included: ProGibb (GA3), Provide(GA4+7), BAP-10 (benzyladenine, BA) and Fascination (contains an equal, 1:1ratio of GA4+7 and BA).
Several experiments were conducted to investigate factorssuch as compound, concentration, method and duration of application (pulse,foliar spray or inclusion in vase solution).
After the treatments, stems were either transferred directlyto a postharvest evaluation room (68° F with typical “indoor”fluorescent light at 12 hrs per day) or stored (dark, on water) at 36-37° Ffor up to two weeks prior to the transfer to the postharvest evaluation room.The standard vase solution in the postharvest room contained 3 percent sucroseand 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 theinflorescence) were recorded at regular intervals in the postharvest room, upto three weeks. Á
Cultivar differences.Cut lily stems of most of the evaluated cultivars started showing symptoms ofleaf yellowing approximately one week after placement in the postharvest room(well before the end of inflorescence life). This leaf yellowing wasaccelerated when stems were stored at 36-37° F for up to two weeks afterthe cut. Oriental, Asiatic and LA-hybrid cultivars varied greatly in theirpotential for leaf yellowing during postharvest evaluation (See Table 1).Overall, oriental cultivars tended to show more yellowing after the 2-weekevaluation. Even so, the Oriental ‘Tom Pouce’, Asiatic‘Vivaldi’ and the LA ‘Cebeco Dazzle’ showed less than20 percent yellowing, even if the cut stems had been stressed by holding darkfor 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 aleaf/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 usedhad 16-41 percent dead or yellow leaves, whereas plants with any of the treatmentshad less than 5 percent yellow leaves. Another general effect of gibberellin onlilies is an increase in flower longevity. For example, with ‘StarGazer’, one can see flower life increasing from 12 to 14 days withgibberellin treatment. Á
Active compound.GA4+7 can also be seen to be the active component of the treatment, as GA4+7applied individually was at least as effective as the combination of GA4+7 andBA (See Table 3). This is the same finding as we have seen in Easter lily andin potted Oriental hybrid lilies. Table 4 gives a further comparison of GA4+7and GA3 in the LA-hybrid cultivar ‘Cebeco Dazzle’. While bothGA’s are effective in increasing flower life, only the GA4+7 is active inpreventing leaf yellowing.
Pulse duration and temperature. There appears to be wide latitude regardingconcentrations, temperature and duration for GA4+7 pulses. Table 5 shows that a6-hour pulse at 37° F was as effective as an 18-hour pulse at 68° F. Inthis preliminary experiment, we did not measure solution uptake but assume thatmuch more uptake occurred with the longer and warmer treatment.
GA4+7 concentration.In another experiment with the Asiatic cultivar ‘Orandiso’, GA4+7pulses 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+7at 100 or 500 ppm. The higher concentration of GA4+7 was phytotoxic to theplants and caused complete death. While this appears to be an extreme example,additional experiments need to be conducted to further define these parametersas they relate to commercial situations.
Gibberellins also prevented leaf yellowing in cut lily stemswhen included as a component in the vase solution. Effective concentrations ofGA4+7 were 5-25 ppm. These treatments were also effective in the case ofcold-stored stems.