The severity of ethylene damage depends on the sensitivity of the plant species to ethylene, the concentration of ethylene, the amount of time the plant is exposed, and the temperature. High temperature stress causes plants to produce more ethylene, but plants are also more sensitive to damage from ethylene contamination at higher temperatures. In general, young flower buds are less sensitive to ethylene damage than open flowers, and leaves are less sensitive than flowers. Figure 1 shows how the dose of ethylene (concentration over time) affects impatiens.
In a greenhouse production environment plants may be exposed to lower concentrations (25 to 200 ppb; parts per billion) of ethylene over weeks or even months during the colder times of the year. This type of chronic ethylene exposure results in stunted or malformed growth, flowers that do not initiate, and flower bud abortion. If grown to flowering under these conditions, the flowers become smaller and show accelerated death. Leaves start to prematurely yellow (i.e. chlorosis) and eventually they will become brown and dry (i.e. necrotic). This type of ethylene damage can be hard to diagnosis, because similar symptoms may result from nutrient or pathogen disorders. In many instances where constant low levels of ethylene are present in the production environment, you may first observe damage on ethylene sensitive crops grown in hanging baskets (like geraniums). This is because ethylene is lighter than air and it will accumulate to higher concentrations up in the peak of the greenhouse.
If exposed to higher levels of ethylene, in the ppm (parts per million) range, ethylene damage occurs much more quickly. At 1 ppm, ethylene is considered to have full biological activity and most plants will show some signs of damage within hours or a few days. This damage is much easier to attribute to ethylene. In these instances it is likely that plants will be growing well and you will come in one morning to find that all the open flowers on your geranium baskets have been shed. Symptoms of acute ethylene damage include shedding or shattering of leaves, buds or petals, rapid flower aging (i.e. senescence) and wilting or leaf yellowing (Figure 2). A classic symptom of ethylene damage is epinasty (Figure 3). This is the characteristic downward growth of the leaf petiole. Plants look like they are experiencing drought stress, but they are well hydrated and fully turgid. While many different plants show epinasty, tomatoes consistently show the most severe epinasty at the lowest concentrations of ethylene.
Will ethylene damaged plants recover?
This is a hard question to answer. In most instances ethylene damage will not kill your crop, but it will often impact the marketability of the crop by delaying flowering or by removing all open flowers. Ethylene damage at the young seedling stage can result in plant death and entire crops may need to be replanted. The geranium hanging basket shown in Figure 3 was produced in a greenhouse that contained 800 ppb ethylene over a period of multiple weeks (or longer). Extensive damage like this essentially results in a crop that is not saleable. When removed from the ethylene environment, new growth resumed on these baskets but flowering was delayed by over one month (Figure 3). Most plants with moderate damage will resume normal vegetative growth and flowering within 1 to 2 weeks. In contrast, plants like tulips and Easter lilies, that flower only once, will not recover when buds and open flowers have been damaged by ethylene. Plants experiencing epinasty will recover quite quickly and these crops are the most likely to remain of marketable quality.
Dr. Michelle L. Jones
D.C. Kiplinger Chair in Floriculture
The Ohio State University
Department of Horticulture and Crop Science