Physiological effects on plant growth caused by the plant hormone ethylene have been noted for many years. More than 100 years ago, workers noted that illuminating gas or broken gas mains had deleterious effects on surrounding trees or plants. It was not until the 1960s that scientists documented that plant growth may be manipulated by applying ethylene. Some of the biological effects since noted include premature defoliation, fruit maturation ripening, induction of flowering, stimulation of sprouting or germination, and shortening of plant height. These effects are noted on a wide variety of agricultural crops, including vegetables, field crops, tree crops, and ornamentals. Ethylene is a gas and dissipates rapidly, and, thus, does not lend itself to field application. In the 1960s, the product ethephon [(2-chloroethyl)phosphonic acid] was developed. When taken up by the plant, ethephon is converted to ethylene in the cells and becomes available for physiological interactions. Because ethephon precipitates a wide variety of biological reactions, application technology becomes extremely important. Factors such as plant growth stage, plant stress status, plant foliage spray coverage, ethephon rates, and environmental conditions determine the responses obtained. An example is provided by processing tomatoes, where the desired response is to maximize fruit maturity enhancement and minimize premature defoliation—both ethylene responses. We have selected five agricultural applications of ethephon as examples of how plant growth may be altered. These are: increased boll opening in cotton; enhanced pistillate flower induction in hybrid squash seed; accelerated fruit maturity in processing tomatoes; enhanced hull splitting in walnuts; and reduced lodging in wheat. Each of these applications, and others, are common in California agriculture. Brevity necessitates providing only a summary of relevant applied research activities, which are not intended to be complete or thorough. Details on specific ethephon applications may be obtained from that particular researcher.
Mike Murray, Bob Beede, Bill Weir and Jack Williams
Mike Murray, Mike Cahn, Janet Caprile, Don May, Gene Miyao, Bob Mullen, Jesus Valencia and Bill Weir
University of California Cooperative Extension farm advisors have conducted applied research to quantify processing tomato [Lycopersicum esculentum (L.) Mill] varietal performance, as a coordinated activity, since 1973. Early and midseason maturity varieties are annually evaluated at four to six locations throughout the state. The test varieties are selected in collaboration with seed companies, processors and growers. The growers and seed companies provide financial support for the tests. Most tests are conducted in production tomato fields and are harvested using commercial harvesters. The results are widely disseminated through an annual report to the funding sources, farm advisor research reports, newsletters, production meetings, the California Tomato Grower magazine, and popular media. The information obtained for fruit yield potential, fruit quality and plant horticultural characteristics is used by processors, growers, and seed companies to make variety selection decisions. This regional extension program has proven to be an effective way to generate well-designed replicated information for making intelligent processing tomato cultivar decisions and has been well accepted by the California industry.