Foliar chlorosis of Kalanchoe blossfeldiana Poelln. as influenced by temperature, darkness, and ethylene.

Kalanchoe blossfeldiana Poelln. plants were held in simulated shipping environments with variables of air ± 0.5 ppm ethylene, temperature, and light exposure regimes for 2 and 3 days. Plants held in light (1.3 klx for 12 hr/day) for 2 days at 23.5°C did not become chlorotic, whereas those held in darkness became severely chlorotic. Ethylene increased the number of chlorotic leaves on plants held in the dark but had no effect when plants were held in the light. With each successive increase in temperature from 23 to 28 to 33°C, plants held in darkness with or with out ethylene had increased leaf chlorosis. Plants held in darkness for 3 days contained less chlorophyll than those held for 2 days. These simulated shipping tests suggested that, in transit, leaf chlorosis of kalanchoe occurs when plants are packaged (held in darkness) and subjected to elevated temperatures for 2 or more days. Kalanchoe plants have increased in popularity in the last few years, and the increased demand for this flowering plant has resulted in an increase in the numbers of propagat ing specialists who produce the plants asexually (from cuttings) and ship them to growers, who force the plants to flowering size. Plants generally have been observed to arrive at their destination in poor condition, principally because of leaf chlorosis. Although some reports are avail able on the effects of environment during the growing iFlorida Agricultural Experiment Stations Journal Series No. 2690. 2Research accomplished at U. S. Dept. Agr. , SEA, AR, and Univ. of FL, AREC, Bradenton, FL. Proc. Fla. State Hort. Soc. 93: 1980. period (8, 9, 10), little research has been reported on the shipping and handling environment of kalanchoe. Marousky and Harbaugh (5) reported that minute quanti ties of ethylene induced floret sleepiness, foliar chlorosis, and abscission in mature flowering plants. Sheehan and Nell (11) reported that light and fertilizer used during the plant growing phase influenced the degree of chlorosis during the postharvest phase. In this paper, we report the effects of temperature, darkness, and ethylene on development of leaf chlorosis and loss of chlorophyll in Kalanchoe blossfeldiana Poelln. plants during simulated shipping conditions. Materials and Methods Kalanchoe plants in 6 cm (2.3 inch) square plastic pots were obtained commercially. Plants were 2-3 weeks old (after transplanting) and had been growing under a short night environment (i.e. vegetative). All experiments were started and terminated during the afternoon and repeated at least once. All treatments had a minimum of 6 plants. The general procedures for mixing ethylene and air and dis tributing gases in chambers were similar to those previously reported (6). Air and ethylene flow was regulated to pro vide one complete change of air per chamber every 30-35 min. After exposure, the number of chlorotic leaves on each plant was counted. In some experiments, chlorophyll levels were determined. One gram of tissue was collected from the lower leaf blades, and chlorophyll was extracted with 80% acetone and determined according to the technique of Arnon (2). Chlorophyll was expressed as milligrams per 100 grams of leaf tissue. Experiment 1. 'Goddess' and 'Conquistador* kalanchoe plants were placed in chambers in a laboratory maintained at 23.5 ± 1°C. Plants were held in light (1.3 klx/12 hr/day) or in darkness in air ± 0.5 ppm ethylene for 2 days. Experiment 2. 'Goddess' and 'Conquistador' plants were placed in chambers held in darkness in incubators main tained at 23, 28, and 33 dz 0.5°C. Each chamber contained air dz 0.5 ppm ethylene. The numbers of chlorotic leaves and chlorophyll content in plants were determined after a 3-day exposure. Experiment 3. 'Tabasco' plants were held for 2 and 3