Crj70189 1666..1672

Whole plant defoliation studies were performed using dark red kidney bean (Phaseolus vulgarisL.) to compare the effect of cyclanilide [1(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid], ethephon (2-chloroethylphosphonic acid), auxin transport inhibitors, and temperature on leaf abscission. Ethephon induced bean leaf defoliation, but ethephon combinedwith cyclanilide induced greater defoliation than ethephon alone. The response was dose dependent, as 0.067 kg/ha ethephon alone did not induce defoliation, but when combined with an equal rate of cyclanilide induced 63% defoliation five days after treatment (DAT). In addition, combining auxin transport inhibitors at 0.140 kg a.i./ha with 0.067 kg a.i./ha ethephon induced 50 to 52% defoliation, 5 DAT. Ethephon-induced defoliation was more temperature sensitive than the combination of cyclanilide with ethephon. Ethephon alone (0.067 kg a.i./ha) induced 26% defoliation 5 DAT at the highest tested temperature (30/26 C, day/night), but cyclanilide combined with ethephon induced 75 to 85% defoliation at all tested temperatures (except at 16/14 C, the lowest). These results indicate that cyclanilide is an ethephon synergist because it enhanced ethephon activity, even at low temperatures. These results support the model that ethylene released by ethephon induces abscission, and suggests that inhibition of auxin transport or auxin signaling will increase the effect of ethylene on the process of leaf abscission. Because of the similarities to the activity to 1-N-naphthylphthalamic acid (NPA) and 2,3,4-triiodobenzoic acid (TIBA) in vivo, cyclanilide may act as an auxin transport inhibitor. DEFOLIANTS AND DESICCANTS are classified as harvest aid chemicals because they are commonly used to facilitate mechanical harvesting of crops. In cotton (Gossypium hirsutum L.), defoliation prior to harvest is important because the pigments in the leaves can stain and reduce the quality of the cotton fiber (Nickell, 1982, p. 19–27). In addition, removal of foliage prior to harvest will result in cotton that has less debris. Defoliants or desiccants are also used to synchronize and enhance boll opening in cotton, thus allowing the farmer to obtain maximum yield in a single harvest. In addition to cotton, soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.), potato (Solanum tuberosumL.), grain sorghum [Sorghum bicolor (L.) Moench], sunflower (Helianthus annuus L.), lentil (Lens culinaris Medik.), trefoil (Lotus spp.), dry bean (Phaseolus vulgaris L.), and sugarcane (Saccharum spp.) are often desiccated to facilitate harvest (Yang, 1986). In fruit crops such as olive (Olea europaea L.), apple (Malus spp.), pear (Pyrus spp.), peach [Prunus persica (L.) Batsch], and citrus (Citrus spp.), chemicals that act as defoliants are used to facilitate the loosening of fruit from trees prior to mechanical harvesting or to synchronized fruit ripening (Cooper et al., 1968; Edgerton and Blanpied, 1968). Defoliants and desiccants are therefore used to increase crop yield, improve crop quality, and improve harvest efficiency. FINISH is a harvest aid chemical produced by Bayer Crop Science, Monheim, Germany, labeled for use in cotton. It is used to enhance defoliation, accelerate boll opening, and prevent terminal regrowth (FINISH label, Bayer Crop Science). FINISH contains two active ingredients: ethephon and cyclanilide. Ethephon was initially registered for use in 1971, but was not used in cotton until the mid 1980s. In the mid 1990s, FINISH was introduced, because ethephon efficacy in cotton was enhanced when combined with the compound cyclanilide (Stewart et al., 2000). The use of FINISH compares favorably with other cotton harvest aid treatments when evaluated on yield and harvest quality (Larson et al., 2002). Cyclanilide has also been used alone to induce lateral branching in apple trees (Elfving and Visser, 2005). Cyclanilide is a malonanilate, and has a cyclopropane ring similar to 1-aminocyclopropane-1-carboxylic acid (Fig. 1). Defoliation or leaf abscission is induced in plants as a natural process in response to environmental changes, pest or pathogen attack, or can be induced with the application of synthetic chemicals (Osborne, 1989; Roberts et al., 2002). The plant hormones auxin and ethylene are the main plant growth regulators which control natural leaf abscission. While auxin suppresses abscission, ethylene promotes abscission (Addicott, 1982; Taylor and Whitelaw, 2001). Applying auxin at a distal position in reference to the abscission zone can inhibit leaf abscission even after the abscission process has begun (Chatterjee and Leopold, 1963). Combinations of auxin and ethylene induced the transdifferentiation of cortical cells to abscission cells (McManus et al., 1998). Synthetic auxins such as 1-Naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid have commonly been used in fruits to prevent yield loss by inhibiting early fruit drop or abscission (Cooper et al., 1968). Ethylene is the main hormone that promotes abscission by inducing the production of various cell wall hydrolases in the abscission zone to stimulate cell wall breakdown and eventual shedding (Campillo and Lewis, 1992; Sexton and Roberts, 1982). The hormone balance model for leaf abscission proposes that there are two general temporal phases in an expanding leaf (Rubinstein and Leopold, 1963; Osborne, 1989; Taylor and M.K. Pedersen and J.D. Burton, North Carolina State University, Dep. of Horticulture Science, Box 7609, Raleigh, NC 27695; H.D. Coble, USDA/ARS/OPMP, Washington, DC 20250. Received 6 July 2005. *Corresponding author ([email protected]). Published in Crop Sci. 46:1666–1672 (2006). Forage & Grazinglands doi:10.2135/cropsci2005.07-0189 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: DAT, days after treatment; IAA, indole-3-acetic acid; MDR, multidrug resistance; NPA, 1-N-naphthylphthalamic acid; TIBA, 2,3,4-triiodobenzoic acid. R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 1666 Published online June 20, 2006