Effect of 1-MCP on Cotton Plants under Abiotic Stress Caused by Ethephon
American Journal of Plant Sciences
Many environmental stress factors have been identified to increase square and boll abscission and thus result in reduced cotton yield. Under stress conditions, ethylene is elicited. Ethylene peaks before abscission to promote the formation of the abscission layer and plays a major role in early season square and boll abortion in cotton (Gossypium hirsutum L.). In addition, ethylene stimulates the leaf senescence process. Thus, it is desirable to protect plants from ethylene-induced fruit loss
... nduced fruit loss and premature leaf senescence under stress conditions. The objective of this study was to evaluate the ability of 1-methylcyclopropene (1-MCP) to protect cotton plants against abiotic stress caused by ethephon (ethylene promoting effect). Field studies using a randomized complete block design with four replications were conducted in 2010 and 2011 at Texas A&M AgriLIFE Research Farm in Burleson County, TX. Eight treatments that consisted of two 1-MCP rates (0 and 10 g a.i. ha −1 ) in combination with four ethephon rates (0, 146, 292, 438 mL•ha −1 ) were imposed at the first flower (FF) stage of the development. 1-MCP increased plant height and number of main stem nodes in both years. In addition, 1-MCP-treated plants exhibited greater membrane integrity and increased photosystem II quantum efficiency and thus delayed senescence in both years. These potentials for yield increase were realized in 2011 with 1-MCP treatment exhibiting a higher lint yield. In 2012, although 1-MCP treatment increased number of open fruit and open fruit weight per plant significantly, no significant lint yield increase was detected.  . Because boll retention is a major concern for cotton yield improvement, the role of ethylene in cotton fruit shedding has been studied extensively. Ethylene promotes the abscission layer formation in the peduncle in cotton plants, thus leading to fruit abortion  . In cotton, research has demonstrated that ethylene production plays a major role in early season square and boll abortion -  . Moreover, stress-induced ethylene synthesis can be elicited by temperature that is either high-temperature, freezing, or chilling, water stress including drought and waterlogging, chemicals including herbicides and insects salivary fluids, physical wounding including bruising, cutting and insect biting, and pathogens   . Additionally, stresses may further decrease boll retention as confirmed by the fact that ethylene production accelerates induction of fruit shed of cotton plants under drought    . Due to the crucial role that ethylene plays in square and boll loss, it is advantageous to protect plants from ethylene-induced fruit loss. Ethylene plays a primary role in the abscission of leaves - and fruit Ethylene is also a mediator in the senescence process in which cells undergo programmed cell death induced by developmental and environmental signals -  . When ethylene function was blocked, lower electrolyte leakage, indicating delayed senescence, was detected in flower petals - and leaves  . Enhanced chlorophyll degradation associated with ethylene production has been reported in many studies -. Leaf senescence often occurs during the boll filling stage in cotton  . At this critical stage, leaf senescence induced by ethylene caused a lower photosynthetic rate and less carbon accumulation and thereby decreased yield. Thus, as mentioned earlier, it is desirable to protect yield by reducing the ethylene effect which can reduce fruit shedding and lead to a delay of senescence. The plant growth regulator 1-methylcyclopropene (1-MCP), which inhibits ethylene action, has been proven to be a valuable product in industry to improve quality and shelf life of horticultural products  . 1-MCP is a gas at room temperature with a formula of C 4 H 6 . 1-MCP occupies the ethylene receptor site and has an affinity 10 times greater for the site than that of ethylene  . Thus, 1-MCP may inhibit ethylene action by competing with ethylene for the ethylene receptor to inhibit binding. Ethephon (2-chloroethylphosphonic acid; Ethrel) is an ethylene-releasing compound that is metabolized to ethylene in plants. Ethephon is a widely used plant growth regulator since the 1960s. This compound is used to facilitate fruit ripening, senescence, abscission, flower induction in pineapple, and to also retard stem growth on cereal crops to reduce lodging. The primary use of this chemical is in cotton harvesting. Ethylene accelerates opening of cotton bolls and improves cotton responses to defoliants; thus ethephon usually makes up a part of defoliation programs   . da Costa et al. (2011)  tested the effect of ethephon on 1-MCP treated cotton plants. Because we found that 1-MCP works more efficiently in stress conditions (water stress, heat stress, and ageing) (unpublished data), our present study was designed to test effect of 1-MCP under different stress levels applied as different rates of ethephon in the field conditions by assessing leaf senescence traits and yield related data.