1-Methylcyclopropene (1-MCP) Chris B. Watkins Department of Horticulture, Cornell University, Ithaca, NY The plant hormone ethylene affects a wide range of physiological processes in horticultural crops, including abscission, senescence and ripening, chlorophyll loss, softening, physiological disorders, sprouting, isocoumarin synthesis, lignification, discoloration (browning), decay, and stimulation of defense systems (Saltveit 1999). Depending on the desired use of the produce, these effects can be positive or negative. However, most postharvest handling is focused on controlling ethylene production or action. Among the available methods, chemical control of ethylene biosynthesis by aminoethoxyvinylglycine (AVG) and inhibition of its action by 1-methylcyclopropene (1-MCP) have become useful tools for the horticulture industry as they seek to maintain quality of produce after harvest (Venburg et al. 2008, Watkins 2008c). 1-MCP belongs to a class of compounds known as cyclopropenes. The discovery that cyclopropenes inhibit ethylene perception by competitively binding to ethylene receptors represented a major breakthrough in controlling ethylene responses of horticultural products (Blankenship and Dole 2003). The process of discovery of the effects of cyclopropenes and their proposed method of action has been described (Sisler and Serek 2003, Sisler 2006). 1-MCP has several characteristics that make it conveniently useful by the fresh produce industry. It is a gaseous molecule that is easily applied, has an excellent safety profile, leaves no residues in or on treated produce, and is active at very low concentrations (parts per billion). Of the cyclopropenes, 1-MCP proved to be extremely active, but it is unstable in the liquid phase. A process has been developed in which 1-MCP is complexed with α-cyclodextrin, maintaining the stability of 1-MCP. After application, 1-MCP is released from the complex to expose horticultural products to the molecule. When applied during the preharvest period, 1-MCP has the useful effects of delaying fruit drop, slowing fruit maturation and ripening, and maintaining postharvest quality (McArtney et al. 2008, Watkins 2010, Watkins et al. 2010). Produce must be exposed to 1-MCP at an effective rate and for a sufficiently long time to elicit physiological responses. In essence, this means applying a higher preharvest concentration of 1-MCP than that used for postharvest application, while ensuring stability of the formulation without inducing phytotoxicity. Some reports on postharvest dipping of fruit into aqueous 1-MCP have been published (Choi et al. 2008), but this method is not currently used commercially. Registration

The U.S. Environmental Protection Agency (EPA) approved use of 1-MCP on floriculture and ornamental products in 1999 and on edible food products in 2002. By 2011, more than 40 countries had approved use of 1-MCP. It is registered for use on a wide variety of fruits and vegetables including apple, apricot, Asian pear, avocado, banana, broccoli, calabrese, cauliflower, Brussels sprouts, cabbage, carrot, cherimoya, cucumber, date, guava, kiwifruit, lime, mango, melon, nectarine, papaya, paprika, peach, pear, pepper, persimmon, pineapple, plantain, plum, plumcot, squash, tomato, and many ornamentals. The specific products for which 1-MCP is registered in each country vary greatly according to the importance of the crop in that country. For example, 1-MCP can be applied to tulip bulbs in the Netherlands. Recently, 1-MCP formulations have been approved by the EPA and other regulatory authorities for preharvest application. Semicommercial trials have been carried out at several locations in the United States, Argentina, Brazil, Canada, Chile, New Zealand, and South Africa. Effects of 1-MCP on Fruits, Vegetables, and Ornamental Products The availability of 1-MCP has provided outstanding opportunities for researchers to investigate both ethylene-dependent and ethylene-independent events during ripening and senescence, in addition to developing practical uses for 1-MCP. Studies have focused on the effects of 1-MCP on quality of horticultural crops, specific postharvest issues such as handling and packaging, physiological and biochemical responses, and storage disorders. A number of detailed reviews on the effects of 1-MCP have been published (Blankenship and Dole 2003, Serek et al. 2006, Watkins 2006,2007, Huber 2008, Watkins 2008a,2008b,2010). These reviews report on the use of an extensive range in 1-MCP concentration, depending on the responsiveness of the product to the molecule. Ripening and Senescence. 1-MCP affects many ripening and senescence processes, including pigments, softening and cell wall metabolism, flavor and aroma, and nutritional properties (Watkins 2006,2008b, Serek et al. 2006). These processes are affected to varying degrees in both nonclimacteric and climacteric products. The range of responses reflects the enormous diversity of these crops in terms of both inherent diversity and morphological derivation (Huber 2008). Several generalizations can be made about responses of crops to 1-MCP:

• Genotype, cultivar, and maturity effects can be highly variable, but responses to 1-MCP are typically “concentration × exposure time” dependent.

• Most if not all climacteric fruit are affected by 1-MCP treatment, but the capacity to interrupt the progression of ripening, once initiated, varies by fruit and by attributes studied.

• Nonclimacteric fruit can also respond to 1-MCP; such effects are providing interesting insights about ethylene-dependent and ethylene-

independent events during ripening. • Treated fruit are firmer, slower to soften, slower to change peel color and

they develop aroma and flavor slower, but if 1-MCP concentrations and exposure periods are appropriate for the product, the final quality attained in the ripened fruit is similar to that of untreated product.

• Rate of loss of nutritionally important compounds such as vitamin C are usually reduced in 1-MCP-treated fruits and vegetables, and effects on phenolic compounds are minor.

Physiological Disorders. An important area of postharvest responses to 1-MCP is its effects on physiological disorders (Watkins 2007,2008a,2008b). These disorders can be divided into categories:

• Ethylene-induced disorders. Examples include russet spotting of lettuce and isocoumarin accumulation in carrots (Fan and Mattheis 2000a), lignification of asparagus (Liu and Jiang 2006), and water-soaking of watermelons (Mao et al. 2004). These disorders are preventable by inhibition of ethylene production.

• Senescence-related disorders. Examples include senescent breakdown of apples (Moran and McManus 2005), senescent scald and breakdown of pears (Ekman et al. 2004), and yellowing of broccoli (Fan and Mattheis 2000b). These disorders are also prevented by inhibition of ethylene production.

• Controlled atmosphere-related storage disorders. 1-MCP can increase susceptibility of apple fruit to carbon dioxide injuries. Incidence of both internal and external forms of injury is increased by 1-MCP (DeEll et al. 2003, Fawbush et al. 2008, Argenta et al. 2010).

• Chilling-related disorders that are increased by inhibition of ethylene production. Examples include woolliness and internal breakdown of peaches and nectarines (Dong et al. 2001), chilling injury of citrus and bananas (Porat et al. 1999, Jiang et al. 2004), and flesh browning of the ‘Empire’ apple (Watkins 2008b).

• Chilling-related disorders that are decreased by inhibition of ethylene production. Examples include superficial scald; brown core (coreflush) and soft scald of apples and pears (Fan et al. 1999); internal flesh browning of avocados and pineapples (Selvarajah et al. 2001, Pesis et al. 2002); and chilling injury of bamboo shoots (Luo et al. 2008), melons (Gal et al. 2006), and persimmon (Luo 2007).

Pathological Disorders: Disease incidence can be increased, decreased, or unaffected by 1-MCP, depending on the product, although results are not always consistent because of the complex interaction between host, pathogen, and environment (Watkins 2008b). In some instances, disease incidence can be lower because the beneficial effects of 1-MCP on skin integrity and flesh firmness result in greater resistance to infection. However, ethylene is necessary for defense systems in other plant systems (Marcos et al. 2005).

Application For postharvest use of 1-MCP on both ornamental plants and edible food products, material must be treated in an enclosed area, such as a storage room, greenhouse, trailer, or shipping container. Leakage of 1-MCP from the treatment area can reduce its concentration and therefore effectiveness. 1-MCP can only be applied by authorized service providers, not by commercial storage operators. Testing of rooms for leakage, certification of product quality, and application of the proper 1-MCP concentration for the product maximize the benefits of treatment. The apple has been an excellent crop for use of 1-MCP, which is used extensively around the world to maintain quality through the whole marketing chain from storage to consumer (Watkins 2008b). Applications rates for apples vary from 625 to 1,000 nL L-1, depending on the country of registration. The major benefit of 1-MCP to the grower is more time to get high quality produce through marketing channels to the consumer. The successful use of 1-MCP on apples is largely associated with varieties for which maintenance of at-harvest quality and only moderate softening to a crisp texture is desirable. In contrast, challenges exist for effective use of 1-MCP on fruits that ripen to a melting texture or have major color change. For example, failure to ripen normally has been shown in avocado, banana, pear, and tomato after fruit were treated at an early ripening stage or if the applied 1-MCP concentration was too high (Golding et al. 1998, Mir et al. 2004, Hurr et al. 2005, Bai et al. 2006). Fruit must ripen uniformly to quality characteristics (texture, flavor, aroma, color) that are expected by the consumer. Despite the challenges, successful 1-MCP treatment of avocados, bananas, melons, persimmons, and tomatoes has resulted from careful attenuation of 1-MCP concentrations or selecting fruit at the appropriate ripening stage at harvest. Research on reinitiating ripening after 1-MCP treatment in extremely sensitive fruit like pear is ongoing (Bai et al. 2006, Chiriboga et al. 2011, Villalobos-Acuna et al. 2011). A considerable amount of research on crops other than apple is proprietary and therefore not yet in the public domain. References Argenta, L.C., J.P. Mattheis, and X.T. Fan. 2010. Interactive effects of CA storage, 1-methylcyclopropene and methyl jasmonate on quality of apple fruit. Acta Hort. 857:259-266. Bai, J., J.P. Mattheis, and N. Reed. 2006. Re-initiating softening ability of 1-methylcyclopropene-treated ‘Bartlett’ and ‘d’Anjou’ pears after regular air or controlled atmosphere storage. J. Hort. Sci. Biotechnol. 81:959-964. Blankenship, S.M., and J.M. Dole. 2003. 1-Methylcyclopropene: a review. Postharv. Biol. Technol. 28:1-25.

Chiriboga, M.A., W.C. Schotsmans, C. Larrigaudiere, et al. 2011. How to prevent ripening blockage in 1-MCP-treated ‘Conference’ pears. J. Sci. Food Agric. 91:1781-1788. Choi, S.T., P. Tsouvaltzis, C.I. Lim, and D.J. Huber. 2008. Suppression of ripening and induction of asynchronous ripening in tomato and avocado fruits subjected to complete or partial exposure to aqueous solutions of 1-methylcyclopropene. Postharv. Biol. Technol. 48:206-214. DeEll, J.R., D.P. Murr, L. Wiley, and M.D. Porteous. 2003. 1-Methylcyclopropene (1-MCP) increases CO2 injury in apples. Acta Hort. 600:277-280. Dong, L., H.W. Zhou, L. Sonego, et al. 2001. Ethylene involvement in the cold storage disorder of ‘Flavortop’ nectarine. Postharv. Biol. Technol. 23:105-115. Ekman, J.H., M. Clayton, W.V. Biasi, and E.J. Mitcham. 2004. Interactions between 1-MCP concentration, treatment interval and storage time for ‘Bartlett’ pears. Postharv. Biol. Technol. 31:127-136. Fan, X.T., and J.P. Mattheis. 2000a. Reduction of ethylene-induced physiological disorders of carrots and iceberg lettuce by 1-methylcyclopropene. HortScience 35:1312-1314. Fan, X.T., and J.P. Mattheis. 2000b. Yellowing of broccoli in storage is reduced by 1-methylcyclopropene. HortScience 35:885-887. Fan, X.T., J.P. Mattheis, and S. Blankenship. 1999. Development of apple superficial scald, soft scald, core flush, and greasiness is reduced by MCP. J. Agric. Food Chem. 47:3063-3068. Fawbush, F., J.F. Nock, and C.B. Watkins. 2008. External carbon dioxide injury and 1-methylcyclopropene (1-MCP) in the ‘Empire’ apple. Postharv. Biol. Technol. 48:92-98. Gal, S., S. Alkalai-Tuvia, Y. Elkind, and E. Fallik. 2006. Influence of different concentrations of 1-methylcyclopropene and times of exposure on the quality of ‘Galia’-type melon harvested at different stages of maturity. J. Hort. Sci. Biotechnol. 81:975-982. Golding, J.B., D. Shearer, S.G. Wyllie, and W.B. McGlasson. 1998. Application of 1-MCP and propylene to identify ethylene-dependent ripening processes in mature banana fruit. Postharv. Biol. Technol. 14:87-98. Huber, D.J. 2008. Suppression of ethylene responses through application of 1-

methylcyclopropene: a powerful tool for elucidating ripening and senescence mechanisms in climacteric and nonclimacteric fruits and vegetables. HortScience 43:106-111. Hurr, B.M., D.J. Huber, and J.H. Lee. 2005. Differential responses in color changes and softening of ‘Florida 47’ tomato fruit treated at green and advanced ripening stages with the ethylene antagonist 1-methylcyclopropene. HortTechnology 15:617-622. Jiang, Y.M., D.C. Joyce, W.B. Jiang, and W.J. Lu. 2004. Effects of chilling temperatures on ethylene binding by banana fruit. Plant Growth Regul. 43:109-115. Liu, Z.Y., and W.B. Jiang. 2006. Lignin deposition and effect of postharvest treatment on lignification of green asparagus (Asparagus officinalis L.). Plant Growth Regul. 48:187-193. Luo, Z.S. 2007. Effect of 1-methylcyclopropene on ripening of postharvest persimmon (Diospyros kaki L.) fruit. LWT—Food Sci. Technol. 40:285-291. Luo, Z.S., X.L. Xu, and B.F. Yan. 2008. Use of 1-methylcyclopropene for alleviating chilling injury and lignification of bamboo shoot (Phyllostachys praecox f. prevernalis) during cold storage. J. Sci. Food Agric. 88:151-157. Mao, L.C., Y. Karakurt, and D.J. Huber. 2004. Incidence of water-soaking and phospholipid catabolism in ripe watermelon (Citrullus lanatus) fruit: induction by ethylene and prophylactic effects of 1-methylcyclopropene. Postharv. Biol. Technol. 33:1-9. Marcos, J.F., L. Gonzalez-Candelas, and L. Zacarias. 2005. Involvement of ethylene biosynthesis and perception in the susceptibility of citrus fruits to Penicillium digitatum infection and the accumulation of defence-related mRNAs. J. Exp. Bot. 56:2183-2193. McArtney, S.J., J.D. Obermiller, J.R. Schupp, et al. 2008. Preharvest 1-methylcyclopropene delays fruit maturity and reduces softening and superficial scald of apples during long-term storage. HortScience 43:366-371. Mir, N., M. Canoles, R. Beaudry, et al. 2004. Inhibiting tomato ripening with 1-methylcyclopropene. J. Amer. Soc. Hort. Sci. 129:112-120. Moran, R.E., and P. McManus. 2005. Firmness retention, and prevention of coreline browning and senescence in ‘Macoun’ apples with 1-methylcyclopropene. HortScience 40:161-163. Pesis, E., M. Ackerman, R. Ben-Arie, et al. 2002. Ethylene involvement in

chilling injury symptoms of avocado during cold storage. Postharv. Biol. Technol. 24:171-181. Porat, R., B. Weiss, L. Cohen, et al. 1999. Effects of ethylene and 1-methylcyclopropene on the postharvest qualities of ‘Shamouti’ oranges. Postharv. Biol. Technol. 15:155-163. Saltveit, M.E. 1999. Effect of ethylene on quality of fresh fruits and vegetables. Postharv. Biol. Technol. 15:279-292. Selvarajah, S., A.D. Bauchot, and P. John. 2001. Internal browning in cold-stored pineapples is suppressed by a postharvest application of 1-methylcyclopropene. Postharv. Biol. Technol. 23:167-170. Serek, M., E.J. Woltering, E.C. Sisler, et al. 2006. Controlling ethylene responses in flowers at the receptor level. Biotechnol. Adv. 24:368-381. Sisler, E.C. 2006. The discovery and development of compounds counteracting ethylene at the receptor level. Biotechnol. Adv. 24:357-367. Sisler, E.C., and M. Serek. 2003. Compounds interacting with the ethylene receptor in plants. Plant Biol. 5:473-480. Venburg, G.D., R. Hopkins, J. Retamales, et al. 2008. Recent developments in AVG research. Acta Hort. 796:43-49. Villalobos-Acuna, M.G.V., W.V. Biasi, E..J. Mitcham, and D. Holcroft. 2011. Fruit temperature and ethylene modulate 1-MCP response in ‘Bartlett’ pears. Postharv. Biol. Technol. 60:17-23. Watkins, C.B. 2006. The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables. Biotechnol. Adv. 24:389-409. Watkins, C.B. 2007. The effect of 1-MCP on the development of physiological storage disorders in horticultural crops. Stewart Postharvest Rev. vol. 3, article 11. Watkins, C.B. 2008a. Overview of 1-methylcyclopropene trials and uses for edible horticultural crops. HortScience 43:86-94. Watkins, C.B. 2008b. Postharvest effects on the quality of horticultural products: using 1-MCP to understand the effects of ethylene on ripening and senescence processes. Acta Hort. 768:19-32. Watkins, C.B. 2008c. Postharvest ripening regulation and innovation in storage technology. Acta Hort. 796:51-58.

Watkins, C.B. 2010. Managing physiological processes in fruits and vegetables with inhibitors of ethylene biosynthesis and perception. Acta Hort. 880:301-310. Watkins, C.B., H. James, J.F. Nock, et al. 2010. Preharvest application of 1-methylcyclopropene (1-MCP) to control fruit drop of apples, and its effects on postharvest quality. Acta Hort. 877:365-374.