Olive oil production is mainly located around the Mediterranean Basin and some others areas of Mediterranean climate (e.g., Australia, Argentina, California, Chile). Hand harvesting of olives (Olea europaea L.) for oil represents more than 50% of their total production cost (Barranco et al., 2004; Tous and Romero, 1992). Although mechanical continuous harvesting is quite efficient in many high-density orchards, olive tree shakers are normally much less efficient in traditional orchards with large trees and in some cultivars (Pastor et al., 2001; Tous et al., 2007). Lavee et al. (1982) suggested that shaker efficiency also depends on maturity stage, fruit load, and especially cultivar characteristics. ‘Arbequina’ is the most important olive variety grown in traditional Catalan orchards. This cultivar is characterized by small fruits and a weeping-open growing habit that reduces the energy transmitted through trunk vibration to the fruit (Tous and Romero, 1992).
The use of ethylene-releasing chemicals to increase removal rates of mechanical shakers has been widely studied in many countries and for many years (Lavee and Haskal, 1975; Martin et al., 1981; Tous et al., 1995; Vitagliano, 1975). However, removal efficiency in research trials using ethylene-releasing chemicals has been erratic (Martin et al., 1981), perhaps as a result of the variability in loosing product uptake and breakdown under natural conditions (Denney and Martin, 1994; Lavee and Haskal, 1975). In addition, environmental factors, including temperature, relative humidity (RH), and plant stress, have a great influence on the ethephon response (Klein et al., 1978; Martin et al., 1981).
Ethephon causes leaf abscission, which can compromise the next year’s production if more than 15% to 20% of the leaves are lost (Martin et al., 1981). Leaves also have different thresholds of sensitivity according to their maturity; mature leaves (25 to 28 months old) respond faster to external ethylene application than younger ones (Goren et al., 1998). Furthermore, olive fruits and leaves exhibit different thresholds of sensitivity and different absorption and diffusion rates when exposed to exogenous ethylene (Blumenfeld et al., 1978; Denney and Martin, 1994; Lang and Martin, 1985). Lang and Martin (1989) reported that low ethylene concentration could reduce leaf abscission with an acceptable degree of fruit loosening, but for several cultivars, this would not be enough to guarantee efficient and economical mechanical harvesting. Many compounds, other than ethylene, have also been studied as loosening agents for olive fruits, but many proved less efficient at reducing the force required for fruit removal (Barranco et al., 2004; Ben-Tal, 1987; Burns et al., 2008; Denney and Martin, 1994; Hartmann et al., 1976; Martin et al., 1981). Banno et al. (1993) demonstrated that a foliar spray treatment with phosphorus-containing compounds causes olive fruit abscission with minimal leaf loss. In addition, phosphorus compounds act independently of endogenous ethylene action in inducing leaf abscission in olive trees (Goren et al., 1998; Yamada and Martin, 1994). It has recently been reported that applying MKP alone, or in combination with ethephon, reduces the fruit removal force of olives (Barranco et al., 2004; Burns et al., 2008). Taken as a whole, these studies suggest that each ethephon–P compound combination needs be tested at each site as a result of the great influence that environmental conditions have over obtaining maximum shaking efficiency with minimum defoliation.
The objective of this study was to evaluate the potential of ethephon (2-chloroethyl phosphonic acid) in combination with P formulation compounds as an agent for loosening olive fruits and improving the efficiency of the mechanical harvesting of mature ‘Arbequina’ olive trees under the typical environment conditions found in Catalonia.
Banno, K., Martin, O., Navarro, G.C. & Carlson, R.M. 1993 The role of phosphorus as an abscission-inducing agent for olive leaves and fruit J. Amer. Soc. Hort. Sci. 118 599 604
Burns, J.K., Ferguson, L., Glozer, K., Krueger, W.H. & Rosecrane, R.C. 2008 Screening fruit loosening agents for black ripe processed table olives HortScience 43 1449 1453
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