Olives (Olea europaea L.) are commercially grown throughout the world in areas of Mediterranean climate. Cultivation is primarily for oil and table olive products. In the United States, California is the only state with commercial olive orchards and in 2000 to 2002 accounted for ≈7% of total world table olive production (Connell, 2005). The California olive industry relies almost exclusively on the table olive.
Table olives are harvested immature green at horticultural maturity but before physiological maturity (Ferguson et al., 2005). Harvest is done by hand labor over a period of ≈2 months. Increased labor costs and low labor availability have intensified industry interest in mechanical harvesting. Unusually low temperatures during flower bud initiation in Feb. 2006 in California's Central Valley olive production areas markedly reduced yield in a year when lower yield was expected as a result of alternate bearing. Extremely low yield combined with labor pressures increased harvesting costs further and strained olive inventories at the processing plant. To ensure future economic stability for the olive grower and consistent product flow at the processing plant, the California table olive industry has viewed the development of a successful mechanical harvesting system, that is, mechanical harvesting combined with abscission agent application (Burns et al., 2005), as a high priority.
Trunk-shaking mechanical harvesters were evaluated in the past but unable to harvest table olive fruit efficiently and without damage (Ferguson et al., 2005). Canopy-shaking mechanical harvesters are being developed currently and show promise. However, a fruit-specific abscission agent would allow for higher fruit removal. Moreover, an abscission agent would enable lower mechanical forces to be applied during harvest, thus minimizing fruit damage. Fruit damage is an industry concern because bruising may compromise quality of the final canned product, although this remains to be tested.
Abscission agents were applied experimentally to olive canopies in the past to improve fruit removal by trunk-shaking mechanical harvesters (Martin, 1994). Of those tested, only ethylene-releasing compounds (ERCs) such as ethephon (2-chloroethyl phosphonic acid) achieved consistent fruit loosening (Hartmann et al., 1970; Martin et al., 1981). ERC use in many crops, including olive, has been problematic as a result of attendant leaf loss coincident with fruit loosening. Treatments designed to minimize unwanted defoliation such as calcium application (Martin et al., 1981), or alteration in ERC application timing and duration (Lang and Martin, 1985, 1989), were promising in a laboratory setting but unpredictable in the field (Martin, 1994). Recent work in Florida identified compounds that accelerated mature and immature fruit abscission when applied to citrus canopies in the field (Burns, 2002). In this work, we describe efficacy of several of these compounds and reevaluate the potential of ethephon for olive fruit loosening.
Banno, K., Martin, 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
Bukovac, M.J. 1979 Machine-harvest of sweet cherries: Effect of ethephon on fruit removal and quality of the processed fruit J. Amer. Soc. Hort. Sci. 104 289 294
Burns, J.K., Buker, R.S. & Roka, F.M. 2005 Mechanical harvesting capacity in sweet orange is increased with an abscission agent HortTechnology 15 758 765
Burns, J.K., Pozo, L.V., Arias, C.R., Hockema, B., Rangaswamy, V. & Bender, C. 2003 Coronatine and abscission in citrus J. Amer. Soc. Hort. Sci. 128 309 315
Connell, J.H. 2005 History and scope of the olive industry 1 10 Sibbett G.S., Ferguson L., Coviello J.L. & Lindstrand M. Olive production manual University of California Agriculture and Natural Resources Publication 3353
Ferguson, L., Klonsky, K. & Martin, G.C. 2005 The olive harvest 135 140 Sibbett G.S., Ferguson L., Coviello J.L. & Lindstrand M. Olive production manual University of California Agriculture and Natural Resources Publication 3353
Fidelibus, M.W., Cathline, K.A. & Burns, J.K. 2007 Identification of abscission agents for raisin, table and wine grapes HortScience 42 1626 1630
Goren, R., Huberman, M. & Martin, G.C. 1998 Phosphorus-induced leaf abscission in detached shoots of olive and citrus J. Amer. Soc. Hort. Sci. 123 545 549
Hartmann, H.T., Tombesi, A. & Whisler, J. 1970 Promotion of ethylene evolution and fruit abscission in the olive by 2-chloroethanephosphonic acid and cycloheximide J. Amer. Soc. Hort. Sci. 95 635 640
Hartmond, U., Yuan, R., Burns, J.K., Grant, A. & Kender, W.J. 2000 Citrus fruit abscission induced by methyl jasmonate J. Amer. Soc. Hort. Sci. 125 547 552
Lang, G.A. & Martin, G.C. 1985 Ethylene-releasing compounds and the laboratory modeling of olive fruit abscission vs. ethylene release J. Amer. Soc. Hort. Sci. 110 207 211
Lang, G.A. & Martin, G.C. 1989 Olive organ abscission: Fruit and leaf response to applied ethylene J. Amer. Soc. Hort. Sci. 114 134 138
Martin, G.C., Lavee, S. & Sibbett, G.S. 1981 Chemical loosening agents to assist mechanical harvest of olive J. Amer. Soc. Hort. Sci. 106 325 330
Pozo, L. & Burns, J.K. 2000 Ethylene action inhibitors reduced Ethrel-induced leaf drop and gummosis in citrus Proc. Intl. Soc. Citricult. IX Congr 1 578 579
Pozo, L., Yuan, R., Kostenyuk, I., Alferez, F., Zhong, G.Y. & Burns, J.K. 2004b Differential effects of 1-methylcyclopropene on citrus leaf and mature fruit abscission J. Amer. Soc. Hort. Sci. 129 473 478
Reed, N. & Hartmann, H.T. 1976 Histochemical and ultrastructural studies of fruit abscission in the olive after treatment with 2-chloroethyl-tris-(2-methoxy)-silane J. Amer. Soc. Hort. Sci. 101 633 637
Yuan, R. & Burns, J.K. 2004 Temperature factor affecting the abscission response of mature citrus fruit and leaves to CMN-pyrazole and ethephon in ‘Hamlin’ oranges J. Amer. Soc. Hort. Sci. 129 287 293
Zimmerman, D.C. & Coudron, C.A. 1979 Identification of traumatin, a wound hormone, as 12-oxo-trans-10-dodecenoic acid Plant Physiol. 63 536 541