Blueberry (Vaccinium spp.) is rapidly emerging as a major fruit crop in the United States with over 72,000 acres under cultivation and a crop valued at over $780 million U.S. in 2011 [U.S. Department of Agriculture (USDA), 2012]. Harvesting is a labor-intensive and expensive part of blueberry production. To decrease the costs associated with manual harvesting and to address issues with decreasing labor availability, there has been a renewed interest in exploring the use of mechanical harvesting. Mechanical harvesting is often associated with significant losses such as ground loss (≈20%), mechanical injury to the berries and the plant, removal of immature fruit, and decline in the post-harvest quality of the fruit (Takeda et al., 2008; van Dalfsen and Gaye, 1999). The application of fruit-loosening agents that can decrease the force required for fruit detachment can contribute greatly toward enhancing the efficiency of mechanical harvesting (Burns, 2002; Burns et al., 2005).
Abscission agents have been used in different fruit crops to decrease the FDF and to enhance the efficiency of mechanical harvesting. Ethephon (2-chloroethylphosphonic acid), an ethylene-releasing agent, has been extensively evaluated as a potential fruit-loosening agent in a wide range of fruit such as citrus (Citrus sinensis L.), grape (Vitis vinifera L.), olive (Olea europaea L.), and cherry (Prunus avium L.) (Bukovac, 1979; Burns, 2002; Burns et al., 2008; Fidelibus et al., 2007; Yuan and Burns, 2004). In blueberry, ethephon has been evaluated previously in relation to its effects on concentrating fruit ripening and also as a potential mechanical harvest aid (Ban et al., 2007; Dekazos, 1976, 1978; Eck, 1970; Howell et al., 1976). Ethephon applications reduced the fruit removal force and allowed for a reduction in the mechanical harvester vibration frequency required for fruit removal (Howell et al., 1976). The effects of ethephon on fruit abscission in rabbiteye and southern highbush blueberry have not been extensively evaluated, although the application of ethephon at 500 mg·L−1 was reported to result in some fruit drop in the rabbiteye blueberry cultivar, Tifblue (Dekazos, 1978). Also, the application of ethephon at 200 mg·L−1 was reported to have resulted in ≈33% fruit abscission by 7 d after treatment in ‘Tifblue’ (Ban et al., 2007).
Jasmonates are a group of compounds that include MeJa and its precursor, jasmonic acid, and are derived from the oxylipin pathway in plants. Jasmonates have diverse roles in plant growth and development and in plant responses to biotic and abiotic stress (Wasternack, 2007). Methyl jasmonate has been evaluated as a potential abscission agent in several fruit crops (Burns et al., 2008; Fidelibus et al., 2007; Gonzalez-Herranz et al., 2009; Hartmond et al., 2000; Kender et al., 2001). The application of MeJa, alone and in combination with other abscission agents, resulted in fruit abscission in sweet orange (Hartmond et al., 2000; Kender et al., 2001). Methyl jasmonate was also effective in reducing FDF and inducing fruit abscission in grapes (Fidelibus et al., 2007; Gonzalez-Herranz et al., 2009). Additionally, coronatine, a naturally produced compound with functional properties similar to the jasmonates, induced fruit abscission in citrus (Burns et al., 2003). The effects of MeJa on fruit detachment in blueberry have not been reported previously.
The main objective of this research was to determine the potential of ethephon and MeJa to induce fruit detachment in rabbiteye and southern highbush blueberry. To address this objective, the effects of different concentrations of ethephon and MeJa on fruit abscission and FDF were evaluated in multiple blueberry genotypes.
Ban, T., Kugishima, M., Ogata, T., Shiozaki, S., Horiuchi, S. & Ueda, H. 2007 Effect of ethephon (2-chloroethylphosphonic acid) on the fruit ripening characteristics of rabbiteye blueberry Sci. Hort. 112 278 281
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., Ferguson, L., Glozer, K., Krueger, W.H. & Rosecrance, R.C. 2008 Screening fruit loosening agents for black ripe processed table olives HortScience 43 1449 1453
Burns, J.K., Pozo, L.V., Arias, C.R., Hockema, B., Rangaswamy, V. & Bender, C.L. 2003 Coronatine and abscission in citrus J. Amer. Soc. Hort. Sci. 128 309 315
Dekazos, E.D. 1976 Effects of preharvest applications of ethephon and SADH on ripening, firmness and storage quality of rabbiteye blueberries (cv ‘T-19’) Proc. Fla. State Hort. Soc. 89 266 270
Dekazos, E.D. 1978 Maturity and quality responses of ‘Tifblue’ rabbiteye blueberries to SADH and ethephon Proc. Fla. State Hort. Soc. 91 168 170
Fidelibus, M.W., Cathline, K.A. & Burns, J.K. 2007 Potential abscission agents for raisin table and wine grapes HortScience 42 1626 1630
Gonzalez-Herranz, R., Cathline, K.A., Fidelibus, M.W. & Burns, J.K. 2009 Potential of methyl jasmonate as a harvest aid for ‘Thompson Seedless’ grapes: Concentration and time needed for consistent berry loosening HortScience 44 1330 1333
Hartmond, U., Yuan, R.C., Burns, J.K., Grant, A. & Kender, W.J. 2000 Citrus fruit abscission induced by methyl-jasmonate J. Amer. Soc. Hort. Sci. 125 547 552
He, Y., Fukushige, H., Hildebrand, D.F. & Gan, S. 2002 Evidence supporting a role of jasmonic acid in arabidopsis leaf senescence Plant Physiol. 128 876 884
Howell, G.S., Stergios, B.G., Stackhouse, S.S., Bittenbender, H.C. & Burton, C.L. 1976 Ethephon as a mechanical harvesting aid for highbush blueberries (Vaccinium austral Small) J. Amer. Soc. Hort. Sci. 101 111 115
Kender, W.J., Hartmond, U., Burns, J.K., Yuan, R.C. & Pozo, L. 2001 Methyl jasmonate and CMN-pyrazole applied alone and in combination can cause mature orange abscission Sci. Hort. 88 107 120
Malladi, A. & Burns, J.K. 2008 CsPLDα1 and CsPLDγ1 are differentially induced during leaf and fruit abscission and diurnally regulated in Citrus sinensis J. Expt. Bot. 59 3729 3739
Saniewski, M., Urbanek, H. & Szapski, J. 1987 Effects of methyl jasmonate on ethylene production, chlorophyll degradation, and polygalacturonase activity in tomatoes J. Plant Physiol. 127 177 181
Takeda, F., Krewer, G., Andrews, E., Peterson, D.L. & Mullinix, J. 2008 Assessment of v45 over-the-row mechanical harvester on pruned rabbiteye and southern highbush blueberry HortTechnology 18 130 138
Ueda, J. & Kato, J. 1980 Isolation and identification of a senescence-promoting substance from wormwood (Artemisia absinthium L.) Plant Physiol. 66 246 249
U.S. Department of Agriculture 1995 United States standards for grades of blueberries. Agricultural Marketing Service, Washington, DC
U.S. Department of Agriculture 2012 Non-citrus fruits and nuts 2011 summary. National Agricultural Statistics Service, Washington, DC
van Dalfsen, K.B. & Gaye, M.M. 1999 Yield from hand and mechanical harvesting of highbush blueberries in British Columbia Appl. Eng. Agr. 15 393 398
Wasternack, C. 2007 Jasmonates: An update on biosynthesis, signal transduction and action in plant stress response, growth and development Ann. Bot. (Lond.) 100 681 697
Yuan, R.C. & 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