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.
BanT.KugishimaM.OgataT.ShiozakiS.HoriuchiS.UedaH.2007Effect of ethephon (2-chloroethylphosphonic acid) on the fruit ripening characteristics of rabbiteye blueberrySci. Hort.112278281
BukovacM.J.1979Machine-harvest of sweet cherries: Effect of ethephon on fruit removal and quality of the processed fruitJ. Amer. Soc. Hort. Sci.104289294
BurnsJ.K.BukerR.S.RokaF.M.2005Mechanical harvesting capacity in sweet orange is increased with an abscission agentHortTechnology15758765
BurnsJ.K.FergusonL.GlozerK.KruegerW.H.RosecranceR.C.2008Screening fruit loosening agents for black ripe processed table olivesHortScience4314491453
DekazosE.D.1976Effects of preharvest applications of ethephon and SADH on ripening, firmness and storage quality of rabbiteye blueberries (cv ‘T-19’)Proc. Fla. State Hort. Soc.89266270
Gonzalez-HerranzR.CathlineK.A.FidelibusM.W.BurnsJ.K.2009Potential of methyl jasmonate as a harvest aid for ‘Thompson Seedless’ grapes: Concentration and time needed for consistent berry looseningHortScience4413301333
HeY.FukushigeH.HildebrandD.F.GanS.2002Evidence supporting a role of jasmonic acid in arabidopsis leaf senescencePlant Physiol.128876884
HowellG.S.StergiosB.G.StackhouseS.S.BittenbenderH.C.BurtonC.L.1976Ethephon as a mechanical harvesting aid for highbush blueberries (Vaccinium austral Small)J. Amer. Soc. Hort. Sci.101111115
KenderW.J.HartmondU.BurnsJ.K.YuanR.C.PozoL.2001Methyl jasmonate and CMN-pyrazole applied alone and in combination can cause mature orange abscissionSci. Hort.88107120
MalladiA.BurnsJ.K.2008CsPLDα1 and CsPLDγ1 are differentially induced during leaf and fruit abscission and diurnally regulated in Citrus sinensisJ. Expt. Bot.5937293739
SaniewskiM.UrbanekH.SzapskiJ.1987Effects of methyl jasmonate on ethylene production, chlorophyll degradation, and polygalacturonase activity in tomatoesJ. Plant Physiol.127177181
TakedaF.KrewerG.AndrewsE.PetersonD.L.MullinixJ.2008Assessment of v45 over-the-row mechanical harvester on pruned rabbiteye and southern highbush blueberryHortTechnology18130138
UedaJ.KatoJ.1980Isolation and identification of a senescence-promoting substance from wormwood (Artemisia absinthium L.)Plant Physiol.66246249
U.S. Department of Agriculture1995United States standards for grades of blueberries. Agricultural Marketing Service Washington DC
U.S. Department of Agriculture2012Non-citrus fruits and nuts 2011 summary. National Agricultural Statistics Service Washington DC
van DalfsenK.B.GayeM.M.1999Yield from hand and mechanical harvesting of highbush blueberries in British ColumbiaAppl. Eng. Agr.15393398
WasternackC.2007Jasmonates: An update on biosynthesis, signal transduction and action in plant stress response, growth and developmentAnn. Bot. (Lond.)100681697
YuanR.C.BurnsJ.K.2004Temperature factor affecting the abscission response of mature citrus fruit and leaves to CMN-pyrazole and ethephon in ‘Hamlin’ orangesJ. Amer. Soc. Hort. Sci.129287293