Mechanical harvesting of citrus fruit for juice processing from large-scale commercial plantings in Florida has economic advantages (Roka et al., 2008) over hand-harvesting, especially when adequate seasonal labor is not available (Brown, 2005; Roka, 2004). The shaking and visible injuries that citrus trees may experience during MH with trunk or canopy shakers are considered major impediments to the widespread adoption of MH (Li and Syvertsen, 2005; Zekri and Syvertsen, 2008). However, bark and branch injuries by canopy shakers are often not worse than injuries from ladders during hand picking operations (Buker et al., 2004), and there tends to be less leaf and twig loss from MH after the initial year of MH. The most common MH injuries in citrus and other fruit trees include leaf loss, twig loss, bark scuffing, flower loss, green immature fruit (fruitlet) drop, and exposure of roots at the soil surface (Halderson, 1966). Nonetheless, there is no evidence that such injuries in healthy well-managed citrus trees lead to any tree loss or decrease in yield from either long-term MH (7 to 8 years; Hedden et al., 1988; Whitney, 1995) or any other physiological stress associated with MH when compared with hand-harvested trees (Li and Syvertsen, 2005). There is a continuing problem in late-season MH of ‘Valencia’ sweet orange, however, because fruitlets from the next season's crop may be large enough to be unavoidably removed by the harvesting machine (Burns et al., 2006). Although winter drought stress of ‘Valencia’ sweet orange trees can effectively delay flowering so that fruitlets are not large enough to be susceptible to MH (Melgar et al., 2010), there is concern that mechanical injury of fruitlets could lead to subsequent premature fruit drop or lower fruit quality. The effects of late-season MH injury to fruitlets of ‘Valencia’ sweet orange exposed to previous winter drought stress have not been described.
Oleocellosis, rindspot, or oil spotting of citrus fruit is a common injury of the flavedo (Fawcett, 1916) caused by mechanical injury from hail, wind, and improper handling (Brodrick, 1970; Cahoon et al., 1964; Dodson, 1966). Mechanical injury allows phytotoxic essential oils (and terpenes) to leak out of oil glands and cause injury to surrounding flavedo cells resulting in oleocellosis. The injured superficial tissues dry out and form a thin, cracked scab on the surface of the fruit (Fawcett, 1916) and the injured rind may not continue to develop mature color, leaving a green or pale area where the injury occurred. Oleocellosis can appear on fruit as small as 2 to 3 cm in diameter (Jamieson et al., 2006) and appears to be greater on fruitlets than on fully colored or mature fruit. This may be a perception only because green damaged areas do not degreen and are more noticeable on fruitlets. We determined how MH affected green fruitlets from the next season's crop in late-harvested ‘Valencia’ sweet orange trees. We tested the hypothesis that different irrigation treatments from the previous winter would affect oleocellosis injury, subsequent fruitlet drop, and fruit quality at maturity.
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