Florida produced 6.5 million t of sweet oranges [Citrus ×sinensis (L.) Osbeck] during the 2008–2009 harvest season from ≈200,000 ha (Florida Agricultural Statistics Service, 2010). More than 95% of this fruit is used to produce orange juice, making Florida the second largest orange juice producer in the world. Harvesting is the single largest cost associated with citrus production in Florida, accounting for up to 50% of the total cost of production (Muraro, 2009). This is in contrast with Brazil, the largest producer of orange juice in the world, where harvesting costs are much lower such that during the 2000–2001 harvest season, Brazilian citrus growers were able to deliver frozen concentrated orange juice to the port of Tampa, FL, for only $0.0757 more per pound soluble solids than Florida growers. This discrepancy in production costs has been a major driving force in Florida's efforts to develop mechanical harvesting technology (Florida Department of Citrus, 2010; Whitney, 1995).
Adoption of mechanical harvesting systems has been slow. During the 2008–2009 harvest season, less than 15,000 ha (7% of total acreage) of citrus was mechanically harvested in Florida (Florida Department of Citrus, 2009). A number of issues have contributed to the slow adoption of mechanical harvesting technology, including processor concerns about the quantity of debris mixed with mechanically harvested fruit (Spann and Danyluk, 2010), production manager concerns about the effects of mechanical harvesting on tree health (Li et al., 2005), and issues related to the late-season harvesting of ‘Valencia’ oranges (Melgar et al., 2010).
‘Valencia’ orange trees typically bloom in late February through March in Florida and the mature crop is harvested beginning in March and extending into mid-June. Thus, there is an overlap between the young growing fruit and mature fruit. Studies have shown a significant reduction in the subsequent year's yield when ‘Valencia’ orange trees are mechanically harvested after ≈1 May (Hedden et al., 1984; Roka et al., 2005; Whitney, 1975). This is approximately the point when the young developing fruit have obtained a large enough size (≈2.5 cm diameter) and mass that they will be removed by the canopy shaker mechanism along with the mature fruit. Because of the ever-growing demand for not-from-concentrate (NFC) orange juice, processors require that growers hold fruit on the trees later into the season to provide fresh fruit as long as possible. Thus, efforts have been underway to find a viable way to harvest ‘Valencia’ orange fruit after 1 May without impacting subsequent year yields.
The abscission agent CMNP effectively loosens mature citrus fruit without affecting immature fruit, allowing mechanical harvest of ‘Valencia’ orange fruit after 1 May without impacting subsequent year yields (Burns et al., 2006). However, CMNP can sometimes cause peel injury consisting of a brown ring of depressed flavedo tissue around the stylar end of fruit where the CMNP spray solution accumulates (Alferez et al., 2006). This injury, commonly referred to as peel scarring, is associated with phospholipase A2 (PLA2) activity and can be prevented by inhibiting PLA2 with aristolochic acid (Alferez et al., 2006). No further characterization of this scarring has been conducted and processors are concerned that it may reduce peel integrity and/or increase fruit decay before processing.
In Florida, harvested oranges for processing are transported to the processing plant in open-topped semitrailers that hold 27 t of fruit. Fruit are stored until processing in these trailers under ambient conditions. Generally, fruit are transported from the orchard to the processing plant the day of harvest and are processed within 24 h. However, processors are concerned that fruit treated with CMNP, because of the scarring that can occur, may have weaker peels and be more susceptible to damage during transport and storage or may begin to decay more quickly than untreated fruit.
Our objective was to determine if fruit treated with CMNP and subjected to mechanical harvesting have reduced peel integrity, measured as peel puncture force and fruit crush force, or are more susceptible to postharvest decay within the commercial timeframe of normal harvest to processing.
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