Highbush blueberries grown for fresh market are typically hand harvested; however, hand harvesting is labor intensive and costly, resulting in low production efficiency and profitability (Takeda et al., 2008, 2013). In addition, unpredictable labor supplies affect a large number of specialty crops, and are becoming a major issue in blueberry production (Zhang and Wilhelm, 2011). To decrease harvesting costs in blueberry production, mechanical harvesters have been developed, tested, and manufactured since the late 1950s (Hedden et al., 1959; Peterson and Brown, 1996; Takeda et al., 2008, 2013; van Dalfsen and Gaye, 1999), but have been primarily used to harvest berries for processing or at the end of the harvest season (Williamson et al., 2012; Yu et al., 2012). However, growers’ concerns about hand-harvesting costs and labor availability have increased interest in adopting mechanical harvesters for fresh market blueberries. Brown et al. (1996) reported an increase of ≈60-fold in labor efficiency and a cost reduction of ≈85% when using over-the-row mechanical blueberry harvesters. However, mechanical harvesting causes excessive fruit bruising (Sargent et al., 2013) and harvest losses. Bruising occurs when berries hit canes, other fruits, and interior surfaces of the harvester or catch plates while falling through the bush after detachment (Takeda et al., 2008), and as fruit moves from the catch plates to the lugs (Yu et al., 2012). Harvest losses may occur due to harvesting of unripe or damaged berries, reducing packout efficiency by 4% to 30% (Peterson and Brown, 1996; Takeda et al., 2013; van Dalfsen and Gaye, 1999). Harvest losses may also occur due to the design of the machine, which allows berries to fall to the ground because the catch plates do not fit closely around the multicaned crown of the bush. Estimates of ground losses from mechanical harvesting range from 10% to 50% of the total fruit harvested (Brown et al., 1996; Peterson and Brown, 1996).
Blueberries are very perishable (Vicente et al., 2007), thus, adequate and efficient harvesting methods (Sargent et al., 2013), handling and packing (Jackson et al., 1999), and postharvest storage strategies (Schotsmans et al., 2007) are needed to increase the storage and shelf life of fresh blueberries. Several studies have compared fruit quality of mechanical- vs. hand-harvested blueberry fruit immediately after harvest and during postharvest storage. The increased fruit bruising associated with mechanical harvest reduces berry firmness compared with hand harvest (Li et al., 2011). During postharvest storage, mechanical-harvested berries exhibit a decrease in overall appearance, fresh weight, and firmness, and an increase in shriveling (Sargent et al., 2013) and respiration (Nunez-Barrios et al., 2005) compared with hand-harvested berries. Efficient harvesting systems are needed to reduce fruit losses during harvest and maintain good fruit quality during postharvest storage, since fresh-market berries must maintain acceptable fruit quality for 2 or 3 weeks after harvest (Sargent et al., 2013).
Vaccinium arboreum is a wild species native to the southeastern United States that exhibits a single-trunk growth habit (Brooks and Lyrene, 1998). If used as a rootstock for cultivated Vaccinium, the monopodial tree-like architecture of V. arboreum could improve mechanical harvesting efficiency of blueberries. A blueberry plant with a single trunk could eliminate much of the yield losses that occur with multicaned plants, as well as reduce the need to prune the bushes to fit the harvest machines. Along with the desired characteristics for mechanical harvesting, V. arboreum tolerates high pH (above 6.0) and low organic matter soils (below 2.0%) (Brooks and Lyrene, 1998), conditions that cultivated V. corymbosum tolerates poorly. Thus, it may be useful in reducing use of soil amendments that are necessary for successful blueberry production in many areas.
Although there is currently research investigating mechanical vs. hand harvesting of blueberry, there are no reports of studies comparing grafted vs. own-rooted plants to assess yield losses due to mechanical harvesting. Further, there are no other reports examining the potential of using V. arboreum as a rootstock to reduce or eliminate soil amendments while maintaining yield and postharvest fruit quality in blueberry.
The hypotheses tested in the present research are that 1) yield and fruit quality at harvest and during postharvest storage of hand- or mechanical-harvested grafted SHB are greater compared with own-rooted SHB and 2) fruit ground losses during harvest are decreased in grafted plants that are mechanical harvested compared with mechanical-harvested own-rooted plants. The specific objectives were to evaluate the effects of root (own rooted vs. grafted), soil (amended vs. nonamended), and harvest method (hand vs. mechanical) treatments on marketable fruit yield, berry weight, harvest losses, and berry quality at harvest and during postharvest storage.
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