Sweetpotato is a nutritious source of food. Orange-fleshed cultivars are rich in β-carotene and purple-fleshed cultivars are rich in anthocyanins, both of which are important dietary antioxidants (Teow et al., 2007; Wang et al., 2016). In the state of Hawai‘i, most sweetpotato production is on the east coast of Hawai‘i Island, where the purple-fleshed landrace Okinawan is grown and exported to the U.S. mainland.
Sweetpotato production in Hawai‘i increased 7-fold between 2002 and 2011 from 2.3 million pounds to 16.7 million pounds and a farm gate value from $0.99 million to $7.3 million [Hawai‘i Department of Agriculture (HDOA), 2013, 2004]. This increased production was due largely to an increased export market after approval of quarantine treatments to control insect pests (Follett, 2006).
However, by 2016, area harvested for sweetpotato in Hawai‘i decreased from 1100 to 485 acres and farm gate value decreased to $1.18 million (HDOA, 2018). Problems that threaten the sustainability of the industry are as follows: 1) extreme offgrade shapes and sizes and inconsistencies in flesh color and 2) quarantine insect pests that negatively impact production and quality. A sweetpotato breeding program is needed in Hawai‘i to improve the consistency of shapes, sizes, and purple flesh color, as well as to improve resistance to insect pests.
The two major quarantine pests that adversely affect sweepotato production in Hawai‘i are sweetpotato weevil and sweetpotato vine borer [Omphisa anastomosalis (Follett, 2006)]. Sweetpotato weevil larvae feed and develop within the storage root of sweetpotato, making it difficult to control the larvae with insecticides and resulting in inedible storage roots (Thompson et al., 1999). Crop losses in Hawai‘i due to the sweetpotato weevil have been reported to range from 15% to 30% but could be as high as 60% to 97% if pest populations were not controlled (Valenzuela et al., 1994). Sweetpotato weevil is found worldwide and could cause crop losses of up to 80% (Nottingham and Kays, 2002).
Significant differences have been found among sweetpotato entries in resistance to injury of storage roots by insects, in particular by sweetpotato weevils of the genus Cylas (Jackson and Bohac, 2006; Jackson and Harrison, 2013; Jackson et al., 2012; Stathers et al., 2003a; Thompson et al., 1999). Resistance to sweetpotato weevils is likely a combination of antibiosis, tolerance, escape, and nonpreference (Stathers et al., 2003b). A poor correlation was found between results of laboratory studies (e.g., antibiosis studies and root choice) and those of field studies (Stathers et al., 2003b), demonstrating the importance of conducting cultivar trials in the field.
Most consumers in the United States prefer sweetpotatoes with sweet, moist, and orange flesh. ‘Beauregard’ is a popular, commercial, orange-fleshed cultivar grown in the United States (Jackson and Bohac, 2006; Jackson and Harrison, 2013). Unfortunately, it is susceptible to injury by several insects, including sweetpotato weevil (Jackson and Harrison, 2013; Jackson et al., 2012; Thompson et al., 1999). In Hawai‘i, consumers prefer sweetpotatoes with sweet, drier, purple flesh because they are familiar with the Okinawan landrace.
In a series of field trials at Pepe`ekeo, HI, we evaluated sweetpotato entries grown on Hawai‘i Island for yield of storage roots, resistance to insect pests, and quality. The overall goal was to identify alternative cultivars for commercial production, as well as superior sources of germplasm for breeding high-yielding, nutritious sweetpotatoes with tolerance to insect pests under tropical conditions.
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