Production and consumption of sweetpotatoes has steadily increased in recent years as recognition of their benefits to a healthy diet and availability of more diverse products has increased (U.S. Department of Agriculture, 2011). The need to continually supply both fresh and processing markets has increased simultaneously, resulting in increased need to store sweetpotatoes for up to 1 year. Given the high cost of both production and storage of sweetpotatoes, it is essential for producers to pack out as great a proportion of the stored sweetpotatoes as possible. Sweetpotatoes are routinely cured immediately after harvest by holding them for 4 to 7 d at 85 °F and 90% relative humidity (RH) to promote healing of wounds incurred during harvest, thus reducing microbial infection and water loss during storage (Clark et al., 2013a). In addition, recent research suggests that chemical defoliation before harvest may increase skin adherence and reduce skinning during harvest and subsequent handling (Schultheis et al., 2000; Wang et al., 2013).
In the past 5 to 10 years, two problems have emerged in some locations that have seriously reduced pack-out efficiency: end rots and internal necrosis. The end rot complex includes aggressive rots progressing from either the proximal or the distal end of the root or both and a more restricted tip rot that appears in storage near the proximal end of the root (Arancibia et al., 2013; Clark et al., 2013a). Various fungi have been isolated from each type of lesion from affected roots including species of Fusarium that are not recognized as plant pathogens, as well as recognized sweetpotato pathogens including Fusarium solani, Macrophomina phaseolina, Lasiodiplodia theobromae, and Diaporthe batatatis (da Silva and Clark, 2012; Stokes et al., 2012). These fungi have also been isolated frequently from symptomless transplants and storage roots and it appears that infection is not a limiting factor to the development of this disease complex (da Silva, 2013). Internal necrosis appears as brown to black discolored areas that develop during storage near the proximal end of storage roots and the symptoms are predominantly internal and not apparent unless the root flesh is cut to expose the internal tissue. Since no microorganisms are consistently associated with internal necrosis, it is believed to be a physiological disorder (Jiang, 2013; Schultheis et al., 2009).
From recent studies and anecdotal observations from growers, two factors have been suggested to increase the incidence of both end rots and internal necrosis. Flooding in the field shortly before harvest has been suggested to increase both problems as has use of ethephon when used to kill vines before harvest (Arancibia et al., 2013; Dittmar et al., 2010). Cultivars may also vary in susceptibility to both disorders, but this hypothesis has not been investigated. This study was undertaken to determine the susceptibility of major sweetpotato cultivars and advanced breeding lines to the end rot complex and internal necrosis with or without the use of ethephon as a vine killer before harvest, and also to determine the effect of curing on incidence and severity of both disorders. The primary goal of the study was to determine if sweetpotato breeders could use ethephon treatment and curing manipulations as screening tools for new genotypes for their susceptibility to the end rot complex and/or internal necrosis.
Arancibia, R.A., Main, J.L. & Clark, C.A. 2013 Sweetpotato tip rot incidence is increased by preharvest applications of ethephon and reduced by curing HortTechnology 23 288 293
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Wang, X., Arancibia, R.A., Main, J.L., Shankle, M.W. & LaBonte, D.R. 2013 Preharvest foliar applications of ethephon increases skin lignin/suberin content and resistance to skinning in sweetpotato storage roots HortScience 48 1270 1274