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Ramón A. Arancibia, Jeffrey L. Main and Christopher A. Clark

Tip rot, or restricted end rot, is a new sweetpotato (Ipomoea batatas) disease/disorder in Mississippi with unknown etiology. Since pathogen isolations have been inconsistent, a relationship of this disorder with stress is proposed. This disease/disorder is manifested as a restricted lesion at or close to the proximal end of the storage root and appears after 2 to 4 weeks in storage. In many cases, the lesion necrosis expands internally. On-farm and research station studies with preharvest foliar applications of ethephon were conducted in Mississippi to determine the potential association of tip rot with ethephon-induced stress. In addition, the effects of ethephon rate and interval between application and harvest on tip rot were investigated. After 1 to 2 months in storage, tip rot incidence was observed mostly in storage roots from ethephon-treated plants. The increase in tip rot incidence was well correlated with ethephon rate. These results suggest that preharvest applications of ethephon trigger a response that results in the tip rot disorder.

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Xiang Wang, Ramón A. Arancibia, Jeffrey L. Main, Mark W. Shankle and Don R. LaBonte

Skinning or surface abrasion in sweetpotato [Ipomoea batatas (L.) Lam.] roots during harvest causes a substantial loss of marketable products in storage as a result of rots, loss of moisture, and simply unattractive marketable appearance. In 2008, 2010, and 2011, changes in skinning incidence/severity and skin lignin/suberin content in response to preharvest foliar applications of ethephon or defoliation/devining were investigated. Field-grown ‘Beauregard’ (B-14) sweetpotato plots were treated with ethephon at 0.84, 1.68, and 2.52 kg·ha−1 (based on the recommendations for tobacco) applied at 1, 3, and 7 days before harvest (DBH). Defoliated/devined treatments were applied at 0, 1, 3, and 7 DBH. Skinning incidence and severity were reduced with ethephon when applied 3 and 7 DBH in 2 of 3 years compared with 1 DBH. The force required to skin the storage root was measured at harvest in 2011 and it increased with defoliation/devining and ethephon applications at 3 and 7 DBH. Skin lignin/suberin was higher in roots from ethephon-treated plants but was weakly correlated (r = 0.51) with the force required to peel the skin. Ethephon applications also increased cortex phenolic content and either decreased or maintained skin phenolic content in storage roots compared with defoliated/devined treatments. These results suggest that skin set and/or skinning resistance in sweetpotato appears to be influenced by other factors in addition to skin lignification/suberization.

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Ramón A. Arancibia, Cody D. Smith, Don R. LaBonte, Jeffrey L. Main, Tara P. Smith and Arthur Q. Villordon

Consumption of sweetpotato (Ipomoea batatas) has increased in the past decade in part because of its nutritional and health attributes, and because of the availability and convenience of processed products. The sweetpotato processing industry is expanding and supplying more sweetpotato products than ever before. Unlike the medium-sized roots (U.S. no.1) preferred for fresh market, large (jumbo) roots is accepted and in certain cases desired by the processing industry, and overall yield is preferred over strict sizing requirements and aesthetic appeal. Therefore, this study investigated the yield increase and grade proportions in response to plant spacing and extension of the growing period to improve profitability of the production system. Experiments with ‘Beauregard’ and ‘Evangeline’ sweetpotato were conducted in Mississippi and Louisiana during 2010 and 2011. Treatments consisted of a combination of early and late planting date and delay in harvest, in-row plant spacing, and row width. Yield increase was inconsistent with delaying harvest and appears to depend on environmental conditions at harvest late in the season. Marketable yield was consistently greater in early plantings than late plantings. Yield of U.S. no.1 grade was unaffected by delaying harvest regardless of planting date. Delaying harvest in early plantings contributed to increase jumbo-sized roots and marketable yield. The economic assessment of delaying harvest in early plantings indicated a gain in net benefit either when hand harvested for fresh market or field run bulk harvested for processing. Row width and in-row plant spacing had only a marginal effect on yield of canner grade (small-sized roots). The economic assessment of changing plant density indicated no gain in net benefit, which indicates that choice of plant density can depend on other factors.