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Sylvia M. Blankenship and Michael D. Boyette

`Beauregard', `Jewel', `Hernandez', `Carolina Rose', and `White Delight' sweetpotato [Ipomoea batatas (L.) Lam.] roots were placed in chambers for curing at 30 °C and 50%, 70%, or 85% relative humidity (RH) for 1 week. Uncured roots were held at 15 °C and 90% RH. After curing, roots were removed temporarily from the chambers, and chamber conditions were reset for the following storage treatments: 15 °C/85% RH; 18 °C/70% RH; and 18 °C/50% RH. Roots were stored 3 to 4 weeks. Experiments were in factorial arrangements so all combinations of curing and storage conditions were present. Experiments were conducted in two seasons. Roots were subjected to a pressurized water jet and the amount of skinning that occurred was visually rated several times during curing and storage. Weight loss was measured in `Beauregard'. Susceptibility to skinning changed over time and with the temperature and humidity conditions. Curing at 30 °C and any humidity between 50% and 85% generally improved epidermal adhesion, but there were exceptions. Lower humidities promoted greater weight loss. Epidermal adhesion changed during storage, becoming both stronger and weaker, indicating that sweetpotato epidermis is in an active state even after curing. The standard curing and storage conditions of 30 °C/85% RH and 15 °C/85% RH, respectively, are still a reasonable practice.

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Luz Reyes*, Sylvia M. Blankenship*, Jonathan R. Schultheis*, and Michael D. Boyette

Sweetpotato roots, especially the cultivar Beauregard, tend to experience epidermal loss during harvest and postharvest handling which results in a less attractive product in the market. A survey study was conducted among North Carolina (N.C.) sweetpotato growers in Fall 2001 and 2002. The purpose of the survey was to gather information and try to correlate cultural practices, growing conditions and site characteristics with the occurrence of attractive roots and to define new scientific approaches to reducing epidermal loss. Samples were obtained from 42 N.C. farms. Survey field information and laboratory results were correlated to identify possible factors affecting the appearance of the roots. 1300 roots were used to measure skin adhesion, peeling susceptibility, skin moisture, skin anthocyanin and lignin content. From survey questions, 50 characteristics were defined for each sample, according to field characteristics, cultivar information, cultural practices and harvest and postharvest practices. Statistical analyses were performed to determine the relationship between the skin characteristics analyzed at the laboratory, and the survey descriptors information. Analysis of variance was used for laboratory data analysis. Person correlations were made between survey variables and laboratory characteristics. Several possible relationships between root appearance and other characteristics/practices were identified. Root skin adhesion may improve in later generations from elite propagation material. Early application of phosphate and potash fertilizers were correlated to improved root skin adhesion. There appeared to be a relationship between soil moisture at harvest time, increased lignin content in the skin and peeling susceptibility. Future areas of study were identified.

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Jonathan R. Schultheis, Sylvia M. Blankenship, David W. Monks, and Michael D. Boyette

The `Beauregard' sweetpotato variety is very prone to damage to its skin. We evaluated several preharvest treatments to reduce skinning so that less damage was done at harvest, during transport, and packing. Three field tests were conducted in 1998 (two tests) and 1999 (one test) in North Carolina. Treatments were implemented 1 and 2 weeks prior to harvest and were either chemical or mechanical. The three mechanical treatments were flail mowing, flail mowing and barring off, and vine snatching. The following chemical treatments were made: PREP, Diquat, Dessicate II, and 2,4-D at various rates. Sweetpotatoes were harvested and roots were graded. Subsequently, U.S. No. 1 root subsamples were obtained from each plot in order to evaluate the effects of treatment on skin tightening of roots. Roots were evaluated from each plot for skin toughness using a “skin-o-meter” where a pressurized stream of water was directed at a sweetpotato. The roots were then evaluated for skinning by checking if the skin was broken using the skin-o-meter. A second method was used to evaluate the effect of treatment for its effect on skin tightening (reduced skinning). One bushel of roots from each treatment plot was transported to Clinton, N.C., and run through a small packing line at the Horticultural Crops Research Station the next day after harvest. The sweetpotatoes were then evaluated in Raleigh for the number of incidences where skin had been removed during the harvesting, transport, or packing process. The severity of skinning was characterized by counting the number of small (<5 mm), medium (width 5-10 mm) and large (width 10+ mm) skinned areas on a root. An overall appearance rating for roots was also recorded for each subsampled plot with 10 being the best rating and 1 being the worst. Results indicate that treatment 14 days prior to harvest rather than 7 days prior to harvest seems to be advantageous in most cases for reducing skinning and maintaining yield of sweetpotato when compared with not treating the vines. Regardless of whether the treatment was chemical or mechanical, treatments were apparently beneficial in these tests. Application of PREP 7 days prior to harvest resulted in sweetpotatoes with the most resistance to skinning in 1999, the fewest large-size skinning abrasions on roots, and best appearance. PREP shows promise as a means to reduce skinning in sweetpotatoes, but presently is not labeled for use on sweetpotatoes.

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Sergio J. Carballo, Sylvia M. Blankenship, Douglas C. Sanders, David F. Ritchie, and Michael D. Boyette

Commercial packing lines in Sampson County, N.C., were surveyed during two growing seasons to study handling methods on susceptibility of bell pepper fruits (Capsicum annuum L.) to bacterial soft rot (Erwinia carotovora subsp. carotovora). Samples were taken from two field packers and one packing house in 1991 and from two field packers and four packing houses in 1992. One field packer and one packing house were common to both years. Fruits were either inoculated with bacteria or untreated and stored at 10 or 21C. Damaged fruits were counted and classified as crushed, cut, bruised, abraded, and other injuries. Fruit injury was less dependent on whether the operation was a packing house or a field packing line than on the overall handling practices of the individual grower. In general, packing peppers in packing houses resulted in an increased number of bruises, whereas fruit from field packing lines had more abrasions. More open skin injuries resulted in greater fruit decay. In both years, fruits stored at 10C had less top rot than fruits stored at 21C. In 1992, they also had less pod rot. Dry and chlorinated lines often had equivalent rot problems.

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Chen Jiang, Penelope Perkins-Veazie, Sylvia M. Blankenship, Michael D. Boyette, Zvezdana Pesic-VanEsbroeck, Katherine M. Jennings, and Jonathan R. Schultheis

A series of studies were conducted to better understand the occurrence and causes of internal necrosis (IN) in ‘Covington’ sweetpotato (Ipomoea batatas). Assessment of the problem among the industry was done for 2 years and revealed that IN was widespread in commercial storage facilities throughout the state of North Carolina; both incidence and severity were generally low (<10% incidence with minimal severity of symptoms). A few storage rooms had a high percentage of IN with severe storage root symptoms but results were inconsistent across years and among rooms. Preharvest studies with commercially used insecticides did not induce IN, but the harvest aid ethephon consistently induced IN with an incidence higher than 50%. Internal necrosis symptoms were not detectable at harvest, and earliest consistent incidence was observed 6 days after harvest (DAH) during the curing phase. Symptoms became more prevalent and severe at 30 DAH. However, in commercial storage rooms, no relationship was found between IN incidence and postcuring storage temperature or relative humidity (RH) conditions. Sweetpotato storage roots stored in air-tight barrels and exposed to 100 ppm ethylene after curing showed no relationship between the presence of ethylene gas in storage and incidence of IN. Our results indicate that IN incidence of ‘Covington’ is erratic with no obvious cause among storage rooms and that initiation of IN may occur most frequently during the first week following harvest.

Open access

Fernando Montero de Espinosa Baselga, Jonathan R. Schultheis, Michael D. Boyette, Lina M. Quesada-Ocampo, Keith D. Starke, and David W. Monks

Internal necrosis (IN) is a physiological disorder that affects Covington, the most commonly grown sweetpotato (Ipomoea batatas) cultivar in North Carolina. Because IN affects the quality of sweetpotato storage roots, studies have been conducted since the first report of IN in 2006. Field studies (three in 2016 and two in 2017) were conducted to evaluate preharvest and postharvest treatments on the occurrence of IN in ‘Covington’ storage roots. Four preharvest treatments consisted of combinations of high chlorine or minimal chlorine potash fertilizer and mowing vs. not mowing before harvest. For postharvest treatments, 30 storage roots were obtained at harvest from each preharvest treatment plot and immediately cured in 75 and 85 °F rooms for a duration of 0.5, 1, 2, 3, and 5 weeks in 2016, and 0.5, 1, and 2 weeks in 2017. Shorter curing durations (0.5 and 1 week) coincided with industry recommendations while longer durations mimicked the challenges that some commercial facilities face when cooling down temperatures of rooms after curing is supposed to be concluded. Once curing temperature and curing duration treatments were completed, roots were placed in a 58 °F storage room at 85% relative humidity until cut. A control comparison was included in which harvested roots were placed in a 58 °F storage room (no curing) immediately after harvest. The storage roots from all temperature treatments were then cut 49 to 80 days after harvest, and incidence and severity of IN visually rated. Preharvest potash fertilizer treatments had minimal or no effect on occurrence of IN. However, mowing vines before harvest in several studies reduced IN incidence when roots were cured for more than 0.5 week at temperatures of at least 75 °F. Lower temperature (75 vs. 85 °F) and shorter curing duration (0.5 vs. 1, 2, 3, or 5 weeks) resulted in reduced IN occurrence in ‘Covington’ sweetpotato.