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Alba J. Collart, Stephen L. Meyers, and Jason K. Ward

thin and easily sloughed off of storage roots during harvest, transport, packing, and stocking. At harvest, skinning injury can create entry points for postharvest plant pathogens and allow for increased water loss, often causing roots to shrivel

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Arthur Villordon, Jeffrey Cole Gregorie, Don LaBonte, Awais Khan, and Michael Selvaraj

in French fry processing, uniform, round-shaped storage roots are desirable to reduce nonuniform slices ( Hoque and Saha, 2017 ). Consistency in SRL also is desirable for increased mechanization, leading to overall reduced cost of production ( Tang et

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Rolland Agaba, Phinehas Tukamuhabwa, Patrick Rubaihayo, Silver Tumwegamire, Andrew Ssenyonjo, Robert O.M. Mwanga, Jean Ndirigwe, and Wolfgang J. Grüneberg

Yam bean is a legume that forms storage roots ( Sørensen, 1996 ). Roots and tubers produced by legumes have long been recognized as a good food source, and they have been recommended for human nutrition ( FAO, 1979 ). Nonetheless, the use of legume

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Jean B. Ristaino and Charles Averre

The effect of fibrous root infection by S. ipomoea on disease on storage roots and production of marketable yield in the susceptible sweetpotato cultivar `Jewel' was evaluated in field experiments in 3 years. Drip irrigation (main plots) reduced disease on fibrous roots in plots not treated with sulfur or fumigated, but did not significantly increase yields in any year. Sulfur (subplots) reduced the severity of the disease on fibrous roots in nonfumigated plots in 2 years, but reduced yields by 21-33% in 2 of 3 years. Fumigation of soil with Telone C-17 (sub-subplots) reduced the percentage of diseased storage roots produced per plot from 71%, 8%, and 22% in nonfumigated plots to 52%, 3% and 6% in fumigated plots in 1988, 1989 and 1990, respectively and reduced the severity of disease on fibrous roots in all years. Only fumigation increased the yield of marketable storage roots by 68% and 19% in two of three years. The severity of disease on fibrous roots was positively correlated with the percentage of diseased storage roots produced per plot (r = 0.84) and the number of diseased storage roots produced per plant (r = 0.64), and was negatively correlated with the number of storage roots produced per plant (r = -0.66). Yield of marketable storage roots was negatively correlated with both the severity of disease on fibrous roots (r = -0.77) and the percentage of diseased storage roots produced per plot (r = -0.73). These data demonstrate the importance of fibrous root disease in this pathosystem. Management strategies that reduce disease on fibrous roots may ultimately lead to increased yield of storage roots.

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Arthur Villordon, Don LaBonte, and Julio Solis

roots, and storage roots during the initial storage root bulking stage as determined using destructive sampling and scanner-based minirhizotron system in sweetpotatoes grown in Chase, LA. z Minirhizotron-based measurement of adventitious root development

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David Graper and Will Healy

Non flowering Alstroemeria `Regina' plants were divided into aerial components: stems and apical and basal leaves or underground components: rhizome, storage roots, stele and fibrous roots. Samples were collected from distal and proximal ends of the rhizome to allow comparisons between structures of different ages. Ethanol soluble sugars were extracted and measured using HPLC. Starch was degraded to glucose using amyloglucosidase and measured.

There were no age differences in the starch, total soluble sugar (TSUGAR) or total soluble carbohydrates (TCHO) in the rhizome or aerial portions of the plant. There was a preferential partitioning of starch, sucrose, TSUGAR and TCHO to underground plant parts. The storage roots were the primary sink for the stored carbohydrates. Stems contained large concentration of glucose while fructose was found in storage roots and old stems. Sucrose was found primarily in old steles and storage roots. Starch was partitioned almost exclusively into the storage roots with no difference due to age of the storage root. Up to 42% of the TCHO in the old storage roots was composed of a carbohydrate which co-chromatogramed with melezitose using HPLC.

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S.M.A. Crossman, M.C. Palada, and J.A. Kowalski

A study was conducted to evaluate the effect of irrigation on yield and sweetpotato weevil (SPW) infestation of sweetpotato storage roots. Sweetpotato was grown in plots under controlled soil moisture regimes. The treatments were rainfed (no applied irrigation) and irrigation applied to maintain soil moisture levels at 20, 40, and 60 kPa, based on tensiometer readings. The 40- and 60-kPa treatments produced the highest yield of root biomass. Irrigation applied at 40 kPa produced significantly more medium-sized storage roots (8.1 t·ha–1) than the rain-fed treatment, which produced 4.4 t·ha–1. All of the irrigation treatments produced significantly more marketable storage roots with a lower mean damage index (MDI) than the rain-fed treatment. There was an inverse relationship between MDI and soil moisture levels among the irrigation treatments. A significantly higher percentage of storage roots (51.5%) from the 20-kPa treatment were rated in the Damage Index (DI)-1 (uninfested roots) category than from the rain-fed treatment (27.7%). Additionally, the percentage (29.4%) of storage roots from the rain-fed treatment rated in the DI-6 (most severe) category was significantly higher than the applied irrigation treatments, with 13.9%, 13.9%, and 6.0% respectively, for the 60-, 40-, and 20-kPa treatments. Irrigation therefore has potential to increase sweetpotato yields while reducing SPW infestation levels.

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Sharon R. Funderburk and Wanda W. Collins

Crimson clover Trifolium incarnatum L.) was used as a N source for sweet potato [Ipomoea batatas (L.) Lam.]. Treatments were designed to compare estimated N delivery by clover incorporation amounts of N delivered by inorganic fertilizer. Plants were sampled every 14 days and sectioned into four parts: shoots, stem tips, fibrous and storage roots. Dry matter content was significantly influenced by time. Total plant dry matter was lowest in the highest inorganic N treatment. Nitrogen concentration (DWB) decreased over time and was highest in the highest inorganic N treatment. Similar vine weights were noted in N and clover treatments while number of storage roots per plant was unaffected by treatment as was weight per storage root, which increased linearly over time. No significant difference existed between the high and low N application treatment or late clover incorporation treatment in any grade of storage roots except culls, which were 90% lower in clover treatments than in N fertilizer treatments.

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R. C. Sloan Jr., P. G. Thompson, W. B. Burdine Jr., J. L. Main, and P. D. Gerard

`Beauregard' storage roots which were discarded from the Mississippi sweetpotato foundation seed program because of the presence of flesh mutations were bedded in Spring 1991. After the plants were pulled from the roots, the roots were further examined, and the flesh mutations were characterized by size and frequency. The progency from the original roots were examined for flesh mutations for three generations in 1991, 1992, and 1993. The degree of mutation in the original root did not influence the degree of mutation in succeeding generations of storage roots. In 1992 and 1993, the degree of mutation in the third and fourth generation roots did not differ from that of storage roots grown from plants from the foundation seed plant beds.

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Yan Wang and Stanley J. Kays

The sweetpotato weevil (SPW) [Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae)] is the single most devastating pest of the sweetpotato [Ipomoea batatas (L.) Lam.] worldwide. Attempts to develop host-plant resistance have been only moderately successful due in part to deficiencies in parent and progeny selection methods. Host-plant phytochemicals play critical roles in insect behavior, modulating a cross-section of key behavioral decisions. Thus, identification of the phytochemicals the female weevil uses in decision making could greatly facilitate development of host-plant resistance. The volatile chemistry of the sweetpotato was studied in relation to the host-finding behavior of the female weevil. Critical biologically active volatiles were determined via isolation (Tenax trapping), fractionation (gas chromatography-thermal conductivity detector), identification (gas chromatography and gas chromatography-mass spectroscopy), and bioassay (olfactometry). Differences in volatile chemistry among sweetpotato clones that may relate to differences in resistance or susceptibility to the female SPW were assessed. Volatile extracts from storage roots (site of oviposition) and aerial plant parts were attractive to female SPW, the former being substantially greater. In total, 33 compounds were identified from storage roots and aerial plant parts, including 23 terpenes. Three oxygenated monoterpenes (nerol, Z-citral, and methyl geranate), found in storage roots but not aerial plant parts, were identified as attractants. The sesquiterpene volatile fraction was repellent to female SPW with α-gurjunene, α-humulene, and ylangene active in the concentration range emanating from storage roots. The aerial plant parts emanated a higher composite concentration of sesquiterpenes than storage roots. Differences in the relative attraction among four sweetpotato cultivars to female SPW was inversely correlated with the composite concentration of headspace sesquiterpenes. Selection of clones with decreased volatile attractants and/or increased deterrents using an analytical means of quantification may significantly facilitate developing resistance to the SPW.