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D. G. Mortley, C. K. Bonsi, W. A. Hill, P. A. Loretan, C. E. Morris, A. A. Trotman, and P. P. David

Growth chamber studies were conducted to determine growth responses of sweetpotato [Ipomoea batatas (L.) Lam) to differing photoperiods (PP) when grown by use of NFT. Four vine cuttings (15 cm length) of GA Jet and TI-155 were grown for 120 days at 12/12, 15/9, 18/6, and 21/3 light/dark PP. Irradiance averaged 427 umol m-2 s-1, with day/night temperatures of 28/22C and 70% RH. A modified half Hoagland's solution was used. Number of storage roots/plant, and storage root fresh and dry weights for GA Jet increased as PP increased from 12 to 21 h, while storage root fresh and dry weights for TI-155 increased up to 18 h PP but declined at 21 h PP. Storage root number/plant for TI-155 declined at 15 h PP but was higher at both 18 and 21 h PP. Highest foliage dry weight for GA Jet was obtained at 21 h PP while that for TI-155 was obtained at 18 h PP. Leaf area index (LAI) for GA Jet increased with increased PP, while LAI for TI-155 increased with increased PP up to 18 h then declined at 21 h PP.

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Petra J. Wolters and Wanda W. Collins

Streptomyces soil rot or pox, caused by the actinomycete Streptomyces ipomoea, is a destructive root disease of sweetpotato. Evaluation for resistance to S. ipomoea in naturally infested fields, requires much space and results may vary from year to year. In this study a greenhouse method for evaluating the response of sweetpotato clones to infection with S. ipomoea was developed. The greenhouse method used fibrous roots, developed on terminal vine cuttings. Experiments showed no time by clone interaction, indicating that this method gave consistent results when repeated. A study to determine corrrelation between field resistance of clones and resistance as found by the greenhouse method was done. Thirty-nine clones were screened for resistance using the greenhouse method and were also planted in a field naturally infested with S. ipomoea. Severity of disease on fibrous roots (greenhouse method) and on storage roots (field method) was evaluated visually using a scale of 0 to 5 (0: no symptoms. 5: severe symptoms). Although correlations between data from the greenhouse and field methods were low lo moderate (r=0.17 to 0.49). extremely susceptible or resistant clones were identified as such by both methods. These results suggest that it is possible to select clones with high resistance to S. ipomoea using the greenhouse method, which provides a better controlled environment, and requires less space than field evaluations.

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Dapeng Zhang, Wanda W. Collins, and Maria Andrade

Sweetpotato [Ipomoea batatas (L.) Lam.] is intensively used as an animal feed in many developing countries. Information about trypsin inhibitor activity (TIA), an antinutritional component in this crop, will be useful for breeding sweetpotato as animal feed. Nine sweetpotato lines were grown at two locations and fertilized or nonfertilized conditions at each location. Samples were analyzed for TIA using a substrate-specific colorimetric method. Soybean [Glycine max (L.) Merr.] seeds were used to compare the levels of TIA in sweetpotato and soybean. Activity in roots ranged from 29.5 to 55.0 units in the nine lines. The mean TIA in roots was 40.7 units averaged over lines and environments, which was ≈28% of the mean for the five soybean cultivars. Activity in sweetpotato vines was only ≈14.6% of that in the roots, and TIA in fertilized plots was 150% and 67% higher than that in nonfertilized plots in the two locations, respectively. There was a small but significant positive correlation between TIA and crude protein in roots. These results suggested that TIA in sweetpotato storage roots may be high enough to have a substantial nutritional impact on animals, whereas TIA in vines is very low and should be of less nutritional concern.

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W.J. McLaurin and S.J. Kays

Under typical field production conditions, four high-yielding sweetpotato cultivars (Centennial, Jewel, Regal and Resisto) were found to lose substantial amounts of leaves due to natural senescense rather than pathological or herbivory causes. Leaf loss by the normal harvest date ranged from 46 to 63% of the total leaves formed in 1991 and 48 to 59% in 1992. There was a strong positive correlation between leaves lost and the number of vines (r2 = 0.80) and nodes (r2 = 0.89) per plant. Positive correlations were also found between leaf loss and total dry weight of the plant (r2 = 0.67). root fresh weight (r2 = 0.65). root dry weight (r2 = 0.60), and vine dry weight (r2 = 0.68). Distinct differences were found among cultivars in dry matter allocation within the plant. Of the cultivars tested, 'Jewel' allotted a lower percentage of dry matter into vines and a greater percentage into storage roots. Estimated leaf dry matter losses due to leaf shedding ranged from 1.2 to 2.6 MT·ha-1. Amount of leaf loss appeared to be closely related to vigorous vine growth and subsequent shading of older leaves, though leaf loss did not have a negative impact on storage root yield in the cultivars tested.

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Stanley J. Kays, Jyh-Bin Sun, and Ray F. Severson

Changes in the concentration of individual sugars in sweetpotato storage roots with cooking and their relationship to the formation of volatile compounds were studied. During cooking maltose concentration increased from 0.03% fwt at 25.C to a maximum of 4.33% at WC. Microwave pretreatment (2-4 minutes) resulted in a significant decrease in amounts of maltose and volatiles formed. At 80°C, approximately 80% of maltose synthesis was inhibited when pretreated with microwaves. Adding maltose into microwave pretreated samples and then cooking in a convection oven restored most of the volatile profile with the exception of phenylacetaldehyde. Upon heating (200°C), sweetpotato root material that was insoluble in both methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the non-polar methylenc chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. It was concluded that maltose represents a primary precursor for many of the volatile compounds emanating from baked `Jewel' sweetpotatoes and the formation of these volatiles appears to involve both enzymatic and thermal reactions.

Open access

J. M. White and J. O. Strandberg

Abstract

Early root growth of carrots (Daucus carota L.) was studied in specially constructed pots containing organic soil under controlled environments at 16°, 20°, 24°, and 28°C. Carrot tops produced greater amounts of bio-mass on a fresh or dry weight basis than did roots, whereas taproots demonstrated faster rates of linear growth than did the tops throughout the 24-day sampling period at all temperatures. The optimum range of temperatures for carrot root growth was 20-24°C. Taproots reached the potential length for market-acceptable storage roots (15.2 cm) between 12 and 16 days after planting at 20°, 24°, and 28°C and after 20 days at 16°C. Average taproot lengths after 24 days at 16°, 20°, 24°, and 28°C were 23.6, 38.5, 35.6, and 16.7 cm, respectively. Secondary roots had developed by the 8th day and tertiary roots by the 20th day. Tertiary roots were confined to the upper 5 cm of the root system at this early date.

Open access

D. W. Walker and D. D. Jenkins

Abstract

Possible allelopathic effects of decaying sweet potato plant residue on sweet potato [Ipomoea batatas (L.) Lam.] and cowpea [Vigna unquiculata (L.) Walp.] growth were assessed. Residue treatments consisted of factorial combinations of 2 sweet potato cultivars (‘Jewel’ or ‘Centennial’), 2 plant parts (vines or storage roots), and 2 methods of tissue preparation–dried, or frozen and then dried. Ground sweet potato residues were mixed with sand [2.7% residue (w/w)] and placed in pots. Dry weights of ‘Jewel’ sweet potato plant shoots 57 days after planting were reduced 32% and 74% by vine and storage root residues, respectively, while dry weights of ‘Centennial’ sweet potato plant shoots were reduced 18% and 73%, respectively. Dried vine tissue had no apparent inhibitory effect, but vines frozen prior to drying reduced fresh and dry weights of ‘Centennial’ shoots. Dry weights of ‘Brown crowder’ cowpea plant shoots were reduced 79% and 91% by sweet potato vine and storage root residues, respectively. Nodulation of cowpeas grown in residue-amended pots was negligible compared to plants grown in pure sand. Leachate pH from pots containing sweet potato root residue was 1.4 and 2 pH units lower than that from nonamended pots with both sweet potato cultivars and cowpeas, respectively.

Open access

Melvin R. Hall

Abstract

Pot-grown ‘Georgia Jet’ sweet potato [lpomoea batatas (L.) Lam.] vine cuttings, from which the primary shoot apex was removed, developed vines with fewer secondary laterals, but more tertiary laterals, and greater lengths of both secondary and tertiary laterals than were developed when the primary shoot apex was not removed. With eight nodes exposed aboveground, cuttings without the primary shoot apex developed a greater total length of secondary laterals due to longer internodes and greater total vine length than cuttings with the primary shoot apex. Dry weights of storage roots and lateral vines were increased, but dry weight of the primary vine was reduced from cuttings without the primary shoot apex. With four nodes exposed aboveground under field conditions, cuttings without the primary shoot apex developed fewer secondary laterals, less total vine length, and less yield of jumbo grade roots than those with the shoot apex. With eight nodes exposed aboveground under field conditions, cuttings with the primary shoot apex developed a greater number and length of tertiary laterals than those without the primary shoot apex, but the primary shoot apex did not affect secondary laterals, total vine length, or storage root yield significantly.

Open access

William M. Walter Jr., Larry K. Hammett, and Francis G. Giesbrecht

Abstract

Roots of three sweet potato [Ipomoea batatas (L.) Lam] cultivars, Centennial, Jewel, and Pope, were harvested at three soil temperature ranges, cured for 1 to 7 days at 30°C and 90% to 95% RH, and stored at 13° to 13.5° and 90% and 95% RH. Wound healing during curing was evaluated using a rapid color test and histochemical methods. The color test was a good indicator of the lignification phase of wound healing for ‘Centennial’ and ‘Jewel’, and a fair indicator for ‘Pope’. Wound healing rates for the cultivars were similar. Roots harvested from the warmest soils (22° to 25°) had higher color scores (most wound lignification) up to 3 days of curing. After 5 days, there were ≈2.7 layers of lignified cells and one layer of wound periderm. After 16 weeks of storage, roots harvested at soil temperatures of 10° to 12° and 22° to 25° had lost more weight and developed more rots than did roots harvested at 15° to 17°, despite the fact that wound healing progress was similar. Thus, factors other than wound healing strongly influence storage stability.

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Jaejoon Kim and David J. Wolyn

bags, at 5 °C, until sampling. The portion of the crown, where new buds were visible, was selected. Crowns were separated into storage roots and rhizomes. Storage roots were harvested near the rhizome in segments of ≈5 cm, weighed, and placed in a