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Jonathan R. Schultheis and Dennis E. Adams

Boron has been used to overcome the disorder blister in varieties such as `Jewel'. `Hernandez' is an attractive, good-yielding variety with uniform shape that will consistently pack out at 80% to 90%. Over time in storage, however, roots develop blister-like symptoms, rendering roots unmarketable for fresh market. Our objective was to evaluate the effect of different B rates and application times on the yield and quality of `Hernandez' roots. Rates were varied up to 2.24 kg actual B/ha 6 days after planting, while various soil and foliar application times (6, 34, and 69 days after planting) were evaluated at 1.12 kg·ha–1. In 1994, three row plots were arranged in a randomized complete block design and replicated four times. Planting was on a deep sand to maximize the effect of the B carrier Solubor. Roots were harvested, graded, and weighed 120 days after planting and storage roots evaluated for blister-like symptoms in Mar. 1995. No significant differences in yield were attributed to B rate or application method. Blister-like symptoms were more severe when no B was applied; however, application of B did not eliminate symptoms, as most roots had the blister-like appearance. Boron application did not solve the problem, but symptoms were less apparent when some B was applied.

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A.Q. Villordon, J.W. Franklin, and W. McLemore

This report summarizes the results of irrigation studies conducted from 2000 to 2005 at the Sweet Potato Research Station, Chase, La. These studies investigated the role of various scheduling methods, soil moisture measurement devices, and irrigation delivery methods in sweetpotato production. The studies indicate that 15 to 20 inches of total rainfall and supplemental irrigation is required to produce 400 to 525 bu/acre of US#1 storage roots in Beauregard. Supplemental irrigation can be scheduled based on this benchmark, potentially reducing over-irrigation during dry periods. We have also found that during dry periods, irrigating every furrow can bring about 50% difference in US#1 yield vs. supplying irrigation to alternate furrows. During growing seasons characterized by optimum rainfall patterns, we did not detect any response in US#1 yield to various irrigation treatments. We evaluated several moisture measurement devices including granular matrix sensors, evaporation pan, time domain reflectometry (TDR)-based instrument, and tensiometers. We found the TDR-based device easy to use and convenient in terms of its portability. Based on studies conducted in 2001 and 2002, this device demonstrated potential as a management tool in sweetpotato production. For instance, a management allowable deficit (MAD) of 25% available moisture as measured using the TDR-based device can potentially result in the same yield as weekly irrigation and a MAD of 50% available moisture. When used properly, irrigation scheduling can reduce over-irrigation and contribute to overall efficiency in the use of production inputs.

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Melvin R. Hall

`Red Jewel' sweetpotato [Ipomoea batatas (L.) Lam.] roots were cured [32 ± 1C, 85% relative humidity (RH)] for 7 days immediately after harvest and then subjected to selected single or combined applications of additional curing, midstorage heating, and presprouting not to exceed 21 days. Extended curing was applied for 0, 7, 14, or 21 additional days before storage (16 ± 1C, 85% RH). Midway through storage, roots were heated (32 ± 1C, 85% RH) for 0, 7, 14, or 21 days and placed back into storage. Before being bedded, roots were presprouted (32 ± 1C, 85% RH) for 0, 7, 14, or 21 days. Roots that received extended curing, midstorage heating, or presprouting or a combination of these treatments emerged earlier and produced more cumulative early, midseason, and total plants than nonheated roots. Roots heated once for 21 days produced more plants than roots heated once for 14 days; those heated for 21 days in a combination of short durations produced more early, midseason, and total number of plants than roots heated once for 21 days.

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W.J. McLaurin and S.J. Kays

Four high-yielding sweetpotato [Ipomoea batatas (L.) Lam.] cultivars displayed substantial leaf shedding, under typical field production conditions, that was not due to pathological or herbivory causes. Losses ranged from ≈ 45% to 60% of the total leaves formed by the normal harvest date during 2 years. There was a strong positive correlation between leaf shedding and the number of vines (r2 = 0.80) and nodes (r2 = 0.89) per plant. Likewise, positive correlations were found between leaf shedding and total dry weight (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. `Jewel' allocated a lower percentage of dry matter into vines and a higher percentage into storage roots. Estimated leaf dry matter losses due to leaf shedding ranged from 1.2 to 2.6 t·ha-1. High leaf losses appear to be closely related to vigorous vine growth and subsequent shading of older leaves but did not have a negative impact on storage root yield in the cultivars tested.

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S. Burrell, D. Mortley, P. Loretan, A.A Trotman, P. P David, and G. W. Carver

The effects of light intensity on three sweetpotato cultivars [Ipomoea batatas (L.) Lam] were evaluated in growth chambers, as part of NASA's Closed Ecological Life Support Systems (CELSS) program for long duration space missions. Vine cuttings of `TI-155', `GA Jet', and TUJ1 were grown using nutrient film technique (NFT) in a modified half Hoagland's solution with a 1:2.4 N:K ratio in channels (0.15×0.15×1.2 m). Plants were exposed to irradiance levels of 360 or 720 umols m-2s-1 with an 18/6 photoperiod in a randomized complete block design with two replications. Temperature was set at 28:22 lightdark and RH was 70%. Differences in plant response to were more related to cultivars than the effect of light intensity. Storage root number (8) fresh, (786 g/plant) and dry weights (139 g/plant) were highest for `TI-155' while foliage fresh and dry weights were highest for `TUJ1' when averaged across light levels. TI-155' (921 g/plant) and `GA Jet' (538 g/plant) produced greater yields at higher irradiance. `TUJ1' produced a higher yield (438 g/plant at the lower intensity compared to 219 (g/plant) at the higher intensity, suggesting this cultivar could produce storage roots in similar conditions in a CELSS.

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Desmond G. Mortley

Greenhouse studies were conducted to evaluate 5 levels of Mn (0.00025 to 0.1 g.L-1) on Mn toxicity or tolerance of sweetpotato [Ipomoea batatas (L.) Lam] grown in a modified half Hoagland's solution. The presence of oxidized Mn on the roots and leaves was demonstrated by the blue staining test with benzidene and the solubility and bleaching of oxidized Mn in the oxalic-sulfuric acid solution. Both storage root and foliage fresh and dry weights were highest at Mn concn of 0.00025 g.L-1 in the nutrient solution, while fibrous root dry weight was highest with 0.01 g.L-1 Mn in the solution. More Mn accumulated in foliage than in fibrous roots for all levels of Mn evaluated. N, P, and K concn in foliage was highest at a Mn concn of 0.1 g.L-1 Mn in the solution. Foliage dry weight was preserved up to a high Mn level of about 2700 ug. g-1 Mn in tissues, while taht for storage roots was preserved up to a high Mn level of about 1000 ug. g-1 in the tissues. Deposition of oxidized Mn was observed on fibrous roots particularly at the highest Mn levels in the nutrient solution.

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Howard F. Harrison, Joseph K. Peterson, and Maurice E. Snook

Bioasssay-guided investigation of constituents possibly contributing to the allelopathic potential of sweetpotato led to the isolation of a nonpolar seed germination inhibitor in sweetpotato (Ipomoea batatas L.) roots. Mass spectral data supported by HPLC s pectroscopic analyses and data obtained from hydrolysis products revealed the presence of three monogalactosyl-diglycerides (MGDGs) (galactosyl-di-linoleneoyl glyceride, galactosyl-linoleneoyl-linoleoyl glyceride, and galactosyl-di-linoleoyl glyceride) in storage roots. The compounds inhibited proso millet germination, and at 100 ppm inhibition was about 90%. MGDG with fully saturated fatty acids (galactosyl-distearoyl glyceride) was not inhibitory in the bioassay. An efficient method for quantitation of individual MGDGs was developed, and the contents of each compound in the storage root tissues of 12 genetically diverse cultivars and breeding lines were determined. On a dry weight basis, total MGDG contents ranged between 107 and 452 μg/g in the periderm, 298 and 807 μg/g in the cortex, and 296 and 755 μg/g in the stele. Also, large differences in the ratios of the three compounds between clones and between tissues within a clone were noted. The differences between clones indicate that manipulating total content and ratios of MGDGs through plant breeding is feasible.

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D.G. Mortley, P A. Loretan, A.A Trotman, P. P David, L.C Garner, and G. W. Carver

The effects of altering, nutrient solution N:K ratio on growth of `TI-155' sweetpotato [Ipomoea batatas (L.) Lam] was evaluated in a greenhouse, as part of NASA's Closed Ecological Life Support Systems (CELSS) program for long duration space missions. Vine cuttings of `TI-155', were grown using nutrient film technique (NFT) in a modified half Hoagland's solution in channels (0.15×0.15×1.2 m). Plants were grown for 42 days in a culture solution in which N was doubled (6 mM) in order to accelerate foliage growth after which treatment N:K ratios of 1:2.4, (control) 1:4.8, and 1:7.2 were initiated. A randomized complete block design with 4 replications was used. The number of storage roots/plant increased linearly as K was increased in the solution. Storage root fresh and dry weights, growth rate (g m-2 d-1), fibrous root dry weight, foliage fresh and dry weights, and edible biomass index (root mass/total plant mass), though not significant all increased as K was increased in the nutrient solution. Nutrient solution analyses showed that K uptake was greatest in plants at the highest K level, while nitrate uptake was steady over the duration of crop growth regardless of treatments.

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Heather L. Wallace, Don R. La Bonte, and Christopher A. Clark

Virus infections and genetic mutations have been implicated in the decline of sweetpotato yield and quality. Virus-tested mericlones were derived from 12 infected clones of `Beauregard' sweetpotato by meristem-tip culture. Field studies were conducted to evaluate yield differences between the virus-tested and the virus-infected plants of each respective clone. After a 90-day growing period, the storage roots were harvested, weighed, and analyzed with a colorimeter to gauge color of skin and flesh. Yield was 7% to 130% greater in virus-tested mericlones compared to their respective virus-infected clone. Data also show these 12 virus-tested mericlones vary in yield by up to 118%. This suggests genetic differences between clones greatly affect yield. The virus-tested mericlones also show a more desirable darker-red hue for skin and flesh than the virus-infected clones. The incorporation of virus-tested material into foundation seed programs could potentially increase yield and quality with little added expense to growers, thereby netting a higher return on their crop.

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

Growth chamber experiments were conducted to study the physiological and growth response of sweetpotato [Ipomoea batatas (L.) Lam.] to either 50% or 85 % relative humidity (RH). Vine cuttings of T1-155 were grown using the nutrient film technique in a randomized complete-block design with two replications. Temperature regimes of 28/22C were maintained during the light/dark periods with irradiance at canopy level of 600 μmol·m-2·s-1 and a 14/10-hour photoperiod. High RH (85%) increased the number of storage roots per plant and significantly increased storage root fresh and dry weight, but produced lower foliage fresh and dry weight than plants grown at 50% RH. Edible biomass index and linear growth rate (in grams per square meter per day) were significantly higher for plants grown at 85 % than at 50% RH. Leaf photosynthesis and stomatal conductance were higher for plants at 85 % than at 50% RH. Thus, the principal effect of high RH on sweetpotato growth was the production of higher storage root yield, edible biomass, growth rate, and increased photosynthetic and stomatal activity.