Sweet Potato Foundation Seed Survey: Yield Performance of Multiple Generations of Sweet Potato Foundation Seed in 2007 and 2008

Tara. P. Smith¹, C.Clark², and D. Ferrin².  LSU Agricultural Center:  ¹Sweet Potato Research Station, Chase, LA and ²Dept. of Plant Pathology and Crop Physiology, Baton Rouge, LA.

 Foundation sweet potato seed has been provided by the LSU AgCenter  since the mid 1930’s.  The current mission of the LSU AgCenter virus-tested foundation seed program is to produce virus-tested foundation seed stock of popular and potential commercial cultivars.  Producers supplement their on-farm seed programs with virus-tested planting stock each year.  Seed root age is designated by generation (G1, G2 and G3). G1 seed is seed that has been produced at the Sweet Potato Research Station directly from virus-tested tissue cultures. 

A foundation seed survey research trial was initiated in 2007 to examine the yield potential of several generations of foundation seed stock once it is incorporated into on-farm seed programs.  Ten producers provided two 40 lb boxes of G2-G4 seed that was evaluated in the study in 2007 and 2008.  Twenty-five and 23 treatments were included in the test in 2007 and 2008, respectively.  The seed was collected in the spring following the bedding season and subsequently bedded in seed beds at the LSU AgCenter Burden Research Center in Baton Rouge, LA. 

 In 2007, no significant differences were detected in any yield grade for U.S. No. 1, canner, jumbo or total marketable yield grade between generations.  However, G1 (generation 1) seed did produce more U.S. No. 1’s than older generations.    Similarly in 2008, no significant differences were detected in U.S. No. 1 yield grade between the different generations evaluated however the G1seed did produce more U.S. No. 1’s than did older generations. 

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Field propagation of certified sweetpotato cuttings in early spring under plasticulture

R.A. Arancibia.  Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863.

Plastic mulch and spun-bonded rowcover were evaluated to enhance growth and increase production of certified sweetpotato propagation material in early spring. Certified plant material is propagated in greenhouses during the winter and cuttings are planted in the spring for seed-stock production. Over-winter propagation in screened and heated greenhouses is expensive, so growers reduce the cost of certified material by cutting out vines from the first planting to increase the production area. Sweetpotato is a warm climate crop that requires temperature above 15.5 ^oC (60 ^oF) for growth, therefore, plasticulture was used to increase soil and air temperature early in the spring. Beauregard B-14 slips from the Mississippi sweetpotato foundation stock were planted on April 16, 2008 under a combination of black plastic mulch and spun-bonded rowcover. All plots were drip irrigated and fertilized through irrigation. Bare ground without rowcover was considered control. Treatments lasted 1.5 month when rowcover was removed (May 31). Soil and air temperatures were monitored during the trial and plant growth (root and vines) was evaluated. Sweetpotato responded favorable to plasticulture in early spring planting. Plastic mulch increased soil temperature and rowcover increased both soil and air temperatures favoring fast growth of sweetpotato roots and vines. Average daily soil and air temperatures under mulch and rowcover in the first 14 days increased 5.5^oC and 6.9^oC, respectively. Root growth in the first 6 days increased under mulch and/or rowcover. After 45 days when rowcover was removed, vine fresh weight and length under rowcover was 5 and 6 fold higher than control, respectively. In conclusion, this technology enhances field propagation of certified planting material in early spring and may reduce planting costs for sweetpotato seed-stock production.

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A Comparison of Ethephon and Conventional Vine Removal Systems for Mississippi Sweetpotato

J.L. Main, M.W. Shankle and T.F. Garrett, Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research & Extension Center, Mississippi State University, Pontotoc, MS  38863.

Sweetpotato is a perishable root crop that is exposed to mechanical damage during harvest and packaging.   Much of the mechanical damage is the removal of small amounts of epidermal layers, ‘skinning’.   Skinning is a means for numerous organisms to enter the root and cause deterioration during storage.  Skinning also allows for transpiration weight loss during storage and lowers the overall appearance and consumer acceptance of the produce.  Removal of the vines prior to harvest aids efficiency by minimizing interference with the harvest equipment.  Another benefit to vine removal is an apparent increase in maturity of the sweetpotato roots.  This is realized in the epidermal layers adhering to the sweetpotato root more tightly.

Small plot research was conducted in 2007 and 2008, along with a replicated strip plot utilizing the same treatments to evaluate mechanical and chemical methods to reduce sweetpotato skinning injury in Mississippi.  Treatments were: mechanical removal of the vine (mow), ethephon 6 lb ai/gal at 8, 16, 32, or 48 oz/a rates, and a control mow day of harvest at three application timings 1, 3, or 7 days before harvest (DBH).  Vines were mowed the day of harvest on all ethephon treatments.  In 2007, the trial was planted on May 23^rd with G2 ‘B94-14 Beauregard’ slips and treatments were applied 104 days after transplant (DAT) on September 4^th.  Harvest occurred on September 5^th, September 7^th, and September 11^th for the 1, 3, and 7 DBH treatments, respectively.  In 2008, the small plot planting date was June 20^th with G2 ‘B94-14 Beauregard’ slips and treatments were applied 101 DAT on September 29^th.  Harvest occurred on September 30^th, October 2^th, and October 6^th for the 1, 3, and 7 DBH treatments, respectively.  The 2008 strip plot trial was planted on July 1^st using G1 ‘B94-14 Beauregard’ slips and treatments were applied 105 DAT on October 14^th.  Harvest occurred on October 15^th, October 17^th, and October 21^st for the 1, 3, and 7 DBH treatments, respectively.  Ten medium sized roots from each plot were examined for skinning injuries immediately after harvest.  The number of injuries were counted for each root and then averaged for a plot mean.  Analysis was conducted using SAS software.

 In 2007, injury ratings for timing averaged across treatments ranged from 4.5 to 16.8 for 7 DBH and 1 DBH timings, respectively.  The 7 DBH timing was greater than the 3 DBH which was also greater than the 1 DBH timing.  Treatments averaged across harvest dates ranged from 8.8 to 12.4 skins per root for the 16 and 8 oz/a ethephon rates, respectively.  The 16 oz/a rate, 8.8 injuries per root, was greater than the 8 oz/a rate and the control, 12.5 and 11.6 injuries per root, respectively.  In the 2008 small plot trial the 7 DBH timing, 6.6 injuries, was greater than the 1 or 3 DBH timings with 9.2 root injuries each.  The control treatment had more skinning injuries, 12.5, than the ethephon treatments, 7.3, to 6.7, but was not greater than mowing treatment, 9.6, when averaged across treatment timing.  In the 2008 strip trial the 1 DBH timing had more injuries, 5.2, across treatments than the 3 or 7 DBH timings, 2.4 and 1.8, respectively.  Roots treated with the 48 oz/a ethephon rate had fewer injuries, 2.3, than the mowing treatment, 4.4, but was not different than the control, 3.94 injuries per root.  In all trials the longer the treatment was applied prior to harvest, either chemical or mechanical, the lower the incidence of root injury.  Although no single rate of ethephon controlled skinning injury to the same extent in each trial, the 16 oz/a rate appears to be useful for the control of skinning due to mechanical injury in Mississippi sweetpotato.

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The Use of Soil Amendments and Foliar Nutrients to Improve Sweetpotato Yield

M.W. Shankle, J.L. Main, and T.F. Garrett.  Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863.

Hydra-Hume is derived from leonardite, which is a brownish to black oxidized form of lignite coal.  The primary component of leonardite is humus, which is characterized as humic acid, fulvic acid, and humin.  Based on technical information, Hydra-Hume DG can be described as a 70% a.i. formulation of humic acid extracted from raw leonardite.  A trial was established in 2008 to evaluate the effects of Hydra-Hume DG and several nutrient products on yield of sweetpotato at the Pontotoc Ridge-Flatwoods Branch Experiment Station. Treatments were Hydra-Hume DG @ 40 and 60 lbs/a applied for 3 years, Hydra-Hume DG @  40 and 60 lbs/a applied for 2 years, Hydra-Hume DG @ 40 lbs/ac plus Kayphol 0-0-33 @ 1 and 2 qt/a at 60 DAT, Helena Acres System (Hydra-Hume @ 40 lb/a followed- by Coron 10-0-10 + 5% B @ 1 qt/a plus Ele-Max PhosCal-zinc @ 2 qt/a plus Coron FullBor 12-0-0 + 5% B @ 8 oz/a at 20 DAT, followed-by Coron 10-0-10 + 5% B @ 2 qt/a plus Coron FullBor 12-0-0 + 5% B @ 8 oz/a plus Ele-Max Phoscal LC 3-23-0 @ 8 oz/a at 35 DAT, followed-by Coron 10-0-10 + 5% B @ 1 qt/a plus Kayphol @ 2 qt/a at 55 DAT, followed-by Ele-Max PhosK-Mag LS @ 2 qt/a at 75 DAT), and an untreated with no fertilizer.  Fertilizer N, P, and K was applied according to Mississippi State University soil test results in early June both years prior to double hipping at the rate of 50-50-200 lb, respectively.  Rows were then knocked down, Hydra Hume DG treatments were applied, all plots were treated with bifenthrin at 6 oz/a, and rows were re-hipped to incorporate inputs.  Hydra Hume DG was applied using a Gandy three-point hitch fertilizer spreader.  Valor (flumioxazin) herbicide was broadcast at the rate of 0.096 lb ai/a prior to planting while Command (clomazone) was broadcast immediately after planting at 1 lb ai/a.  Beauregard B-14 was transplanted using a two-row mechanical transplanter on June 7 and 18 in 2007 and 2008, respectively.  Row spacing of the plants was 12 inches within row and 40 inches between rows.  Plots were 3 rows, 30 ft long with one untreated row between each plot.  All foliar treatments were applied with a CO₂ pressurized tractor-mounted sprayer equipped with 8002 FF nozzles, spaced 20 in apart, delivering 15 GPA.  Plots were harvested using a 1 row chain digger 103 and 117 DAT in 2007 and 2008, respectively.  Sweetpotato roots were graded according to National Sweetpotato Collaborator’s standards, counted, and weighed to determine US No. 1, canner, jumbo, and cull yield reported as number of 40 lb boxes/ac.  Total marketable yield was recorded as the sum of US No. 1, canner, and jumbo grade yields.  Analysis of Variance was conducted and means were separated using Fisher’s protected LSD (a=0.10).

 In 2007, US No. 1 grade yield was not different than the standard fertilizer program compared to any nutrient program tested.  All treatments were greater than the untreated check except for the 1^st year application of 40 lb/ac Hydra Hume alone and followed-by 1 qt/ac Kphol at 60 DAT.  However, the Helena Acres program yielded at least 30 more boxes of No. 1 grade sweetpotatoes compared to all other treatments.  In addition, Total Marketable grade yield with the Helena Acres program was greater compared to the standard fertilizer program, which was due to the accumulative effect of higher Jumbo and Canner grade yields.  In 2008, US No. 1 grade yield for all treatments was greater than the untreated check, except the 2^nd year application of 60 lb/ac Hydra Hume.  Total Marketable yield was not different for any treatment compared to the standard fertilizer program, but all treatments were greater than the untreated check.  The difference in yield between years could be a result of early verses late season rainfall in dry-land sweetpotato.  Early season rainfall (~10in) in 2007 may have advanced nutrient uptake to root set that would improve yield.  In 2008, rainfall was less than 3.5 in until August, when rainfall events accumulated more than 10 inches of rain, which would only promote root size.

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Observations of adventitious root initiation and storage root formation under field conditions

Arthur Villordon¹, Don LaBonte², and Julio Solis²

¹LSU AgCenter Sweet Potato Research Station, Chase, LA 71324; ²LSU AgCenter School of Plant, Environmental, and Soil Sciences, 137 J.C. Miller Hall, Baton Rouge, LA 70803.

Destructive sampling of plants was conducted starting at 3 days after transplanting (DAT) to observe the initiation of adventitious roots and the onset of secondary meristematic activity in the root stelar region. Under conditions of optimal soil moisture (50% of field capacity), initiation of adventitious roots were observed as early as 3 DAT. Under similar moisture conditions, secondary meristematic activity was observed as early as 13 DAT. Visible pigmented storage roots, defined as more than 0.5 cm at its widest section, were observed as early as 26 DAT. For some plots, soil moisture stress 20 DAT was simulated using a plastic canopy. The plastic canopy was removed 20 DAT and normal irrigation was resumed.  Storage root formation was highly variable at 60 DAT from plots with simulated moisture stress. The implications of these observations for optimizing management inputs like transplant quality, irrigation, and nitrogen fertilization will be discussed. 

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Modeling and inference using a Bayesian belief network learned from empirical yield data

Arthur Villordon

LSU AgCenter Sweet Potato Research Station

Chase, LA 71324

Yield data from 2007 and 2008 were used for structural learning of candidate Bayesian belief networks (BBN) for US#1 yield. The following variables were used: growing degree days, air temperature (mean maximum and minimum), soil temperature (mean maximum and minimum), and mean solar radiation. Agroclimatic variables were measured in 10-day intervals within 30 days after transplanting. Several BN algorithms were used. A BN network that correctly classified 73% of instances in stratified cross validation will be used for demonstration of modeling and inference. This BN was learned using agroclimatic data from 10 to 20 DAT with the tree augmented naïve Bayesian classifier as implemented in Weka v. 3.5.8. Advantages and disadvantages of the Bayesian network approach will be outlined. The potential use of BNs for decision support, quantitative risk assessment, and for further understanding the sweetpotato production system will be demonstrated.

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Using GIS/GPS techniques to evaluate soil insect and/or nematode pest control strategies in sweet potato

 Eugene Burris, D. Burns, T. Smith, C. Overstreet and M. C. Wolcott
LSU AgCenter, Northeast Research Station, Chase Sweet Potato Station and Department of Plant Pathology and Crop Physiology, Louisiana State University, Louisiana State University Agricultural Center, Baton Rouge Louisiana

Recently, LSU Ag Center Research and Extension personnel have attempted to characterize sources of variability within loess soils by using tools such as the Veris® cart for measuring apparent electrical conductivity (EC_a) which is a good substitute for soil texture as well as depth to the hardpan, Real Time Kinetic Geographical Position Systems (RTK GPS), and normalized vegetative index (NDVI).  These GIS/GPS tools were used to evaluate the potential for using lime and fertilize treatments applied “as needed” for correction of soil Ph and nutrient deficiencies and for site-specific application of .fumigation treatments.  An observation on the early movement of cucumber beetles was evaluated at one location.  There is limited research of this type for Louisiana sweet potato production.  However, these studies suggest use of GIS/GPS techniques has the potential to help sweet potato producers fine tune lime and fertilize treatments and also provide relief from costly blanket applications of nematicide treatments; both major expenses incurred in sweet potato production.  Zone management strategies similar to the methods used in studies conducted in the delta since 2001 were modified for use as sample plans on the Macon Ridge.  The Veris® cart provides a method of separating fields into low – high silt and clay content. The Veris® EC_a has a very high positive correlation to clay content.  Three EC_a zones were typically used because of the narrow range of electrical conductivity measured in the loess soil regions.  One acre grids were also utilized in the sample plans.  Grids overlaid on GIS maps served to organize placement of the GPS sample points. Therefore, the final soil sampling procedure was derived from a combination of scientific and subjective techniques.

EVALUATION OF CROP ROTATIONS AND NEMATICIDES FOR MANAGEMENT OF RENIFORM NEMATODE IN SWEETPOTATO

T. P. Smith¹, A.Hammond², R. Story² and E. Burris³.  LSU Agricultural Center:  ¹Sweet Potato Research Station, Chase, LA and ²Dept. of Entomology, Baton Rouge, LA and ³Northeast Research Station, St. Joseph, LA.

Reniform nematode, (Rotylenchulus reniformis Linford and Oliveira) is a serious pest of sweetpotato in Louisiana.  Reniform nematode is present to some degree in most sweetpotato production fields.  Damage from this nematode is difficult to recognize and in most cases no distinct foliar symptoms can be detected.  The nematode will result in underdevelopment of roots and in root cracking when high populations are present.  The threshold for this pest in Louisiana is 1,000 per pint of soil.  At present, no commercially available sweetpotato varieties express resistance to this nematode.   Producers currently rely on crop rotation schemes and various chemical nematicides to manage this pest in commercial fields. 

 A crop rotation study was initiated in 2005, to evaluate the effect of several agronomic crop rotations on reniform nematode populations.  The study was designed as a randomized block design and plot size was 4 rows by 100 feet.  The crops evaluated included: sweetpotato, cotton, grain sorghum, wheat, soybean, corn and fallow ground.  Each of the crops was planted for 2 consecutive years followed by 2 years of sweetpotato in all plots.  Nematode samples were collected in the fall of each year, following harvest. 

 A separate study was initiated in 2007 to evaluate the efficacy of several labeled nematicides (Temik 15G®, Telone II®, KPAM® and Pic-chlor 60®) in sweetpotato, in a reniform nematode infested sweetpotato field.  The study was arranged in a randomized block design and plot size was 4 rows * 60 feet.  Sweetpotatoes (Beauregard 2007, Evangeline 2008) were planted on 12 inch centers and were harvested approximately 110 days after transplanting.  All nematicides were applied according to label directions.  Yield data and nematode samples were collected at harvest. 

Cumulative analyses for all years, indicated that non-host crops for reniform nematode (grain sorghum, corn and fallow ground) resulted in the lowest populations of this pest in the crop rotation study.  All nematicides evaluated resulted in increased yields compared to non-treated control plots and Telone II® evaluated at a 6-gallon rate resulted in the highest yields of all treatments in 2007 and 2008. 

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Effect of KIH-485 on Weed Control and Sweetpotato Yield

M.W. Shankle, T.F. Garrett, and J.L. Main.  Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research & Extension Center, Mississippi State University, Pontotoc, MS 38863.

Currently, sweetpotatoes have the highest per acre dollar return of any vegetable crop in Mississippi.  With this high dollar per acre return weed control is an import part of maximizing yield and profits.  Command (clomazone) applied at transplant has been the major option for grass control in sweetpotatoes for most producers.  While Command provides good grass control it does not provide adequate control of many broadleaf weed species.  Since receiving a label for its use in sweetpotato, Valor (flumioxazin) has provided this needed broadleaf weed control.  However, Valor must be applied pre-transplant and most growers prefer a post-transplant application due to time-limited land-prep operations.  KIH-485 is a new herbicide that is being developed by Kumiai Chemical Co.   KIH-485’s mode of action is likely that of a seedling growth inhibitor similar to metolachlor. Early indications have shown it being an effective chemical for preemergence grass control and for the control of several broadleaf weed species.  KIH-485 controls many important annual grass weeds in the  Setaria, Digitaria, Echinochloa, Panicum, and Sorghum genera and some sedges.  KIH-485 also controls many broadleaf weeds including species in the Amaranthus, Datura, Kochia, and Polygonum genera.  The goal of this trial was to determine if KIH-485 has acceptable crop tolerance, grass control, and broadleaf weed control for use in sweetpotato.

A trial was conducted at the Pontotoc Ridge-Flatwoods Branch Experiment Station in Pontotoc County, Mississippi on a Falkner silt loam (Fine-silty, siliceous, thermic Aquic Paleudalfs) in 2008. The trial area was prepared by disk cultivation, do-all, and bedding.  Granular fertilizer was applied broadcast according to soil test recommendations prior to planting.  Field grown ‘Beauregard B-14’ slips were transplanted using a mechanical transplanter on July 3^rd.  The experimental design was a randomized complete block design with 4 replications.  Plots were three rows spaced 40 inches apart and plants were spaced 12 inches apart within the row. Treatments of were applied with a CO₂  pressurized sprayer with 8002 flat fan nozzles spaced 20-in apart with a spray volume of 15 GPA.  Treatments include KIH-485 at 1.5, 2.0, 2.5, and 3.0 oz/A applied post-transplant and flumioxazin at 2.5 oz/A applied pre-transplant + clomazone at 2.66 pt/A applied post-transplant.  Visual observations of crop injury and weed control were made at 4, 7, 21, and 28 days after transplant (DAT).  Sweetpotato roots were harvested using a one-row mechanized chain digger on October 13^th for a total of 102 growing days.  Roots were graded into US No. 1, Canner, Cull, and Jumbo grade yields using the National Sweetpotato Collaborator’s standards and reported as number of 40 lb boxes/A.  Analysis of variance was conducted on weed control and yield using Fisher’s protected LSD (α=0.05).

 AT 4 DAT, sweetpotato injury was observed at 5% for all KIH-485 treatments, with no injury observed for the Valor + Command treatment.   No other injury was observed after 4 DAT.  Pigweed control was at least 90% for all treatments at 21 DAT.  AT 28 DAT, all KIH-485 treatments controlled pigweed at least 90%, which was higher than the treatment of Valor + Command.  Grass control was at least 90% at 7 DAT for all treatments except KIH-485 at 1.5 oz/A, which had a control of 83%.  At 28 DAT, grass control ranged from 73 to 90% for KIH-485 at 1.5 oz/A and Valor + Command, respectively.  With increased rates of KIH-485 improved grass control was observed.

US No. 1 yield ranged from 5 to 288 boxes/A for the untreated and Valor + Command, respectively.  Total marketable yield ranged from 23 to 441 boxes/A for the untreated and Valor + Command, respectively.  The highest yielding treatment of KIH-485 was the 3oz rate, which yielded 273 and 390 boxes/A for US No. 1 and Total marketable, respectively.  This yield was comparable to the treatment of Valor + Command.

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DEVELOPING MANAGEMENT STRATEGIES FOR AN INVASIVE WHITE GRUB PEST OF SWEETPOTATO IN NORTH CAROLINA. 

M.R. Abney, Dept. of Entomology: North Carolina State University, Raleigh, NC.

Plectris aliena is an exotic white grub species that has caused significant economic loss to sweetpotato (estimated by growers to exceed $3 million) in North Carolina in the past three years. The rise in the importance of P. aliena in North Carolina sweetpotato is unexplained, and the potential of this pest to expand its range into other important production areas is unknown. There are currently no effective tools for managing this insect, and it poses a considerable threat to the sweetpotato industry. Only limited research has been conducted on this insect, and this project focused on providing relevant biological information that could be used to develop control strategies. Results of preliminary biological studies indicate that P. aliena has a one year life cycle in NC. Adult mating flights were observed in 2008 from late May until late June. The beetle overwinters in the soil as a late instar grub at depths of up to 11 inches. Laboratory bioassays resulted in low mortality of both early and late instar grubs exposed to selected insecticides. Experiments in 2007 and 2008 evaluated the effect of insecticides on grubs in commercial sweetpotato fields. None of the materials tested provided acceptable levels of control in 2007. On-going research is aimed at developing integrated control strategies for P. aliena in sweetpotato.

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Effects of Meristem Culture on Yields of Heirloom Sweetpotatoes in the Field

 D. Michael Jackson, Kai-Shu Ling, and H. F. Harrison, Jr.

 U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC 29414

During 2005-2007, 23 heirloom sweetpotato varieties were taken through meristem shoot‑tip culture to generate virus-free plants.  These cultivars were then grown in 12-plant plots that were replicated four times at the U.S. Vegetable Laboratory during the summer of 2008.  These plots included the cleaned-up material  (“clean”) that had been taken through meristem culture and PCR-tested and the original plant introductions (“dirty”) that had been re-infected with sweet potato leaf curl virus (SPLCV) through whitefly transmission by Bemisia tabaci (Gennadius) inside a greenhouse.  Normal production practices were followed except that no insecticides were applied to these plots.  Overall, there were highly significant differences in the weight of the clean vs dirty plots.  All of the varieties had numerically higher yields in the clean plots, and for 12 varieties these differences were statistically significant.  The clean plots ranged 1.1-7.4 times more yield than the dirty plots.  There were also significantly more roots in the clean plots of most of the heirloom varieties.  PCR analysis of storage roots and leaf material confirmed that the yield increases were related to the elimination of viruses from these materials.

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Determination of anthocyanin content in purple-fleshed sweetpotatoes

V. D. Truong¹, Z. Hu¹, R. L. Thompson¹, K. V. Pecota² and G. C. Yencho² 

¹USDA-ARS, SAA Food Science Research Unit, ²Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695

Purple-fleshed sweetpotatoes can be a healthy food choice for consumers and a potential source for natural food colorants. Analysis of anthocyanins responsible for the purple flesh color is important for breeding programs and the development of value added processed products. The objective was to evaluate the current analytical methods for quantifying the anthocyanin content in purple-fleshed sweetpotatoes.  Freeze-dried powders of purple-fleshed sweetpotato clones were extracted with acidified methanol using a Dionex ASE 200 accelerated solvent extractor. Optimal conditions for anthocyanin extraction were determined by response surface methodology. Anthocyanin content of the extract was characterized by a) absorbance measurement at 530 nm (A₅₃₀), b) color value protocol, and c) a pH-differential method. Results indicated that the highest anthocyanin yields were at 60-80% acidified methanol and 80-120ºC. Among 682 samples analyzed, the anthocyanin content varied widely from < 1mg to 662 mg cyanidine-3-glucoside equivalent/100g powder with a majority in a range of 25-250 mg/100g powder. The total anthocyanin contents determined by the pH-differential method were highly correlated with the absorbance at 530 nm (R² = 0.79) and color values (R² = 0.91). A predictive equation describing the relationship between the anthocyanin content and the Hunter color values (L*, a*, b*) of the freeze-dried sweetpotato powders was developed. These results can be helpful in comparing the anthocyanin contents assayed with these methods that are reported by various sweetpotato breeding programs.

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Sweetpotato storage trials:  variety differences, storage conditions, and fertilizer effects.

C. S. Stoddard* and Mikal Saltveit¹

*UC Cooperative Extension, Merced, CA; ¹Department of Plant Sciences, UC Davis

 In recent years, food processors have become buyers of California sweetpotatoes (Ipomoea batatas) to produce sweetpotato fries.  Experience has shown that by February, raw product quality deteriorates as a result of sugar accumulation, increased fiber, and general breakdown that occur during long-term storage conditions typical for the area.  Sugar accumulation in storage is problematic for processing because it creates darker colors and changes in texture, both undesirable in the finished product.  Therefore, a multi-tiered project was conducted to observe the effect of varieties, in-season N and K management, and storage conditions (temperature, relative humidity, and CO₂) on storage loss and sugar levels in orange-flesh sweetpotatoes.  Significant differences were found between the varieties tested in their cumulative long-term (180 days) weight loss in storage.  Covington and Beauregard had the least amount of loss, at 8.2 and 8.4%, whereas Evangeline and Diane were highest, at 13 and 13.5%.  Nitrogen and potassium fertilizer source did not significantly affect yield or long-term storage weight loss, but early applications of nitrogen tended to improve yields and significantly (p ≤ 0.1) reduced cumulative weight loss after February as compared to applying nitrogen throughout the season.  Long-term weight loss in controlled storage conditions was least (6%) when Beauregard roots were stored at 90% relative humidity; combining slight chilling stress (54° F) and low relative humidity (70%) produced significantly more weight loss than either alone (12%).  Elevated CO₂ (3%) reduced weight loss and glucose accumulation in roots stored at 54° F.  The results from the first year of this study suggest that improvements can be made in long-term root storage quality through variety selection, fertilizer management, and increased relative humidity in storage.  Preliminary results from 2008 will also be presented.

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