Production, Physiology, and Plant/Seed Production

“Sweetpotato Color Analyses”
D. Michael Jackson*^1
1USDA-ARS, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC 29414.

Color is an important attribute that contributes to the appearance of a sweetpotato genotype. A consumer uses color, along with geometric attributes (e.g., gloss, luster, sheen, texture, opaqueness, shape), to subjectively evaluate the appearance of a sweetpotato root. Color can be quantified by the use of a color space (color order system), which is a three-dimensional specification system with a lightness (value) and two chromatic attributes, hue and saturation (chroma). In this study, color readings were taken from several sweetpotato entries from the Sweetpotato Collaborators Trials and other advanced lines grown in replicated plots at the U. S. Vegetable Laboratory, Charleston, SC, 2007-2009. Skin and flesh colors were measured with a Konica Minolta Chroma Meter (CR-400 with 8 mm aperture and 0° viewing angle) using the CIE 1976 L*a*b* and CIE L*C*h color spaces; and data were recorded using Color Data Software CM-S100w SpectraMagic NX™ (ver. 1.7) (Konica Minolta). Within the gamut of a color space, there is an elliptical subset of colors that represents the acceptable limits for a particular flesh or skin color for a type of sweetpotato. These acceptable color space gamuts are described for several important commercial sweetpotato cultivars. This paper also looks at the year-to-year variation in color of sweetpotato genotypes.

“Temperature Effects on Sweetpotato Storage Root Growth and Development”

K. Raja Reddy¹, Bandara Gajanayake¹, Mark Shankle², Ramon Arancibia² and Arthur Villordon^3
1Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762, ²Pontotoc Ridge-Flatwoods Branch, Mississippi State University, 8320 Hwy 15 South, Pontotoc, MS 38863, ³Lousiana State University Agcenter, Sweet Potato Research Station, 130 Sweet Potato Road, Chase, LA 71324

Sweetpotato storage root initiation and growth will be affected by growth temperature, yet little specific information is available on storage root initiation and growth in response to temperature. Information covering wide range of temperatures would be useful for predicting both growth and developmental rates in sweetpotato. Therefore, two studies were conducted to determine temperature effects on sweetpotato storage root initiation and development using sunlit plant growth chambers. In experiment I,sweetpotato, cultivar ‘Beauregard’ slips were planted in pots at five day/night temperaturesof 20/12, 25/17, 30/22, 35/27 and 40/32°C for 55 days. In experiment II, four day/night temperatures of 25/17, 30/22, 35/27, and 40/32°C were imposed 16 days after planting for plants grown at optimum temperature (30/22°C) and continued for another 62 days. In both the experiments, optimum water and nutrients were provided throughout the experimental period. In experiment I, two rows of three pots row-1 were removed on a weekly basis leaving three rows with nine plants m-2 until 55 days. In Experiment II, two rows of three plants row-1were removed at 16 days leaving three rows with nine plants m-2 for the final harvest. At each harvest, root number (storage and adventitious) and dry weights of plants parts were determined. Temperature,when imposed at the beginning of planting, did not affect either total or storage roots formed. The time to reach 50% of storage root formation was significantly affected by temperature. The size and quality of the storage roots, however, were significantly affected by temperature. Total biomass produced increased up to 30/22 and 35/27°C and declined slightly at the 40/32°C. Storage root biomass increased with increase in temperature up to 30/22°C, and declined by 11 and 90% at 35/27 and 40/32°C, respectively. When temperature treatments were imposed after the storage roots are formed, the number of total and as well storage roots produced were not affected by temperature, but the size and quality of storage roots were significantly affected by temperature. The optimum temperature for total biomass production was 30/22°C and declined by 9% at 35/27°C and 27% at 40/32°C. The optimum temperature for storage root formation was 25/17 and declined linearly by 31 g 1°C increase in temperature. The functional algorithms developed from these datasets will be useful in predicting sweetpotato storage root formation.

“Interactive Effects of Temperature and Elevated Carbon Dioxide on Early-season Sweetpotato Growth and Development”

Bandara Gajanayake¹, K. Raja Reddy¹, Mark Shankle² and Ramon Arancibia^2
1Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762, ²Pontotoc Ridge-Flatwoods Branch, Mississippi State University, 8320 Hwy 15 South, Pontotoc, MS 38863

The current increase in atmospheric carbon dioxide concentration [CO2] and projected increases in global surface air temperature have stimulated the need for understanding the response of agricultural crops to [CO2] and temperature interactions. The objectives of this study were to evaluate the effects of temperature and [CO2] interactions on sweetpotato growth and development. Sweetpotato (cv. ‘Beauregard’) was grown day/night temperature cycles of 20/12, 25/17, 30/22, 35/27, and 40/32°C and [CO2] treatments of 380 and 760 µL L-1at each temperature for 55 days with optimum water and nutrients. The slips were planted in pots in 11 rows of 3 pots per row-1 with pure, fine sand as rooting medium. Six pots were removed on a weekly basis leaving three rows with nine plants m-2 until 55 days. At each harvest, vine length, leaf and root numbers (storage and adventitious), leaf area, and dry weights of various plant parts were determined. Temperature and [CO2] had significant effects on vine length and leaf number. Vine length increased linearly from 20/12 to 35/27°C and declined slightly at the 40/32°C. Elevated [CO2] did not affect vine growth at any temperature. Total leaf number, on the other hand, increased linearly with increase in temperature. Elevated [CO2], on average, produced 18% more leaf area due more number of leaves producedplant-1. Total biomass produced showed quadratic and bi-linear response to temperature at ambient and elevated [CO2], respectively; increased up to 35/27°C and declined at 40/32°C. Temperature for optimum total biomass production was 29°C for plants grown in ambient [CO2]. Elevated [CO2] shifted the temperature optimum by 3°C. Storage root growth showed similar trends with that of total biomass production. However, the storage root growth was severely reduced at the highest temperature, 40/32°C. Even though the temperature optimum shifted for storage root mass similar to total biomass production, elevated [CO2] did not have any effect on storage root biomass production across the temperature tested. The temperature optimum for storage root growth was lower than the total biomass production. Cultivars that produce more storage root mass at high temperature would be more productive both in the present-day sweetpotato producing environments and in the future warmer climate.

“The Effect of Salty Water Irrigation on Sweetpotato Storage Root Formation”
Nurit Firon¹, Zion Shemer², Yanir Kfir¹, Michal Amichai², Etan Pressman¹ and Levia Althan^1
1 Inst. of Plant Sciences, The Volcani Center, ARO, P.O. Box 6, Bet Dagan, 50250, Israel.
² Ramat Negev Experimental Station, M. P. Haluza, 85515, Israel.

One of the challenges facing the State of Israel, which suffers from a severe water shortage, is optimal use of its available water sources. This challenge is of particular significance in the Negev, which receives most of its drinking water from remote sources outside the region. The Negev is a desert region suited for growing Sweetpotato (with two types of soil: sand and light loess, and with low average yearly rainfall of about 80 mm). Brackish water (BW) can be found in underground aquifers at a depth of 800 to 1200 meters.
In order to enable exploitation of the natural water resources in the Negev region for growing Sweetpotato, the effect of salinity (BW; EC 4.5 dS/m) on the yield of two Sweetpotato varieties (‘Georgia-Jet’ and ‘Evangeline’) was tested.
The results indicate that BW irrigation throughout the growing period (120 days) caused highly reduced yield in both tested varieties.
Previously it was found that the period spanning the first 30 days after planting was critical in determining whether adventitious roots became lignified or initiated as storage roots. Therefore, it was hypothesized that BW irrigation causes reduced yield by interfering with this initial stage of storage root development. The results indicate, however, that BW did not affect the number of storage roots formed, but rather affected the second phase of storage root development spanning 60 days after the “initiation” phase. Brackish water did not affect starch concentration, amyloplast size or parenchyma cells size, but rather the addition of new starch-accumulating parenchyma cells. The results thus point to an effect of BW on cell division, resulting in reduction in tuber growth and yield.

“Further calibration and validation of a Bayesian belief network model representing the relationship between fresh market yield and agroclimatic variables known to influence storage root initiation in ‘Beauregard’ sweetpotato: soil moisture and planting density”

A. Villordon,¹ J. Solis,² D. LaBonte,² C. Clark³, and R. Sheffield⁴

¹LSU AgCenter Sweet Potato Research Station, ²LSU AgCenter School of Plant , Environmental, and Soil Sciences.  ³LSU AgCenter Department of Plant Pathology and Crop Physiology.⁴LSU AgCenter Department of Agricultural and Biological Engineering

A uniform set of management variables was used in the development of a prototype Bayesian Belief Network (BBN) model for predicting fresh market yield in Beauregard. Further field validation is necessary to determine the structural soundness as well as the extent and limitation of model validity. In addition, further calibration is necessary in order to adjust system parameters so that simulated results approach that of actual observations. Field experiments were conducted in 2010 to verify model validity using different planting densities (variable in-row spacing, fixed row width). Due to drought conditions during most of the growing season (July-September), comparison of irrigated vs. non-irrigated plots was possible for certain planting dates. In general, the results from 2010 yield trials further validated the predictive capability of the prototype model.  The yields and times of harvest (110-120 days after transplanting, DAT) were predictable for planting dates with moderate air (≈67-90^oF) and soil temperatures (≈71-86^oF at 6 in. depth) and when soil moisture was not limiting, especially during the first 30 DAT. We have previously defined this optimum soil moisture as 25%-50% (at 6 in. depth) of field capacity for the specific soil series used in the study. With later planting dates, especially those characterized by relatively high air (>90^oF) and soil temperatures (>87^oF) and sub-optimal soil moisture, yields were less predictable and growing days were longer (>120 DAT) to enable storage root sizing.  The 2010 data further corroborated the soil moisture regimes defined in the model. Preliminary data also indicated the mitigating influence of soil moisture regime on planting density and harvest date effects on yield. Under a uniform supplemental irrigation regime, plots with simulated higher plant density (i.e., 8 in. plant spacing=18,670 plants acre^-1) either had lower yields or were harvested later relative to plots with standard plant spacing (12 in. =12,440 plants acre^-1). When soil moisture was not limiting, plots with higher planting densities had similar or relatively higher yields relative to plots with standard planting densities.

“Preliminary experience using a minirhizotron-based system for characterizing adventitious root development during the storage root initiation period: prospects and problems “

A. Villordon,¹ J. Solis,² D. LaBonte²

LSU AgCenter Sweet Potato Research Station, LSU AgCenter School of Plant , Environmental, and Soil Sciences.

Minirhizotron (MR) systems are routinely used as supplementary or stand-alone systems to study root development in other crop species. There is virtually a lack of information about the use of MRs in sweetpotatoes, especially during the critical storage root initiation period. To address this apparent knowledge gap, we performed a series of experiments to determine the optimum number and placement of sampling tubes for detecting adventitious root development in ‘Beauregard’ sweetpotato. Subsequently, we determined the ability of the MR system to discriminate between two soil moisture regimes in a simple experiment that employed rain shelters to simulate soil moisture variability in the soil profile. In general, the scanner-based MR system underestimated the actual count of adventitious roots (AR), pencil roots (PR), and storage roots (SR) regardless of the number and placement of tubes. However, two vertically positioned tubes only underestimated newly initiated ARs by 48% when sampled at 36 days after transplanting (DAT). Paired sampling tubes were subsequently used to assess the ability of MR-based system to discriminate AR development in a simple rain shelter experiment. The MR system and conventional destructive sampling detected 83% and 56% reduction in NAR count among plots with rain shelters, respectively. The current experimental approach did not permit discrimination of AR count between node locations. It was also determined that the presence of tubes interfered with SR formation of monitored AR segments. Despite this limitation, the results show the potential for incorporating MR systems in studies that aim to qualitatively and quantitatively document sweetpotato AR system response to agroclimatic variables and management interventions during the initial SR bulking stage.

“Efficacy of nematocides and metam sodium on field production of
sweetpotatoes in California” C. Scott Stoddard, UC Cooperative Extension, Merced, CA 95341

Soil fumigation, or rather the ability to use soil fumigants, remains a critical issue for the
sweetpotato industry in California. Pre-plant soil fumigation is the principle method of
pest management, as it significantly reduces losses from Root Knot Nematodes (RKN –
Moloidogyne incognita), wireworms, and grubs. Unfortunately, the availability of Telone
(1,3-D) is insufficient to meet the needs of the industry because the California
Department of Pesticide Regulation has restricted Telone use by implementing “use caps”
for the entire state. These caps limit the amount of Telone that can be used on a
township basis (one township is 36 sections; a section is 640 acres) to 92,500 lbs a.i.
Strawberries, carrots, trees & vines, roses, and sweetpotatoes are just some of the crops
that are severely impacted by these restrictions because of their geographic concentration
within certain townships in the state. In Merced County, these restrictions limit the
amount of Telone that can be used in any year to approximately 50% of demand. In
response, growers are using more metam sodium (Vapam), metam potassium (K-Pam),
and Mocap. Vapam, and its cousin K-pam are liquid soil fumigants that have shown
good control of nematodes in controlled root stock evaluation trials for orchids, but
efficacy has not been extensively tested under conditions typical for sweetpotato
production. Therefore, in 2009 and 2010, trials were conducted in commercial
sweetpotato production fields to evaluate the effect of pre-plant fumigants and
nematocides on root knot nematodes and yield of sweetpotatoes. In the fumigation trial,
Telone was applied at 6, 9, and 12 gallons per acre; metam rates were 35 and 50 gallons
per acre. All treatments were applied simultaneously using shank injections at 4” and
8” (metam) and 18” (Telone) approximately one month before transplanting. The variety
was O’Henry, a white-flesh sweetpotato very susceptible to RKN. The factorial analysis
indicated that a shank application of metam was as effective as Telone: fall RKN counts
were significantly lower in the treatments that received either fumigant, and yields were
significantly improved as compared to the untreated control. Combining Telone with
metam improved the performance of both products, and results suggest that reduced
rates of Telone can be effective when combined with metam. In 2010, various rates of an
experimental nematocide MCW-2 were compared to Telone, Mocap, metam, and
MeloCon with the nematode susceptible variety O’Henry under commercial field
conditions. All treatments except the 0.5 gpa MCW-2 treatment significantly increased
yield and decreased the amount of roots classified as culls. Yields were 15 – 42% higher
than the untreated control. While these results show that alternatives to Telone can be
very effective for sweetpotato production, regulatory restrictions on use, which include
timing and buffer zones to reduce chronic exposure, make using any alternative a
challenge for growers.

Insect, Disease, and Weed Management

“Recent Advances in the Molecular Characterization of Sweetpotato Begomoviruses”
Kai-Shu Ling*¹ and ShuoCheng Zhang^2
1 U.S. Vegetable Laboratory, United States Department of Agriculture, Agricultural Research Service, 2700 Savannah Highway, Charleston, SC 29414, ² Center for Biotechnology and Genomics, Alcorn State University, Alcorn State, MS 39096, USA.

Although sweetpotato leaf curl disease has been observed on sweetpotato in Japan and Taiwan since 1985, molecular characterization of sweetpotato begomoviruses has only been conducted in recent years. In the U.S., two begomoviruses, Sweet potato leaf curl virus (SPLCV) and Sweet potato leaf curl Georgia virus (SPLCGV) have been identified in Louisiana. Recently, several new begomoviruses were also identified on sweetpotato or morning glory (Ipomoea sp.) plants in other parts of the world, including Brazil, China, and Spain. Additionally, numerous strains or variants of SPLCV have also been identified in India, Italy, Japan, Kenya, Korea, and Peru. To determine the genetic diversity and distribution of sweetpotato begomoviruses in other sweetpotato growing regions in the U.S., we focused our efforts in molecular characterization of field collected isolates in Mississippi and South Carolina. Using rolling-circle amplification, a total of 52 clones in full-genome were obtained. Initial inspection of a sequence alignment revealed a strong genetic diversity among the U.S. isolates, tentatively grouped into 10 genotypes. Majority of the isolates (50/52) in eight genotypes were closely related to SPLCV. Among them, four genotypes from South Carolina with 91-92% sequence identity to the type member of SPLCV-US were considered a new strain; whereas four other genotypes from Mississippi with >95% sequence identity to SPLCV-US were considered variants. In addition, a novel begomovirus was identified in the sample (US:SC:646B-9) from South Carolina, with <89% of sequence identity to all known begomoviruses. Hence, a provisional name Sweet potato leaf curl South Carolina virus (SPLCSCV) is proposed. Moreover, a natural recombinant consisting of two distinct parental genomic sequences from SPLCV and SPLCGV was identified in a sample from Mississippi. The knowledge of greater genetic diversity of begomoviruses on sweetpotato will likely have a major impact on PCR-based virus detection and on disease management practice through breeding for virus resistance.

“End/Tip Rot Diseases of Sweetpotatoes: Current Research Status”

Sandra W. Woolfolk^1,2, Richard E. Baird², Ramon A. Arancibia³, Dorgelis A.Villarroel², and R. Alan Henn²

¹ North Mississippi Research and Extension Center, Mailstop 9655, Mississippi State University, MS 39762

² Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mailstop 9655, Mississippi State University, MS 39762

³ Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863

End/tip rots of sweetpotatoes are an unknown rot complex.  Found during the 2008-2009 growing season, this rot complex coupled with other rots dramatically impacted storage roots and caused substantial economic losses.  A study is currently being conducted to determine the causal agent(s) of these diseases.  Two fields planted with Beauregard varieties, having a history of sweetpotato rot, and with 1-2 years of continuous sweetpotato production were selected.  Bacteria and fungi were isolated from eight sequential sampling periods (from bedding to storage).  Two bacterial and two fungal media are used for isolation.  Bacteria and fungi are currently being characterized using fatty acid methyl esters analyses and morphological features, respectively.  Molecular sequencing techniques will be used to confirm the identification.  Representative tissues from each sample are currently stored in -80°C for further processing (i.e., DNA extraction).  Approximately 2400 isolates of fungi and 2500 isolates of bacteria were collected from sampling period 1-6.  Samples from period 7 are currently being processed.  Several fungal genera tentatively identified included Fusarium (several species), Candida, Curvularia­, Cercosporella, Phoma-like, Aspergillus, and Macrophomina.  Following identification, representative isolates of each taxon (fungi and bacteria) will then be stored in       -80°C as sweetpotato end/tip rot study culture collections.  Isolate screening will be conducted beginning of 2011 for the same species that show the greatest promise as the rot pathogen(s).

“Stress Effects on Sweetpotato Storage Root Rots, Some Preliminary Observations” – Chris Clark, Rebecca Sweany, Washington da Silva; Dept. Plant Pathology & Crop Physiology, and Arthur Villordon; Sweet Potato Research Station, Louisiana State University Agricultural Center.

A complex of sweetpotato storage root rots develops sporadically in the field and in storage.  Soft rotting is apparently triggered by flooding in the field, but it is not clear what contributes to end rot development.  We are trying to assess what pathogens are involved and what environmental conditions lead to development of the different rots.  When Beauregard and Evangeline storage roots from storage were submerged in sterile distilled water in sealed Mason Jars and incubated at 32^oC, a flood-induced soft rot (FISR) developed beginning at lenticels and rapidly rotting entire roots.  FISR began in Beauregard after 4.0 days and in Evangeline after 7.8 days under these conditions but was significantly delayed if roots were surface disinfested with 0.525% NaOCl prior to incubation.  White growth emerged from isolated locations on roots with FISR and consisted of rod-shaped cells about 2 x 5 µm in size with an endospore at the end of many cells.  When Beauregard and Evangeline roots from the same lots were sealed in polyethylene bags and incubated at 32^oC, rots developed from the ends of the roots which were firmer and developed more slowly than FISR.  End rot began in Beauregard after 9.6 days and in Evangeline after 5.2 days.  Macrophomina or Fusarium were isolated from the leading margins of most such roots which eventually developed symptoms consistent with charcoal rot and/or Fusarium root rot.  Surface disinfesting roots prior to incubation in plastic bags had either no effect on onset of end rotting or induced slightly earlier decay than in untreated controls.  This suggests that the causal fungi were already present inside the roots and both fungi were isolated from surface-disinfested slips and crowns at transplanting and harvest, respectively.  While it is clear that stored sweetpotatoes respond very differently to these different artificial stresses, it is not clear how this relates to stress occurring in the field.

“Evaluation of Selected Insecticides for Management of Sugarcane Beetle in Sweetpotato”
T. P. Smith*¹, T. Arnold1. LSU Agricultural Center: *¹Sweet Potato Research Station, Chase, LA.

The sugarcane beetle, (Euetheola humilis rugiceps Burmeister) is a sporadic but significant insect pest affecting sweetpotato in Louisiana and Mississippi. Adult sugarcane beetles feed on sweetpotato roots late during the production season. Sugarcane beetles move into sweetpotato fields during August and September after preplant and layby soil insecticide applications have been applied. Sugarcane beetle feeding damage compromises the aesthetic quality of sweetpotato roots, often leaving them unsuitable for market. Producers currently rely on traditional labeled soil insecticides and planting date recommendations to manage this insect in commercial fields. More information is needed on monitoring techniques and chemical control options for this insect. Several insecticides currently labeled for use on sweetpotato in Louisiana and Mississippi were evaluated in 2009 and 2010 for their efficacy against sugarcane beetle. All pre-plant insecticide treatments were applied the day preceding transplanting. Sweet potato transplants were planted at a rate of 1 plant/ft in plots of 4 rows (centered on 42 inches) x 30 ft on 9 July and 28 May in 2009 and 2010, respectively. Treatments were arranged in a RCB design and replicated four times. Preplant and layby insecticides were applied as a band along the row center to the 2 center rows, and the beds were disked immediately following application. At harvest, roots from the middle rows were dug and 25 roots per plot were chosen at random and evaluated for insect damage after washing. The majority of root damage in both years was attributed to sugarcane beetle. In 2009, total percent insect damage (all species) ranged from 13.00-50.00 percent, whereas sugarcane beetle damage ranged from 8.00-40.00 percent. In 2010 total percent insect damage ranged from 29.00-70.00 percent, whereas sugarcane beetle damage ranged from 11.00-59.00 percent. Applications of Belay 2.13 SC, Lorsban, and Admire Pro resulted in significantly less total soil insect damage and sugarcane beetle damage compared to the non-treated control plots.

“Current Status of Soil Insect Management Research in North Carolina Sweetpotato”

Mark R. Abney, Nancy L. Maxwell, and Rocio Davila. Department of Entomology, North Carolina State University, Raleigh, NC.

Though a variety of soil insects feed on sweetpotato roots, wireworms continue to be the most serious pest of the crop in North Carolina. Current control strategies rely on a combination of pre and post-plant soil incorporated insecticides that target tobacco wireworm, the most common species found in sweetpotato in the state. Research focused on enhancing wireworm management through improved insecticide efficacy has been ongoing at NC State University for a number of years. Recent efficacy trials evaluated new materials including neonicotinoids that may provide alternatives to the organophosphate and pyrethroid insecticides that are presently used. The exotic white grub Plectris aliena caused significant damage to sweetpotato each year since it was first identified in North Carolina in 2006. Understanding the biology of the pest is crucial to developing effective management strategies and is central to research efforts. The beetle appears to have a one year life cycle in North Carolina, and studies show that it is capable of completing development on sweetpotato, corn, soybean and pasture grasses. Severity of damage to sweetpotato varies from field to field and from location to location within a field in a given season. Populations of the insect also change within a given field from one year to the next. Work is in progress to better understand the factor(s) that influence spatial and temporal distribution of the insect in the sweetpotato agroecosystem.

“Effect of Simulated Rainfall and Application Timing on Sweet Potato Tolerance to Dual Magnum”

Donnie K. Miller, Tara P. Smith, T. Arnold, and M. S. Mathews.LSU AgCenter, Baton Rouge, LA 70803.

A field study was conducted in 2010 at the Sweet Potato Research Station near Chase, LA to evaluate the impact of simulated rainfall, herbicide application timing, and Dual Magnum (s-metolachlor) rate on sweet potato growth, development, and yield.  Rainfall simulators were constructed to place each nozzle approximately 214 cm above each row top.  Industrial nozzles that approximated rainfall droplet size, angle, and velocity were used to deliver amounts of 1.3 or 5.1 cm to designated plots immediately after herbicide application.  A factorial arrangement of simulated rainfall amount (1.3 or 5.1 cm), herbicide application timing (at planting, 5 d after planting, or 10 d after planting) and Dual Magnum rate (0, 1067 g ha, or 2135 g ha) replicated four times in a randomized complete block design was utilized.  Plots were maintained relatively weed free by routine hoeing during the growing season.  Parameter measurements included visual plant injury 14, 28, and 42 d after herbicide application.  In addition, scoring measurement for root initiation, based on number observed from one plant per plot, was conducted at approximately 12 d (microscopic evaluation of plant anatomy) and 26 d (visual inspection) after planting.  Machine harvest of plots was conducted 103 d after planting.  Significant herbicide rate by simulated rainfall amount interaction was noted for root initiation data while significant herbicide rate by application timing interaction was noted for yield.

Herbicide application timing did not influence storage root initiation.  At 12 d after planting, averaged across herbicide application timing, storage root initiation with no herbicide averaged 0.9 and 1.5 for the 1.3 and 5.1 cm simulated rainfall amounts, respectively, and was not reduced with Dual Magnum at either rate.  Comparing Dual Magnum rates, however, a reduction in storage root initiation was observed with the high rate (0.8 vs. 1.5) followed by 1.3 cm simulated rainfall but not the 5.1 cm simulated amount (1.2 vs 1.7).  Similarly, at 26 d after planting, storage root initiation averaged 4.7 and 5.9 for no herbicide application, with no reduction observed with Dual Magnum.  Again Dual Magnum at the highest rate resulted in lower storage root initiation at the 1.3 (5.6 vs 6.7) but not 5.1 (5.3 vs 6) cm rainfall amount when compared to the lower rate.

Yield was not impacted by amount of simulated rainfall applied.  Averaged across simulated rainfall amounts, U.S. #1 yield averaged 72, 79, and 87 bu/A where no herbicide was applied for at planting, 5, and 10 d after planting intervals, respectively, and was not reduced with Dual Magnum at either rate.  Similarly, total yield (U.S. #1, canner, and jumbo) with no herbicide application averaged 145, 152, and 148 bu/A for these respective treatment intervals, with no reduction observed following Dual Magnum application.  With respect to both U.S. #1 and total yield, yield was not reduced with the higher rate of Dual Magnum compared to the lower rate.

Post Harvest Physiology, Food Science, and Marketing

“Sweetpotato Storage Study In North Carolina”

Dr. Michael D. Boyette¹, and Jose G. Garzon^1
1 Department of Biological and Agricultural Engineering, North Carolina State University, Box 7625
Raleigh, North Carolina 27695

North Carolina is the largest producer of sweetpotatoes in the US with an annual production of nearly 470 million kg. (NCDACS, 2009) Under optimum storage conditions, sweetpotatoes may be held in marketable condition for longer than 10 months. This allows for orderly marketing throughout the year. In the last 15 years, several hundred long-term storage facilities have been built employing a novel air movement system now termed negative horizontal ventilation (NHV). Most of these facilities are located in North Carolina and other sweetpotato producing areas of the southeastern US. This technology is especially suitable for the large commercial sweetpotato storage facilities now common in the industry. Sweetpotatoes are alive and respire during storage and the rate of respiration, and consequently the weight loss, is proportional to the storage temperature. Since sweetpotatoes are sold by weight, it is beneficial to the grower to minimize weight loss while still preserving a quality product. During 2009-2010 a test was conducted in one of the Universities’ cooler rooms, where five different varieties of sweetpotatoes were placed on electronic scales and the temperature inside the cooler was changed in cycles from 58 to 74 ˚F. Their weight was recorded every hour over a period of 300 days, simultaneously other electronic scales where placed in commercial facilities where temperature is stable during the same period of the test. The data shows the daily weight loss under both circumstances, the difference between varieties, and yields some interesting observations about the influence of genotypes and environmental conditions during long term storage of sweetpotatoes.

“Recent Refinements in Horizontal Ventilation Sweetpotato Storage”

Michael D. Boyette, Department of Biological and Agricultural Engineering, North Carolina State University, Box 7625, Raleigh, North Carolina  27695

In the last twenty years, approximately 15 million bushels of on-farm sweetpotato storage has been built in North Carolina utilizing horizontal ventilation. Horizontal ventilation facilities have also been widely built in other sweetpotato producing states as well as a number of foreign countries. Through cooperation between growers, building contractors, equipment supplier and university researchers, much has been learned that has allowed us to refine the systems that are being presently built in many beneficial ways. Compared to buildings built in the early 1990s, the latest built sweetpotato facilities are larger, more economical, more energy efficient and give a much higher level of environmental control than a few years ago. For example, the incorporation of booster fans has allowed room length to increase to 120 feet or more. The use of supervisory control and data acquisition (SCADA) systems now are widely used to monitor and control room conditions with very little effort. By utilizing variable frequency drives (VFD) on the fan motors, facilities can be more precisely controlled while saving a significant amount of electrical costs. We have also learned to optimally operate these facilities despite variations in harvest conditions or seasonal changes in weather throughout the 10 plus months the sweetpotatoes can be held in storage.

“Long-term storage of sweetpotatoes as related to French fry processing quality”

V. D. Truong¹, Y. T. Pascua¹, R. Reynolds¹, R. L. Thompson¹, L. O. Dean¹, M. D. Boyette², J. R. Schultheis³, G. C. Yencho³, and J. Kimber^4
1USDA-ARS, SAA Food Science Research Unit, ²Department of Biological and Agricultural Engineering, ³Department of Horticultural Science, North Carolina State University, ⁴North Carolina Sweetpotato Commission Foundation Inc., Raleigh, NC 27695

Variation in root quality during long-term storage remains a challenge in commercial production of sweetpotato French fries (SPFF). For commercial success, the product should be of consistent quality regardless of root storage duration. This study aimed to investigate the effect of 1 year storage of sweetpotatoes at 13 ⁰C, 85% relative humidity and processing treatments on SPFF physico-chemical and sensory properties. Samples of stored Covington sweetpotatoes were taken at 4, 7 and 11 months for chemical analyses and processed into SPFF for quality assessment. Reducing sugar and sucrose levels in raw roots varied between 1.3-1.9% and 4.1-4.9% during storage while starch and carotene content decreased from 6.1% to 2.9% and 7.2 to 6.6 mg/100g fresh weight (fw), respectively. The developed process for SPFF involved blanching sweetpotato strips, treating with sodium acid pyrophosphate, partially drying, coating with carbohydrate-based batter and frying at 165 °C. Neither coating nor root storage time had significant effect on lightness, hue, firmness or oil content (9.6%) of SPFF. Overall consumer liking, perceived interior firmness and sweetness scores of the coated SPFF processed from 4-, 7- and 11-month stored roots were not significantly different (p > 0.05), and averaged at 6.8, 4.2 and 5.2, respectively. The results demonstrate that consistent quality SPFF can be produced year round from sweetpotatoes stored under appropriate conditions.

Breeding, Genetics, and Molecular Biology

“Somatic Embryogenesis and Genetic Transformation Of Multiple Sweetpotato [Ipomoea batatas L. (Lam)] Cultivars for Enhanced Productivity, Nutritional and Health Values”

Steven Samuels*¹, Marceline Egnin¹, Jessica Scoffield², Ben Bey¹, Sy Traore¹, C. S. Prakash¹, Jesse Jaynes¹ and Jacquelyn Jackson¹

¹Tuskegee University, Plant Biotech and Genomics Research Laboratory, Tuskegee, AL 36088, ²²Auburn University, AL36830

We have developed efficient somatic embryogenesis and genetic transformation systems, applicable across a range of sweetpotato genotypes, to facilitate the genetic manipulation and improvement for better human nutrition and health.  The three-stage somatic embryogenesis protocol includes a 3-week initiation on callus production media followed by 2 to 4 weeks culture on embryo production media with 2.5 mg/L ABA, resulting in multiple embryos converting into plantlets.  This protocol has serves to investigate several factors enhancing Agrobacterium-mediated transfer of foreign genes to sweetpotato cells utilizing an intron-containing b-glucuronidase (uid-A) gene under the transcriptional control of CaMV 35S promoter.  The use of cocultivation media containing high auxin in combination with low cytokinin (BAP at 0.25 mg/L) levels promoted higher transformation rates than either hormone-free or 2,4-D only medium.  Pre-culture of explants prior to infection and cocultivation significantly decreased the number of transiently transformed blue zones.  The optimized protocol was used to obtain transient transformation frequencies of all cultivars tested ranging from 12% to 87% for leaf explants, which were found to be most responsive to Agrobacterium-mediated transformation and induction of somatic embryos (50-100%) as compared to petiole and stem explants.  The presence of the transgene in regenerated plants was confirmed by histochemical GUS assay and Southern blot analysis.  Beauregard, NCC58 and PI 318846-3 (D-3) were more amenable to Agrobacterium transformation (68- 87%) than other cultivars tested.  Disarmed Agrobacterium tumefaciens strains EHA101 and EHA105 were superior in facilitating the transfer of uid-A-intron gene to sweetpotato cells than strains and C58.  EHA105, harboring pGPTV/jc41N or pGPTV/jc41ND containing synthetic lytic peptide gene constructs, that are capable of inhibiting HIV progression, were utilized to engineer sweetpotato as plant-based therapeutic treatments.  Twenty-four putative transgenic plantlets were developed from fifty-five kanamycin resistant embryos with frequencies of 45% for jc41N and 58% for jc41ND.  Integration of the trangenes in D-3 is currently under investigation through PCR, qRT-PCR, and Southern analyses. Funded by NASA/USDA-EVANS ALLEN/NIH.

“Comparative Gene Expression and the Physiological Role of t-Zeatin Riboside (ZR) During Storage Root Initiation and Enlargement of In Vitro and Hydroponic Cultured Sweetpotato”

Marceline Egnin*¹, Latrice Crawford¹, Jessica Scoffield², Ben Bey¹, Desmond Mortley¹, Hui Gao², Frieda Sanders¹, Sy Traore¹, John Williams¹, Carol Williams¹ and Sherwin Jack¹

¹Tuskegee University, Plant Biotech and Genomics Research Laboratory, Tuskegee, AL 36088. E-mail: megnin@tusk.edu, ²Auburn University, AL36830

Storage root (SR) development is an important, yet poorly understood process determining yield in root crops.  Recent studies utilized a specific developmental time point of soil-grown sweetpotato to elucidate anatomical, physiological, hormonal and molecular characteristics controlling SR initiation and enlargement.  Early developmental time points of in vitro sweetpotato micro-storage roots (MSR) formation represent a promising tool for a clean (disease-free) visual screening for molecular elucidation of processes in yield and transgene expression.  Elite sweetpotato genotypes were screened for micro-cutting length and explant position on Heller and Hoagland media with differing hormonal and carbon sources, and photoperiods to facilitate MSR formation for anatomical, hormonal and gene expression studies.  Foil wrapped to the media level overlaid by 2% charcoal prevented light entry into the root production zone.  Beauregard, NCC58, J66-6 and ROJO had 100% MSR initiation and bulking with root color change in Hoagland compared to Jewel and TU-155 (75%), and Mogamba and Zappallo (50%).  Cuttings vertically inverted developed multiple MSR regardless of media or genotypes.  Dark conditions at the root zone promoted faster root initiation and bulking than light.  Hoagland developing and matured MSR results were similar to field and NFT conditions in the following: 1) starch content and granule distribution in anatomical structures; 2) sporamin and ß-amylase detected by western increased as root development progressed; and 3) t-zeatin riboside (ZR) accumulation patterns (0.6-30 pmol/ml) were delayed 2 weeks over field/NFT.  NCC-58, TU82-155 and J6/66 cDNA-AFLP identified 98 transcripts differentially (TDF) expressed during early stages of MSR. Selected TDFs predicted functions were homologous at 71% to Ipomoea batatas mRNA clone-IT443 3′ end sequence expressed in Kokei-14 mature tuberous root.  Nine MSR TDF clones were catalogued as gene regulation, cell division and expansion, signal transduction, tumorigenesis and sporamin accumulation. Based on similar developmental patterns to field/NFT, in vitro MSR system is an excellent alternative for gene expression profiling studies as the root undergoes initiation.  Funded by NASA, USDA/CSREES and GWCAES.

“Functional characterization and comparative analysis of the sweetpotato root transcriptome”

Julio Solis¹, Nurit Firon², Arthur Villordon³, and Don Labonte¹

¹School of Plant, Environmental, and Soil Sciences. LSU AgCenter, Louisiana State University. ²Institute of Plant Sciences, The Volcani Center, Agricultural Research Organization, Bet Dagan, 50250. ³Sweet Potato Research Station, LSU AgCenter, Louisiana State University.

The goal of this study was to make a comparative genomic analysis of 454 sequences derived from initiated (early developing) storage roots and fibrous roots and to annotate sequences found in sweetpotato.  There is currently no unified database presenting the functional annotation and characterization of genes relating to cellular processes and metabolic pathways in sweetpotato.  The sequences were assembled into a unigene set (~ 110,000 sequences) and compared against a set of sweetpotato sequences from available public and private databases from root and non-root tissues. We identified 101,409 sequences greater than 100 nucleotides, of which 37,697 are new when compared to the sweetpotato gene index (Schafleitner et al, 2010).  Approximately 80,000 are new when compared to public sequences derived from either developing storage roots, fibrous or formed storage root tissues. BLASTX search with selected proteins (TAIR10 and a set of Uniprot from Solanales order) annotated 68,933 sequences with an e-value of 1e-06 whereas 32,477 sequences remain unknown. Blast2GO was used for functional characterization of the transcriptome. This analyses found 2,656 sequences associated with transporter activity, 1,949 for transcription regulatory activity, and 566 for molecular transducer activity. KEGG mapping in metabolic pathways analysis showed that the majority of sequences are in starch and sucrose metabolism (877), biosynthesis of plant hormones (1,078), biosynthesis of phenylpropanoids (863) and  biosynthesis of secondary metabolites (2,248).  Interestingly, clustering all sequences from root libraries using blastclust revealed 117,315 clusters for the root transcriptome, which requires further characterization. Long term this effort will help  build a functional genomic database of the sweetpotato transcriptome, a more inclusive microarray slide, and permit gene expression profiling based on identified and predominant functionality of candidates genes associated with storage  root formation.

Poster presentations

“2010 Product Evaluation for Reniform Nematode Suppression in Mississippi Delta Sweetpotato Production”

Larry Adams, USDA-ARS, SIMRU. Stoneville, MS

The reniform nematode, Rotylenchulus reniformis, can cause significant losses in sweetpotato, Ipomoea batatas, production in the Mississippi Delta. Reduction in yield due to the presence of above threshold populations of the reniform nematode has been documented across the historical sweetpotato producing areas in the United States. Traditionally, high numbers of the reniform nematode are encountered in the sandy/silt loam delta soils that are suitable for sweetpotato production. During the 2010 growing season USDA, ARS, SIMRU compared four products to suppress the reniform nematode in Mississippi Delta sweetpotato fields. Soil samples were taken twice during the season to asset reniform populations. Yield and quality of the sweetpotatoes from each treatment was recorded and analyzed.

“Insecticide Application Method and Chemistry Evaluation for Sweetpotato Production in the Mississippi Delta”
Larry Adams, USDA-ARS, SIMRU, Stoneville, MS

In the Mid-South soil insects can cause significant losses in sweetpotato, Ipomoea batatas, production. This has been documented across the sweetpotato producing areas in the Mississippi and Louisiana delta regions with total field losses due to extremely high populations of root feeding pest. Mississippi sweetpotato growers have typically incorporated insecticides into the row beds prior to transplanting slips to control soil pest. In 2010 USDA, ARS, SIMRU completed a study evaluating ten insecticides that were incorporated into the row bed and five insecticides were evaluated by the delivery method, incorporation prior to transplanting the slips or mixed with the transplant water when transplanting the slips. Insect damage, yield and quality of the sweetpotatoes from each treatment was recorded and analyzed.

Production, Physiology, and Plant/Seed Production

Ramon Arancibia (Miss. State Univ.), raa66@msstate.edu

1. “Sweetpotato Color Analyses” D. Michael Jackson. U.S. Vegetable Laboratory.

2.“Temperature effects on sweetpotato storage root growth and development”K. Raja Reddy, Bandara Gajanayake, Mark Shankle, Ramon Arancibia and Arthur Villordon

Photo contact: R. Reddy, Miss. State Univ.

3.“Interactive effects of temperature and elevated carbon dioxide on early-season sweetpotato growth and development” Bandara Gajanayake , K. Raja Reddy, Mark Shankle and Ramon Arancibia

Photo contact: R. Reddy, Miss. State Univ.

4.“The effect of salty water irrigation on sweetpotato storage root formation” Nurit Firon¹, Zion Shemer², Yanir Kfir¹, Michal Amichai², Etan Pressman¹ and Levia Althan¹

¹ Inst. of Plant Sciences, The Volcani Center, ARO, P.O. Box 6, Bet Dagan, 50250, Israel.

² Ramat Negev Experimental Station, M. P. Haluza, 85515, Israel.

Photo contact: N. Firon, The Volcani Center

5. “Further calibration and validation of a Bayesian belief network model representing the relationship between fresh market yield and agroclimatic variables known to influence storage root initiation in ‘Beauregard’ sweetpotato: soil moisture and planting density” A. Villordon,¹ J. Solis,² D. LaBonte,² C. Clark³, and R. Sheffield ⁴

¹LSU AgCenter Sweet Potato Research Station, ²LSU AgCenter School of Plant , Environmental, and Soil Sciences. ³LSU AgCenter Department of Plant Pathology and Crop Physiology. ⁴LSU AgCenter Department of Agricultural and Biological Engineeering

Photo contact: A. Villordon, LSU AgCenter

6. “Preliminary experience using a minirhizotron-based system for characterizing adventitious root development during the storage root initiation period: prospects and problems” A. Villordon,¹ J. Solis,² D. LaBonte²

¹LSU AgCenter Sweet Potato Research Station, ²LSU AgCenter School of Plant , Environmental, and Soil Sciences.

Photo contact: A. Villordon, LSU AgCenter

7. “Efficacy of nematicides and metam sodium on field production of sweetpotatoes in California” Scott Stoddard, UC Cooperative Extension, Merced County.

Photo contact: S. Stoddard, UC-Davis

8. “First year results of various cover crops on Mississippi sweet potato production” Jeff Main, Ramon Arancibia and Mark Shankle. Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863

9. “Incidence of skinning and tip/end rot in sweet potato with pre-harvest applications of Ethephon” Ramon Arancibia, Jeff Main and Mark Shankle. Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863

10. “Skin and wound healing characteristics in sweet potato” Nestor Bonilla, Ramon Arancibia and Jeff Main. Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863

Insect, Disease, and Weed Management

Mark Abney (NC State University), mark_abney@ncsu.edu

1. “Recent Advances in the Molecular Characterization of Sweetpotato Begomoviruses”Kai-Shu Ling*¹ and ShuoCheng Zhang^{2 1} U.S. Vegetable Laboratory, United States Department of Agriculture, Agricultural Research Service, 2700 Savannah Highway, Charleston, SC 29414, ² Center for Biotechnology and Genomics, Alcorn State University, Alcorn State, MS 39096, USA.

Photo contact: Kai-Shu Ling, U.S. Vegetable Lab.

2.“End/Tip Rot Diseases of Sweetpotatoes: Current Research Status” Baird, R.E., Woolfolk, S.W., Arancibia, R.A., Villarroel, D.A., and Henn, R.A.

3. “Stress Effects on Sweetpotato Storage Root Rots, Some Preliminary Observations” – Chris Clark, Rebecca Sweany, Washington da Silva, Dept. Plant Pathology & Crop Physiology, and Arthur Villordon, Sweet Potato Research Station, Louisiana State University Agricultural Center

Photo contact: C. Clark, LSU AgCenter

4. “Evaluation of Selected Insecticides for Management of Sugarcane Beetle in Sweetpotato” T. P. Smith*¹, T. Arnold¹. LSU Agricultural Center: *¹Sweet Potato Research Station, Chase, LA

Photo by Gerald Lenhard.

5. “Current Status of Soil Insect Management Research in North Carolina Sweetpotato”

Mark R. Abney, Nancy L. Maxwell, and Rocio Davila. Department of Entomology, North Carolina State University, Raleigh, NC.

6. “Management of soil insect pests of sweetpotato in Louisiana.”
Rick Story, LSU AgCenter

7. “Effects of Dual Magnum (s-metolachlor) rate and timing on sweetpotato storage roots” D.W. Monks, K.M. Jennings, S.L. Meyers and L. Brumfield III. NC State University, Raleigh.

8. “Effect of simulated rainfall and application timing on sweet potato tolerance to Dual Magnum” Donnie Miller and Tara Smith. LSU AgCenter Northeast Research Station and LSU AgCenter Sweet Potato Research Station.

9. “Delayed-PRE herbicide systems in sweetpotato”

Mark W. Shankle and Trevor F. Garrett. Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863.

10. “Herbicide symptomology in sweetpotato varieties”

Mark W. Shankle and Trevor F. Garrett. Pontotoc Ridge-Flatwoods Branch Experiment Station, North Mississippi Research and Extension Center, Mississippi State University, Pontotoc, MS 38863.

Post Harvest Physiology, Food Science, and Marketing

Scott Stoddard (UC Davis), csstoddard@ucdavis.edu

1. “Sweetpotato Storage Study In North Carolina” Michael D. Boyette, and Jose G. Garzon, Department of Biological and Agricultural Engineering, North Carolina State University, Box 7625, Raleigh, North Carolina 27695

Photo contact: J. Garzon, North Carolina State Univ.

2. “Effect of curing and ethylene treatment on sensory and other quality traits of sweet potatoes” Juan L. Silva, Ershad Sheibani, Ramon Arancibia, Taejo Kim, Jeff Main

3. “Sweet potato collaborators baking and microwave quality- 2010 trials” Juan L. Silva, Ramon Arancibia, Ershad Sheibani, Jeff Main

4. “Long-term storage of sweetpotatoes as related to French fry processing quality”V. D. Truong¹, Y. T. Pascua1, R. Reynolds¹, R. L. Thompson¹, L. O. Dean¹, M. D. Boyette², J. R. Schultheis³, G. C. Yencho³, and J. Kimber⁴. ¹USDA-ARS, SAA Food Science Research Unit, ²Department of Biological and Agricultural Engineering, 3Department of Horticultural Science, North Carolina State University, ⁴North Carolina Sweetpotato Commission Foundation Inc., Raleigh, NC 27695

Photo contact: V.D. Truong, USDA-ARS, SAA Food Science Research Unit

5. “Recent Refinements in Horizontal Ventilation Sweetpotato Storage” Michael Boyette. Department of Biological and Agricultural Engineering. North Carolina State University.

Photos contact: M. Boyette, North Carolina State Univ.

Breeding, Genetics, and Molecular Biology

Chris Clark (LSU AgCenter), cclark@agcenter.lsu.edu

1. “Somatic Embryogenesis and Genetic Transformation Of Multiple Sweetpotato Cultivars for Enhance Productivity, Nutritional and Health Values” Steven Samuels*, Marceline Egnin, Sy Traore, Jesse Jaynes and Jacquelyn Jackson. Tuskegee University, Plant Biotech and Genomics Research Laboratory, Tuskegee, AL 36088

2. “Comparative Gene Expression and the Physiological Role of t-Zeatin Riboside (ZR) During Storage Root Initiation and Enlargement of Invitro- and Hydroponic-Cultured Sweetpotato” Marceline Egnin*¹, Latrice Crawford¹, Jessica Scoffield², Ben Bey¹, Desmond Mortley¹, Frieda Sanders¹, Sy Traore¹, Hui Gao², and Sherwin Jack¹, ¹Tuskegee University, Plant Biotech and Genomics Research Laboratory, Tuskegee, AL 36088²Auburn University, AL

Photo contact: M. Egnin, Tuskegee University.

3.“Functional characterization and comparative analysis of the sweetpotato root transcriptome”

Julio Solis¹, Nurit Firon², Arthur Villordon³, and Don Labonte¹

¹School of Plant, Environmental, and Soil Sciences. LSU AgCenter, Louisiana State University. ²Institute of Plant Sciences, The Volcani Center, Agricultural Research Organization, Bet Dagan, 50250.³Sweet Potato Research Station, LSU AgCenter, Louisiana State University.

Poster Presentations:

Insecticide Application Method and Chemistry Evaluation for Sweetpotato
Production in the Mississippi Delta
Larry Adams, USDA-ARS, SIMRU, Stoneville, MS

2010 Product Evaluation for Reniform Nematode Suppression in
Mississippi Delta Sweetpotato Production
Larry Adams, USDA-ARS, SIMRU, Stoneville, MS