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  • Author or Editor: Arthur Villordon x
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Clonal propagation assures the maintenance of genetic purity of a sweetpotato variety. The existence of foundation seed programs further contributes to the conservation of favorable genetic constitution in a commercial cultivar. However, the improvement of current maintenance procedures is necessary as shown by the occurrence of mutations and the decline of certain commercial varieties. Information on the nature and extent of changes in sweetpotato would therefore be useful in this regard.

`Jewel' clones obtained from eight state foundation seed programs were subjected to yield tests and a RAPD-based assay. Differences in nearly all yield grades were detected during the 1991, 1992, and 1993 seasons. The yield of U.S. No. 1 grade roots varied from 27% to 46%. The quality factors measured also varied: % alcohol insoluble solids varied by 13%, while sucrose ranged from 9.6% to 19%. Total DNA was extracted from each clone and assayed against 40 primers. All primers produced amplified fragments. A total of 110 reproducible bands was generated by 38 primers. Putative polymorphic markers were scored in 21 (18.58%) of these bands based on the presence or absence of amplified products. The results suggest an underlying cause for the variability observed in phenotypic traits within sweetpotato clones.

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Our research examined whether plants originating from adventitious sprouts from fleshy sweetpotato roots are genetically more variable than plants that arise from pre-existing meristematic regions, i.e., nodes. Our study compared one plant each of `Jewel', `Sumor', and L87-95 clonally propagated for seven generations both nodally and through adventitious sprouts. PCR-based analysis of 60 samples (10 nodal and 10 adventitiously derived plants/genotype) showed 20% polymorphism among adventitious materials vs. 6% among nodally derived plants. An “analysis of molecular variance” showed that differences between propagation methods accounted for 30% of the total marker variability. Our results support previous findings that, relative to non-meristematic materials, meristematic regions strictly control cell division and DNA synthesis that exclude DNA duplication and other irregularities.

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The Louisiana Dept. of Agriculture and Forestry (LDAF) conducts sweetpotato weevil [SPW, Cylas formicarius (Fabricius)] monitoring in support of the statewide SPW quarantine program. The monitoring activity primarily involves a statewide pheromone-based trapping process that generates trap data for sweetpotato beds and production fields. We conducted GIS analysis of SPW trap data, collected over three years, to assess the potential use of GIS tools in managing and interpreting the data. The LDAF has already generated shapefiles for all beds and fields in each of three years, facilitating GIS analysis. However, trap data was manually collected and statewide data was compiled and stored in spreadsheet files. Trap data was mapped to specific beds and fields in each of three years, generating layers that clearly showed fields and parishes that reported high trap counts. GIS analysis showed potential SPW “hotspots” in each year, indicating that certain beds or fields are more prone to SPW infestation than others. This information can be useful in planning SPW management strategies by growers and other stakeholders. The GIS database also provides the foundation for the development of descriptive and predictive models of SPW occurence in Louisiana. Compiling the SPW trap data into a GIS database allows the data to be distributed over the Internet, facilitating real-time access by stakeholders.

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The Louisiana Department of Agriculture and Forestry (LDAF) conducts sweetpotato weevil (SPW) (Cylas formicarius Fabricius) monitoring as part of the statewide SPW quarantine program. This activity involves a statewide pheromone-based trapping program that monitors sweetpotato beds and production fields. We conducted GIS analysis of SPW trap data, collected over three years, to assess the potential use of publicly available GIS tools in managing and interpreting the data. Trap data was mapped to specific beds and fields in each of three years, generating layers that clearly showed fields and parishes that reported high trap counts. GIS analysis showed potential SPW hotspots in each year, indicating that certain beds or fields are predisposed to SPW infestation than others. This information can be useful in planning SPW management strategies by growers and other stakeholders. The GIS database also provides the foundation for the development of descriptive and predictive models of SPW occurence not only in Louisiana, but in other states where SPW is a potential pest. For example, using presence data for Louisiana and Genetic Algorithm for Rule Set Prediction (GARP), a GIS-based ecological niche modelling tool, we were able to generate predicted distribution using mean minimum temperature for January as the predictor variable. Although additional work is needed to identify other predictor variables and verify the models, the results demonstrate the potential use of GIS-based tools for generating warnings or advisories related to SPW.

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The use of handheld computers such as personal digital assistants (PDAs) represents a feasible method of automating the transfer of files to computers for archiving and statistical analysis. Data collected using the PDA can be transferred directly to a database program on a desktop computer, virtually eliminating errors associated with the reentry of manually collected data. These devices are highly portable and can be housed in protective cases, enabling data collection even in inclement environments. The availability of handheld database programs that permit the development of electronic forms further makes the PDA a viable data collection platform for scientific research. These database applications not only allow novice users to develop customized forms that facilitate the recording of alphanumeric data; these applications also synchronize directly with current desktop-based database and spread-sheet applications. We used Microsoft Access database tables, along with Visual CE, a PocketPC database application, to generate electronic forms for collecting data from research trials conducted in 2003. To facilitate comparison with manual data collection, we also recorded observations using “pen and paper” methods. We found no differences between both methods in the length of time required to enter observations. However, the PDA transferred the data to a computer 600% faster relative to the manual reentry method. Using the handheld computer, field data was immediately available for compilation and statistical analysis within minutes of completing the data gathering process, at the same time ensuring the integrity and continuity of the files.

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The primary objective of this work was to generate species-specific information about root architectural adaptation to variation in boron (B) availability at the onset of storage root formation among three sweetpotato [Ipomoea batatas (L.) Lam] cultivars (Beauregard = BX; Murasaki = MU; Okinawa = OK). Three B levels were used: 0B (B was omitted in the nutrient solution, substrate B = 0.1 mg·kg−1), 1XB (sufficient B; 0.5 mg·kg−1), and 2XB (high B; 1 mg·kg−1). The check cultivar BX showed evidence of storage root formation at 15 days in 0B and 1XB, whereas cultivars MU and OK failed to show evidence of root swelling. The 1XB and 2XB levels were associated with 736% and 2269% increase in leaf tissue B in BX, respectively, relative to plants grown in 0B. Similar magnitudes of increase were observed in MU and OK cultivars. There were no differences in adventitious root (AR) count within cultivars but OK showed 25% fewer AR numbers relative to BX across all B levels. 0B was associated with 20% and 48% reduction in main root length in BX and OK, respectively, relative to plants grown in 1XB and 2XB. 2XB was associated with a 10% increase in main root length in MU relative to plants grown in 0B and 1XB. 0B was associated with reduced lateral root length in all cultivars but the magnitude of responses varied with cultivars. These data corroborate findings in model systems and well-studied crop species that B deficiency is associated with reduced root growth. These data can be used to further understand the role of cultivar-specific responses to variation in B availability in sweetpotato.

Open Access

The growing demand for sweetpotato French fry and other processed products has increased the need for producing storage roots of desired shape profile (i.e., blocky and less tapered). Length-width ratio (LW) is the current de facto standard for characterizing sweetpotato shape. Although LW is sensitive and descriptive of some types of shape variability, this index may be inadequate to measure taper and other subtle shape variations. Prior work has shown that surface area (SA) and volume (VOL) are important shape descriptors but current direct measurement methods are tedious, inconsistent, and often destructive. A low-cost three-dimensional (3D) scanner was used to acquire digital 3D models of 210 U.S. No. 1 grade sweetpotato storage roots. The 3D models were imported into Meshmixer, a free software for cleaning and processing 3D files. Processing steps included gap filling and rendering the models water-tight to facilitate VOL measurements. The software includes a tool that enables automatic measurements of length (L), width (W), SA, and VOL. LW and SA-VOL ratio (SAVOL) were subsequently calculated. Separately, a digital caliper was used for manual measurements of L and W. The shrink-wrap method was used to measure SA, and water displacement was used to measure VOL. 3D scanner-based and manual L measurements showed high correlation, whereas VOL was lowest. Principal component analysis (PCA) of 3D scanner-based measurements showed that the first two principal components (PCs) accounted for 96.2% of the total shape variation in the data set, named Ib3D. The first PC accounted for 62.15% of the total variance, and captured variation in storage root shape through changes in VOL, SA, SAVOL, and W. The second PC accounted for 34.4% of the variance, and the main factors were LW and L. Most storage root samples that were classified as processing types were located in the fourth quadrant. The methods described in this work to nondestructively acquire 3D models of sweetpotato also can be adopted for analyzing shape in other horticultural produce like fruits, vegetables, tubers, and other storage roots that meet the specifications for 3D scanning. The data support the hypothesis that knowledge of variables that determine storage root L and W can lead to the development of methods and approaches for enhanced processing product recovery and size assortment for fresh market.

Open Access

This study characterized the influence of nitrogen (N) rates and variation in local availability on root architecture as measured by lateral root (LR) development attributes during the onset of the storage root (SR) initiation stage in ‘Beauregard’ sweetpotato adventitious roots (ARs). In N rate experiments, plants grown without fertilizer N showed significantly lower values for all measured LR attributes compared with fertilized plants. Total first- (1LR) and second-order LR (2LR) length increased by 78% and 2873%, respectively, as N was increased from 0 to 50 kg·ha−1. Total 1LR and 2LR number increased by 32% and 1465%, respectively. Increasing the N rates to 100 and 200 kg·ha−1 did not result in further increases for all LR attributes measured. There were no differences in AR number between untreated controls and plants fertilized with 50 kg N/ha. However, the number of ARs increased by 65% when fertilizer N was increased from 50 to 100 kg·ha−1. Increasing the rate to 200 kg·ha−1 did not result in further increases in AR number. In split-root experiments, roots grown in the compartment with 50 kg N/ha had 135% and 2916% increase in total 1LR and 2LR length, respectively, compared with roots grown in the compartment without fertilizer N. Total 1LR and 2LR number increased by 110% and 2114%, respectively. There were 111% more ARs in the fertilized compartment relative to the unfertilized compartment. There were no differences in LR attributes and AR number between compartments that received similar fertilizer N rates. In fertilizer placement experiments, there were no differences in LR attributes between pre-mixing fertilizer N and placement of fertilizer ≈4 cm below the surface of the growth substrate. There were also no differences between the unfertilized control and placement of fertilizer ≈4 cm from the bottom of the pot. Plants grown in substrate with pre-mixed N showed 38% and 342% increase in 1LR and 2LR length, respectively, relative to the bottom placement of N. Total number of 1LR and 2LR in the growth substrate with pre-mixed N increased by 30% and 312%, respectively, relative to the bottom placement of N. These results represent the first evidence for the association between sweetpotato root architectural attributes and variation in N rate and localized availability. These results are also consistent with findings in model systems in which local N presence is necessary for LR development. This information can be used to further optimize SR yield by helping to ensure the availability of N at the optimum rate across time and space.

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This study aimed to investigate the effect of 1-methylcyclopropene (1-MCP) on adventitious rooting in two sweetpotato cultivars. Experiments with ‘Beauregard’ and ‘Evangeline’ sweetpotato cuttings revealed differential adventitious root (AR) emergence responses to 1-MCP application. ‘Beauregard’ AR count and length decreased with 1-MCP application in two of four experiments. In contrast, 1-MCP did not influence ‘Evangeline’ root count. However, ‘Evangeline’ root length decreased in three of four experiments. Trypan blue staining of ‘Beauregard’ nodal tissue with delayed AR primordia emergence showed localized dead tissue in the general area where ARs emerge. The degree of staining appeared to correspond with the stage of AR emergence with the staining becoming more intense around the time an AR primordium eventually emerged through a crack in the epidermis. This response agrees with reported results of ethylene-mediated AR emergence in other plant species. These results also appear to suggest that ‘Beauregard’ and ‘Evangeline’ cuttings differ in ethylene sensitivity. This represents the first evidence of genotype-specific ethylene involvement in adventitious rooting of sweetpotato cuttings.

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A prototype phenology-driven Bayesian belief network (BBN) model, named BxNET, was developed to represent the relationship between fresh market yield (U.S. #1 grade) and agroclimatic variables known to influence the critical storage root initiation stages in ‘Beauregard’ sweetpotato. This data-driven model was developed from experimental data collected over 3 years of field trials in which management variables were kept as uniform as possible. The BBN was developed assuming that soil moisture measured at the 15-cm depth was not a limiting variable during the first 20 days after transplanting, during which the onset of storage root initiation determined the majority of storage root yield at harvest. The absence of influence from weeds, disease, insect pests, and chemical injury was also assumed. Accuracy of the fully parameterized working prototype was estimated through leave-one-out cross-validation (14% error rate), validation on an independent test data set (20% error rate), and area under the receiving operator characteristic curve (0.59) analysis. As a result of its empirical nature, BxNET is only applicable to the cultivar, location, and the limited set of environmental (air temperature, soil temperature, relative humidity, solar radiation) and management variables as defined in the 3-year study. This beta-level model can serve as a foundation for the development of a final working model through further testing and validation. Additional validation data may require revision of the current model structure and conditional probabilities. These validation studies will also allow the model to be used in other locations. BxNET can be expanded to include other causal variables such as weed incidence, disease presence, insects, and chemical injury. Such an expansion can lead to the development of a model-based decision support system for sweetpotato production. Such a system can help model alternative management scenarios and determine the most reasonable management interventions to achieve optimum yield outcomes under different agroclimatic conditions.

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