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Arthur Villordon*, Jason Franklin and Don LaBonte

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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Arthur Q. Villordon and Don R. LaBonte

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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Douglas Miano, Don LaBonte and Christopher Clark

Sweetpotato is an important staple food crop in Sub-Saharan Africa, with production being concentrated in East Africa, particularly around Lake Victoria. Productivity of the crop is greatly constrained by viral diseases. Four main viruses have consistently been detected from various surveys done in the region viz., sweetpotato feathery mottle virus (SPFMV), sweetpotato chlorotic stunt virus (SPCSV), sweetpotato mild mottle virus (Sp.m.MV), and sweetpotato chlorotic fleck virus (SPCFV). The most severe symptoms have been caused by co-infection with SPCSV and SPFMV, resulting in the synergistic sweetpotato virus disease (SPVD). Some local sweetpotato genotypes have been reported to recover from, or have localized distribution of SPVD, suggesting that the disease is not fully systemic. This has led to the suggestion that uninfected cuttings may be obtained from previously infected plants. Experiments were set to determine the possibility of obtaining cuttings long enough for propagation that are free from virus infection. This would form a basis for recommending to the local small-holder farmers of a way to reduce losses due to the disease. Field-grown sweetpotato vines were cut into three pieces (15, 15–30, and >30 cm from the apex) and tested for SPCSV and SPFMV. Nine genotypes were selected from a group of 21 local clones and used for this study. The two viruses were equally present in all the three sections of infected vines, indicating that it is not easy to obtain a virus-free cutting for field propagation from an infected vine. Virus assays in the past has mainly been limited to the use of serological methods. Use of PCR resulted in detection of begomoviruses infecting sweetpotatoes for the first time in the region.

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Arthur Villordon, Jason Franklin and Don LaBonte

Handheld computing devices, such as personal digital assistants (PDAs), can potentially reduce repetitive tasks that pervade data collection activities in horticultural research. PDA-collected records are electronically transferred to a desktop computer, eliminating manual reentry as well as the need of reviewing for incorrect data entries. In addition, PDAs can be enclosed in protective cases, enabling data collection in inclement weather. Visual CE-generated database forms installed on PDAs were used to electronically collect data from research trials conducted in 2003. The records were subsequently transferred to Microsoft Access desktop database tables for archiving and subsequent statistical analyses. Data for certain trials were also manually collected using paper forms to facilitate comparison between manual and PDA-assisted data collection methods under controlled conditions. Using paired samples analysis, we determined that electronic transfer of records reduced the time required to store the records into desktop computer files. Manual and PDA-based recording methods did not vary in the time required to enter numerical measurements. Our experience demonstrates that off-the-shelf software and consumer PDA devices are viable options for data collection in research. PDA-assisted data collection is potentially useful in situations where remote, site-specific records need to be merged into a central database and where standardized measurements and observations are essential for performing analysis.

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Durel J. Romaine and Don R. LaBonte

Narrow-sense heritability (h2) estimates for sugars were determined to assess the feasibility of breeding for a sweeter baked sweetpotato. Roots of parents and half-sib progeny were baked (190°C for 75 minutes) 16 weeks after harvest. Sugars from 10 gram root samples were extracted in ethanol for HPLC sugar quantification. Alcohol insoluble solid (AIS) residues (starch) were also measured from the samples. Dry matter was determined on a separate 10-g sample. Narrow-sense heritability estimates based on variance components analysis for AIS and percent dry matter were 0.20 and 0.32, respectively. Estimates for sugar data were 0.05 for sucrose, 0.52 for maltose, and 0.52 for total sugars (fructose, glucose, sucrose and maltose). These heritability estimates for maltose and total sugars imply a breeder could expect a moderate gain in sweetness over several cycles of selection.

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Mario I. Buteler, Don LaBonte and Raul Macchiavelli

The breeding of new sweetpotato varieties is a highly inefficient process, confounded by incompatibility, poor fertility, open-pollination, and its hexaploid nature. Upwards of 12 to 20 lines are currently combined in open-pollinated nurseries based on good horticultural characteristics. Most progeny after several years of selection can be traced back to just three or four maternal lines. A method that would identify the paternal parent of superior progeny would enable breeders the ability to combine parents that exhibit superior combining ability in more-efficient, smaller nurseries. The objective of this work is to explore by means of computer simulation the application of genealogy reconstruction techniques on hexaploid individuals with PCR-based data. The progeny obtained on each female parent is fractionally assigned to each male with non zero exclusion probability proportional to its paternity likelihood. Computer simulations show that at least five different alleles per loci are needed to reach a reasonable discriminatory level. Also, the number of loci scored should not be less than 20. An increment in the number of alleles or loci increases the discriminatory power; but, the number of alleles produces a far more important effect than the number of loci.

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Arthur Villordon, Don LaBonte and Julio Solis

A scanner-based minirhizotron (MR) system detected initial adventitious root (AR) development associated with transplant establishment. The system also documented the transition of ARs into pencil roots (PRs) and, in some cases, storage roots (SRs). In general, the MR system underestimated destructive sampling-based (DS) estimates of newly initiated AR (NAR), PR, and SR counts. Angled or vertical single sampling tubes underestimated NAR count by 85% and 79%, respectively. Regardless of installation position, single tube-based measurements underestimated PR and SR count by 83% and 95%, respectively. However, it was found that two vertically installed tubes underestimated NAR count by only 48%. The potential ability of paired sampling tubes to discriminate NAR count differences in response to experimental treatments was confirmed in a simple rain shelter experiment. The paired MR and DS systems detected 83% and 56% reduction in NAR count among plots with rain shelters, respectively. However, it appeared 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 ongoing and future studies that aim to qualitatively and quantitatively document sweetpotato AR system response to agroclimatic variables and management interventions during the initial SR bulking stage.

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Arthur Q. Villordon and Don R. LaBonte

Polymorphism analysis and yield tests were conducted among `Jewel' sweetpotato clones [Ipomoea batatas (L.) Lam] obtained from eight state foundation seed programs. Initially, 38 arbitrary primers generated a total of 110 scorable DNA fragments in a sample of virus-indexed plants from each clone source. The number of marker loci scored for each primer varied from one to eight with an average of 2.89. Twenty-one bands (19.1%) were scored as putative polymorphic markers based on the presence or absence of amplified products. Further estimation of variability within each clone source was accomplished by an assay of 10 sample plants per clone group by 14 marker loci generated by four selected primers. Polymorphic bands ranged from 7.1% to 35.7 % in five of eight clone groups. Field studies show variation in nearly all yield grades measured. In three tests during the 1991 and 1992 seasons, yield differences ranged from 27% to 46% within the economically important U.S. no. 1 root grade. The results suggest the usefulness of arbitrarily-primed markers in detecting intra-clonal sweetpotato DNA polymorphisms and indicate an underlying genetic cause for phenotypic variability in the crop.

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Cecilia E. McGregor and Don R. LaBonte

`White Jewel' is a yellow-and-orange fleshed spontaneous mutant of the orange-flesh sweetpotato [Ipomoea batatas (L.) Lam.] cultivar Jewel. Mutations in storage root flesh color, and other traits are common in sweetpotato. The orange flesh color of sweetpotato is due to β-carotene stored in chromoplasts of root cells. β-carotene is important because of its role in human health. In an effort to elucidate biosynthesis and storage of β-carotene in sweetpotato roots, microarray analysis was used to investigate genes differentially expressed between `White Jewel' and `Jewel' storage roots. β-carotene content calculated from a* color values of `Jewel' and `White Jewel' were 20.66 mg/100 g fresh weight (FW) and 1.68 mg/100 g FW, respectively. Isopentenyl diphosphate isomerase (IPI) was down-regulated in `White Jewel', but farnesyl-diphosphate synthase (FPPS), geranylgeranyl diphosphate synthase (GGPS), and lycopene β-cyclase (LCY-b) were not differentially expressed. Several genes associated with chloroplasts were differentially expressed, indicating probable differences in chromoplast development of `White Jewel' and `Jewel'. Sucrose Synthase was down-regulated in `White Jewel' and fructose and glucose levels in `White Jewel' were lower than in `Jewel' while sucrose levels were higher in `White Jewel'. No differences were observed between dry weight or alcohol insoluble solids of the two cultivars. This study represents the first effort to elucidate β-carotene synthesis and storage in sweetpotato through large-scale gene expression analysis.

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Arthur Q. Villordon and Don R. LaBonte

Genetic uniformity was assessed among sweetpotato (Ipomoea batatas) clones propagated through adventitious and nodal procedures. A single sprout each of `Jewel,' `Sumor,' and L87-95 was used as source of clonal plants that were simultaneously propagated through conventional adventitious procedures and a tissue culture-based nodal culture technique. A sample of 15 decamer primers generated 64 scorable amplified fragments in a PCR-based assay, 29 of which were putatively polymorphic across n = 60 samples (10 each of nodal and adventitiously derived plants/genotype). Within adventitiously derived materials, putative polymorphisms ranged from 4.7% to 31.3% depending on the genotypic class. In contrast, putative polymorphisms ranged from 0.0% to 3.1% among nodally derived samples. Marker loci differentiated genotypes as well as putative marker phenotype variants through a multidimensional scaling analysis of the genetic similarity matrix. An `analysis of molecular variance' shows that genotypic effects accounted for 88.7% of the total molecular marker variability, while propagation effects (within genotypic groups) accounted for 11.3%. Results confirm that clonal plants derived from preexisting meristematic regions are more genetically uniform than plants propagated from adventitious origins.