The primary objective of this work was to generate species-specific information about root architectural responses to variations in inorganic phosphate (Pi) availability at the onset of storage root formation among six sweetpotato (Ipomoea batatas) cultivars. Three Pi levels were used: 0 (low Pi); 0.17 (medium Pi); and 0.34 (high Pi) g/pot triple super phosphate (0N–46P–0K). The check cultivar ‘Bayou Belle’ (BB) consistently showed evidence of storage root formation at 15 days in adventitious roots (ARs) grown across three Pi levels and two planting dates (PDs). Storage root formation was also detected in ‘Orleans’ (OR) and ‘Beauregard’ (BX), but it was less consistent relative to BB. In general, BB had the lowest adventitious root (AR) number relative to the other cultivars, but the magnitudes of difference varied with Pi availability and PD. With the first PD, BX had a 45% higher AR number compared with BB in low Pi conditions; however, there were no differences in the second PD. Within cultivars, BX and Okinawa grown in low Pi showed combined 17% and 24% reductions in primary root length (PRL) relative to roots grown in high Pi. BB had a higher lateral root number (LRN) and lateral root density (LRD) across Pi levels, corroborating prior data regarding the association of these root architectural attributes with the onset of storage root formation. The experimental data support the hypothesis regarding the existence of genetic variation for Pi efficiency in sweetpotato and that some well-documented Pi-efficient root traits like high LRN and LRD are indirectly selected for in-breeding programs that focus on early storage root formation and stable yields across environments.
Arthur Villordon, Jeffrey C. Gregorie, and Don LaBonte
Don R. LaBonte and David H. Picha
Six sweetpotato cultivars were evaluated for changes in individual sugar concentration, dry weight, and alcohol insoluble solids (AIS) during growth and development. Measurements were taken at weekly intervals from 7 to 21 weeks after transplanting. Sucrose, the major sugar during all stages of development, generally increased in concentration throughout development for `Heart-o-gold', `Travis', and `Jewel', but peaked at 17 weeks for `Beauregard' and `Whitestar'. The high-dry matter white flesh cultivars of `Rojo Blanco' and `Whitestar' contained the lowest sucrose concentration. The monosaccharides glucose and fructose generally decreased in concentration up to 17 weeks in 4 of 6 cultivars, followed by an increase from 17 to 21 weeks in all cultivars. Glucose concentration was marginally greater than fructose at all stages of development in each cultivar. Little or no increase in total sugar concentration occurred during development in `Whitestar' and `Rojo Blanco'. A substantial increase in total sugars occurred during development with `Jewel', `Beauregard', `Heart-o-gold' and `Travis'. Cultivars differed widely in their individual sugar concentrations during development. Percent dry matter increased in all cultivars from 7 to 14 weeks. Dry matter and AIS decreased during the later stages of development.
Arthur Villordon, Jeffrey C. Gregorie, and Don LaBonte
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.
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.
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.
Arthur Q. Villordon and Don R. LaBonte
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.
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.
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.
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.
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.