Don R. La Bonte

Studies on Beauregard sweetpotato clones naturally infected with viruses

The response of clonal sweetpotato naturally infected with viruses was investigated. Analyses included yield, canopy biomass, and root colour on twelve virus infected (V + ) clones and corresponding virus-tested (V−) mericlones (clones derived from meristem-tip culture) of ‘Beauregard’ sweetpotato. All V + clones tested positive for Sweet potato feathery mottle virus and some clones additionally tested positive for Sweet potato virus G (SPVG) and/or the newly identified Ipomoea vein mosaic virus (IVMV). The V− mericlones had greater marketable yields for the important US No. 1 grade in three of four plantings in comparison to their V + clonal counterparts. Comparisons within V− mericlones did not show significant yield differences, suggesting clonal variation was minimal in this randomly selected set of ‘Beauregard’ mericlones. Canopy vine weight was lower overall in two of three plantings for V + clonal variants in comparison to their V− mericlones. Skin and flesh was redder and more yellow in V− mericlones in comparison to their V + clonal counterparts, cumulatively resulting in a deeper orange tissue. Our results from mericlone comparisons suggest that clonal variation was minor on general agronomic traits of ‘Beauregard’ sweetpotato and that variation in yield, canopy, and root coloration among V + clones and V− mericlones was mostly a function of virus infection.

Transcriptome Profiling of Beach Morning Glory (Ipomoea imperati) under Salinity and Its Comparative Analysis with Sweetpotato.

The response and adaption to salt remains poorly understood for beach morning glory [Ipomoea imperati (Vahl) Griseb], one of a few relatives of sweetpotato, known to thrive under salty and extreme drought conditions. In order to understand the genetic mechanisms underlying salt tolerance of a Convolvulaceae member, a genome-wide transcriptome study was carried out in beach morning glory by 454 pyrosequencing. A total of 286,584 filtered reads from both salt stressed and unstressed (control) root and shoot tissues were assembled into 95,790 unigenes with an average length of 667 base pairs (bp) and N50 of 706 bp. Putative differentially expressed genes (DEGs) were identified as transcripts overrepresented under salt stressed tissues compared to the control, and were placed into metabolic pathways. Most of these DEGs were involved in stress response, membrane transport, signal transduction, transcription activity and other cellular and molecular processes. We further analyzed the gene expression of 14 candidate genes of interest for salt tolerance through quantitative reverse transcription PCR (qRT-PCR) and confirmed their differential expression under salt stress in both beach morning glory and sweetpotato. The results comparing transcripts of I. imperati against the transcriptome of other Ipomoea species, including sweetpotato are also presented in this study. In addition, 6,233 SSR markers were identified, and an in silico analysis predicted that 434 primer pairs out of 4,897 target an identifiable homologous sequence in other Ipomoea transcriptomes, including sweetpotato. The data generated in this study will help in understanding the basics of salt tolerance of beach morning glory and the SSR resources generated will be useful for comparative genomics studies and further enhance the path to the marker-assisted breeding of sweetpotato for salt tolerance.

Studies on sweetpotato with chlorotic leaf distortion, caused by Fusarium lateritium

Abstract The response of sweetpotato to inoculation with the chlorotic leaf distortion (CLD) pathogen, Fusarium lateritium was investigated. Analyses included vine growth, canopy biomass, chlorophyll concentration, net photosynthetic rate and yield on CLD affected (CLD+) and CLD free (CLD‐) mericlones (clones derived from meristiem‐tip culture) of sweetpotato genotypes. Gentotype L82–527, showed delayed vine growth but overcame the delay in one of two sequential plantings while NC‐845, L85–237, L86–33, ‘Porto Rico’, ‘Jewel’ and ‘Beauregard’ were unaffected. Chlorotic, newly opened leaves on CLD+ plants had lower chlorophyll a and b concentrations and lower net photosynthetic rates. However, no reductions in net photosynthesis were observed when mature CLD+ leaves were measured; a few genotypes had lower chlorophyll content. Chlorotic leaf distortion did not lower marketable yields in any genotype. Our results suggest that only young foliage is adversely affected by CLD and that the photosynthetic potentia...