RESUMEN
Root-knot nematodes, genus Meloidogyne, are the most damaging nematodes of sweetpotato causing yield reduction and aesthetic damage of the marketable product. Several sweetpotato cultivars currently grown in the United States have intermediate to high resistance to Meloidogyne incognita, however, many of these cultivars are susceptible to M. enterolobii. Therefore, the response of 69 sweetpotato genotypes to M. enterolobii and M. incognita was evaluated under greenhouse conditions to identify potential sources of resistance. The cultivars 'Beauregard' and 'Jewel' were used as controls. Results showed that sweetpotato genotypes were either highly resistant or highly susceptible to M. enterolobii, while they showed a wide spectrum response to M. incognita ranging from highly susceptible to highly resistant. Twenty-six genotypes were resistant to M. enterolobii and eleven genotypes were resistant to M. incognita. Combined resistance to M. enterolobii and M. incognita was observed in three sweetpotato genotypes. Selected genotypes from this study will be used to incorporate the observed resistance into a commercially viable sweetpotato cultivar.
RESUMEN
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.
