Molecular phylogeny and genetic diversity of sweetpotato (Ipomoea batatas) and its wild relatives
MOLECULAR PHYLOGENY AND GENETIC DIVERSITY OF SWEETPOT A TO (Ipomoea hatatas) AND ITS WILD RELATIVES
for the degree of Doctor of Philosophy at The University of Hong Kong
in May 2000
Sweetpotato, Ipomoea halalas, is an important food crop grown in more than 100 countries. How the crop evolved has not been fully resolved. In this thesis, genetic diversity and relationships of sweetpotato and its wild relatives were examined using inter-simple sequence repeats (ISSRs), restriction-site variation of chloroplast DNA (cpDNA PCR-RFLPs), amplified fragment length polymorphism (AFLPs), and the internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA sequences.
A total of 2,071 ISSR fragments were generated with 15 primers in a sample of 40 accessions, including sweetpotato and nine of its wild relatives in the series Ipomoea ser. Balalas. The ISSR fragments were highly polymorphic (62.2%). Restriction analysis of four noncoding regions of cpDNA revealed 47 informative restriction-site and length mutations in the 40 accessions. Out of the 40 accessions, highly informative fingerprints were generated for 36 accessions using AFLP markers. A total of 891 parsimony informative AFLP characters were generated with six pairs of primers. Phylogenetic analysis of ISSR, cpDNA and AFLP datasets revealed generally similar relationships at the interspecific level, but the high levels of polymorphism of AFLPs and ISSRs resulted in a better separation of intraspecific accessions. Of the nine wild species examined, I lrifida was found to be the most closely related to cultivated sweetpotato (the hexaploid I halalas), while 1. ramosissima and I umbralicola were the most distantly related to I balalas within the series. Three species, 1. leucanlha, I cordalortriloba and L grandifolia were closely related to one another. Ipomoea tri/oba, hitherto considered to be one of the
ancestors of 1. halalas, was closely related to 1. cynachifolia, but only distantly related to 1. batatas based on ISSR and AFLP data.
ITS sequences of all species except 1. littoralis, in the series Batatas, plus five outgroup species, were determined. A 28 bp deletion was found in ITS 1 in all ingroup species except 1. umbraticola. Sequence divergence of ITS was low among species in the series. ITS sequences lack sufficient variation to elucidate all the relationships among the species in 1. series Batatas, but they did support the present circumscription of the series Batatas.
The second part of this thesis was to study genetic diversity of germplasm collections of sweetpotato from the Asia and Pacific region. Using AFLP markers, a high level of genetic diversity was found in the sweetpotato gene pool. In contrast to their ancestors in America, the cultivars from Asia showed no geographical patterns in their relationships. Repeated introductions may have resulted in the lack of geographical grouping among accessions. Low rates of redundant accessions were found in the germplasm sampled. Accessions from the Solomon Islands, Japan, New Zealand, Tonga, Philippines and Indonesia exhibited higher levels of diversity than those from Taiwan, Korea and Papua New Guinea.
The molecular markers used in this study proved to be efficient for the phylogenetic reconstruction of sweetpotato and its wild relatives. The information obtained in the present study may be valuable in revealing the origin ofthe cultivated sweetpotato and in sweetpotato breeding programs.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:sweet potatoes genetics
Date of Publication:01/01/2000