BSc-MSc (Integrated)

Characterization of crop germplasm based on determination of amount and distribution of crop genetic diversity is necessary for proper utilization andconservation. This could be achieved through both morphological and molecular
tools. This study entitled “Genetic diversity analysis of sweet potato (Ipomoea
batatas (L.) Lam.) germplasm using morphological and ISSR markers” was carried
out in the Division of Crop Improvement, ICAR-Central Tuber Crops Research
Institute, Sreekariyam, Thiruvananthapuram during 2017-2018 with an objective to
identify genetic diversity in the sweet potato germplasm based on morphological
and molecular markers.
ICAR-CTCRI is the National Active germplasm site (NAGS) of tropical
tuber crops which maintains 1400 accessions of sweet potato at Sreekariyam and
its regional Centre at Bhubaneswar. 54 accessions of sweet potato including 52
accessions from eastern states of India and two wild species I. triloba and I.
aquatica were selected from this collection.
The study consisted of two parts -morphological and molecular
characterization. Morphological analysis was performed by using eighteen sweet
potato descriptors as provided by IPGRI (CIP et al., 1991). The recorded data was
analyzed statistically by various tools such as PCA and cluster dendrogram using
Multivariate statistical package (MVSP 3.22). The dendrogram separated into the
accessions into two principal clusters and one outlier at a Euclidean distance of 1.2.
The PCA analysis revealed predominant vine colour, leaf lobes type as the major
variables that contributed to the clustering of the sweet potato accessions.
Molecular analysis was performed using ISSR markers. The genomic DNA
was isolated from young leaves using Dellaporta et al. (1983) method. 11 ISSR
primers were used for screening of fifty four accessions. After the final PCR using
selected primers, the product was resolved in 2% agarose and polymorphic bands
were obtained. Primers showed 89.8% polymorphism and the number of bands
ranged from 5 to 16 with a mean value of 7.3 polymorphic bands per primer. A total 63
of 80 polymorphic bands were obtained. The data analysed using NTSYS PC 2.02
program generated a dendrogram, which grouped the accessions based on Jaccard‟s
similarity coefficient which separated the fifty four accessions into three principal
clusters. The first principal cluster comprised of 37 accessions which were grouped
into many subclusters and there was lot of intra-clusteral variation. The second
principal cluster consisted of 15 accessions and this principal cluster comprised of
two accessions with 89% similarity which were also found similar in
morphological characterization. The third principal cluster comprised of the two
wild species, Ipomoea troloba and Ipomoea aquatica. The similarity between the
different accessions ranged between 37-89%. The accessions S1574 and S1576
were 89% similar. The least similar accessions were S1408 and S1572, S1527 and
S1572 (37%). A high diversity of 63% existed within the selected accessions.Mantel‟s test also showed significant correlation (r = 0.0985; p = 0.0003) between
the molecular and morphological distance matrices.
The hexaploid nature of the crop, self-incompatibility, along with the out
crossing nature together might have contributed to the high variation observed
among the accessions.