Genetic diversity analysis of sweet potato (ipomoea batatas (L.) lam.) germplasm using morphological and ISSR markers

Abstract

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.