BSc-MSc (Integrated)

The study entitled “Identification of duplicates in the germplasm of sweet potato (Ipomoea batatas (L.) Lam.) using morphological and molecular markers” was carried out at the Division of Crop Improvement, ICAR-Central Tuber Crops Research Institute, Sreekariyam, Thiruvananthapuram during 2016-2017. The objective of the study was to identify duplicates in the sweet potato germplasm based on morphological and molecular markers. Identification and elimination of these common redundant materials will enhance the germplasm viability.
Fifty accessions were selected for the study. The study was divided into two phases - morphological and molecular analysis. Morphological analysis was performed by using twenty descriptors as provided by IPGRI (CIP et. al., 1991). The recorded data were analyzed statistically by various tools such as PCA and cluster dendrogram. Cluster dendrogram identified three sets of morphological duplicates and the accessions were separated into six principal clusters and two outliers at a Euclidean distance of 1. The PCA analysis revealed predominant vine colour and secondary vine colour, abaxial vein pigmentation and petiole pigmentation as the major factors that contributed to the clustering of the sweet potato accessions.
After morphological analysis, molecular analysis was performed. The genomic DNA was isolated using CTAB method which gave good quality DNA. 11 ISSR primers were used for screening of fifty accessions. After the final PCR using selected primers, the product was resolved in 2% agarose and polymorphic bands were obtained. All the primers showed 100% polymorphism and the number of bands ranged from 9 to 18 with a mean value of 14.7 bands per primer. Using the molecular scoring data, UPGMA clustering was done and the whole fifty accessions were divided mainly into two principal clusters and one outlier. The first principal cluster comprised of 40 accessions which were grouped into many subclusters and there was lot of intraclusteral variation. The second principal cluster consisted of 9 accessions and this principal cluster comprised of two true duplicates which were also found similar in morphological characterization. The outlier was different from all the other accessions and may be due to the peculiar leaf shape which is not seen in other accessions selected in the study. SD-29 was different from all the remaining accessions by a similarity coefficient of 0.61.The similarity between the different accessions ranged between 52-100%. The duplicates S-236 and S-256 were 100% similar. The least similar accessions were SD-39 and S-298 (52%). Thus it can be inferred that a 48% variability or diversity existed within the selected accessions which can be considered as a moderate diversity.
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. Only two duplicates were identified. In future more specific markers may be used for core collection development and to eliminate duplicates.