Molecular identification, genetic diversity, and secondary structure predictions of Physalis species using ITS2 DNA barcoding.

Background: The genus Physalis belongs to the Solanaceae family and has different species with important nutritional and medicinal values. Species within this genus have limited morphological differences, a characteristic that hinders accurate identification, safe utilization and genetic conservation of promising genotypes. In addition, to prevent the perceived loss of Physalis diversity due to habitat destruction, species delimitation needs attention. In this study, we used the sequence and structural information of the internal transcribed spacer 2 (ITS2) barcode to efficiently identify and discriminate Physalis species from a collection of 34 Physalis accessions.

Methodology: Physalis plant samples were collected from eight Counties in Kenya based on the availability of the germplasm. The voucher specimens were identified using the botanical taxonomy method and were deposited in the University of Nairobi herbarium. A total of 34 Physalis accessions were identified and accessed for diversity based on the ITS2 barcode region. The sequence similarity of the ITS2 genes was analyzed through the Basic Local Alignment Search Tool (BLAST), the nearest Kimura-2-parameter (K2P) genetic distances were calculated and a phylogenetic tree was constructed using the Bayesian inference (BI) method in MrBayes 3.2.7a software. The differences in the ITS2 secondary structure between the species were analyzed.

Results: The success rate of PCR amplification and sequencing was 75% and 67%, respectively. The analyzed ITS2 sequences displayed significant inter-specific divergences, clear DNA barcoding gaps and high species identification efficiency. Based on the constructed phylogenetic tree, three Physalis species (Physalis peruviana, Physalis purpurea and Physalis cordata) were identified and were clustered in a homogenized distribution. High genetic diversity (0.36923) and genetic distance (0.703) were observed between Physalis peruviana and Physalis cordata. The highest genetic nucleotide diversity (0.26324) and distance (0.46) within species was obtained for Physalis peruviana. The differences in the secondary structures generated from this study discriminated between the Physalis species.

Conclusions: Our study demonstrated that ITS2 is a potential DNA barcode for effective identification and discrimination of Physalis species. The results of this study provide insights into the scientific basis of species identification, safe utilization, genetic conservation and future breeding strategies for this important nutritional and medicinal plant species.