Diversity and structure assessment of the genetic resources in a germplasm collection from a vanilla breeding programme in Madagascar

A breeding programme of aromatic vanilla, dating back to 1944, was conducted in Ambohitsara, Antalaha, SAVA (Sambava, Antalaha, Vohemara, Andapa) – Madagascar. Imported, local, wild and cultivated vanillas were used as progenitors and thousands of hybrids were generated. However, this germplasm has not undergone any genetic evaluation, and it appears that these valuable genetic resources have been dispersed or lost after the end of the programme (2000). This study aims to investigate the genetic diversity and structure of rescued genotypes currently held in a local collection in Antalaha. Double digest restriction associated-site (RAD)-seq (ddRAD)-seq protocol was applied, providing 865 million read sequences from 56 accessions. The ddRAD sequences have been deposited to the SRA archive of NCBI. From the data, 23,701 filtered concordant common Single Nucleotide Polymorphisms (SNPs) were identified using the three widely used tools (Stacks, BCFtools, Genome Analysis ToolKit - GATK) for short-read library sequencing. These SNPs were used for germplasm evaluation. Clustering analysis segregated samples into five genetic groups: Vanilla planifolia, Vanilla pompona, hybrid Tsitaitra, Vanille Banane and the phenotype Tsivaky. Our analysis revealed distinct subgroups within V. pompona and Tsitaitra, emphasizing the importance of further characterization to accurately reflect the genetic diversity and facilitate better utilization of these accessions in future research and germplasm management. The presence of private alleles in all groups (from 487 to 2866) indicated that populations were diverging and represented a large gene pool that could be useful for future breeding efforts. The genetic data obtained from this study offers valuable insights into the genetic diversity and structure of the vanilla population, with potential applications in breeding and conservation efforts.