Molecular differentiation and diversity of cassava (Manihot esculenta) taken from 162 locations across Puerto Rico and assessed with microsatellite markers

Abstract

Background and aims Knowledge of germplasm diversity and its genetic characterization is an invaluable asset in crop improvement as well as conservation strategies. Although an important crop and present in the Caribbean since the 15th century, the origins of today’s cassava in the Caribbean are poorly understood. Genetic variability and long growing cycles provide a unique set of challenges when researching cassava, and it is in part due to these challenges that little knowledge regarding the genetic diversity of cassava in Puerto Rico exists. Methodology In order to evaluate the genetic diversity of cassava in Puerto Rico, 162 samples with unknown genetic background were collected from different townships of the island and were analysed by 33 single sequence repeat markers. For comparative purposes, 23 accessions of the Puerto Rican cassava germplasm collection were also evaluated. Principal results Our results show that the genetic diversity (HE) of unknown cassava samples (0.7174) is slightly higher than in the current Puerto Rican cassava collection (0.6996). The observed proportion of heterozygotes (HO) was higher in the Puerto Rican cassava collection compared with the unknown samples. An unweighted pair-group method with arithmetic averaging analysis showed that most of the samples clustered with the accessions of the Puerto Rican cassava collection. However, there was one cluster of only unknown cassava samples and no accessions of the Puerto Rican collection. Members of this cluster most likely share alleles which are not represented by the accessions in the collection. Conclusion This broad study shows the presence of high levels of genetic diversity in the unknown samples. Traditional practices, especially intercropping and incorporation of volunteer seedlings, have led to the contribution of recombinant genotypes to cultivated stocks. This study revealed a high potential for local Puerto Rican cassava to be a useful part of future genetic improvement programmes.