Genetic and Cyanogen Content Evaluation of a New Collection of Caribbean Lima Bean (Phaseolus lunatus L.) Landraces.

Crop diversity in part is maintained by farmers who share plant material, introduce new varieties and even select improved genotypes. Also the farmers keep and, in some cases without knowing, protect the wild relatives of many different species. The establishment of genetic relations within a crop is an important component in crop improvement programs. In this study, we report the genetic diversity assessment of lima beans (Phaseolus lunatus L.) in the Caribbean. Lima bean is a drought and heat tolerant grain legume crop that is produced and consumed throughout the Caribbean. Fifty landraces collected from the PR, Haiti and DR were subjected to 24 fluorescence-based Simple Sequence Repeat marker analysis on polyacrylamide gels. All landraces in this Caribbean collection were found to be of Middle-American descent. The genetic diversity was highest in the landraces from Puerto Rico and lowest in Haitian landraces. UPGMA analysis showed that the landraces clustered into 3 clusters with all Haitian landraces grouping in one cluster. We also assessed the content of cyanogenic glucoside, linamarin, in leaves and dry seeds. Lima bean, which is a model crop for indirect plant defenses against herbivory, also possess linamarin as a source of direct plant defense. Upon tissue damage, linamarin is converted to toxic hydrogen cyanide. In our collection 44.6% of the landraces had average seed HCN content ≤200ppm which is the permitted level for Lima bean seed in the US. Our results also identified the landraces in this collection which have high linamarin levels in the leaves while having low levels in the seeds. Such landraces have the desirable combination of traits and will be the focus of our future plans for agronomic trait improvement though breeding.