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Genetic, morphological and cyanogen content evaluation of a new collection of Caribbean Lima bean (Phaseolus lunatus L.) landraces

Maria Montero-Rojas, Morthemer Ortiz, James S. Beaver, Dimuth Siritunga
Genetic resources and crop evolution 2013 v.60 no.8 pp. 2241-2252
microsatellite repeats, seeds, landraces, cyanogen, herbivores, Phaseolus lunatus, agronomic traits, heterozygosity, lima beans, toxicity, genetic variation, hydrogen cyanide, leaves, United States, Haiti, Dominican Republic, Caribbean, Puerto Rico
Lima bean is a species cultivated broadly in the Americas and has been cultivated in the Caribbean for at least 500 years. In order to determine the genetic structure and diversity of Lima bean from the Caribbean, 50 landraces from Haiti, the Dominican Republic and Puerto Rico were collected and analyzed using 24 SSR markers. All landraces in this Caribbean collection were found to be of Middle-American descent. The genetic diversity (HE) was highest in the landraces from Puerto Rico and lowest in Haitian landraces. The observed proportion of heterozygotes (HO) was higher in the Haitian landraces and lowest in Puerto Rican landraces. Unweighted pair-group method with arithmetic averaging analysis showed that the landraces clustered into 3 clusters with all Haitian landraces grouping in one cluster. We also assessed the agro-morphological characteristics of the collection as well as 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 ≤200 ppm 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.