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

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 (H_E) was highest in the landraces from Puerto Rico and lowest in Haitian landraces. The observed proportion of heterozygotes (H_O) 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.     

Overcoming the barrier to interspecific hybridization of Fagopyrum esculentum with Fagopyrum tataricum

Summary Tartary buckwheat (Fagopyrum tataricum) was successfully hybridized with common buckwheat (F. esculentum), both diploid (2n=16), using the latter as male parent during bud pollination. The barrier normally encountered in such hybridization was overcome by enhancing the cross-compatibility of the two species, which was accomplished by synthesizing a unique genotype of common buckwheat. This novel plant was produced by selecting common buckwheat plants that exhibited, at isozyme loci PGM, SKDH and ADH, alleles with similar mobility to those found in tartary and then transferring these alleles to a single plant through six generations of breeding. Ovule culture was used to rescue the 7–10 day old embryos. On the rescue-culture medium 41% of the hybrid embryos formed calli larger than 200 m in diameter. Most ceased to grow before reaching 1500 m, but four out of 263 cultured ovules continued to grow as callus. One of these differentiated and formed callus with buds and shoots from which cloned plants were produced. The remaining embryos either did not grow at all or formed very small calli. When tartary was crossed with the original genotype of common buckwheat, only 22% of the hybrid embryos formed small calli and none differentiated. Hybridity of the calli and the plantlets was determined by RAPD and isozyme analysis, respectively. Flowers produced by the hybrid plants were of the same type (homomorphic) and size as those of tartary, but with white sepals like common buckwheat.Abbreviations CTAB cetyltrimethylammonium bromide - GA₃ gibberellic acid - IAA indoleacetic acid - IBA indolebutyric acid - PVP polyvinylpyrrolidone     

Retention during processing and bioaccessibility of β-carotene in high β-carotene transgenic cassava root

Cassava is a root crop that serves as a primary caloric source for many African communities despite its low content of β-carotene (βC). Carotenoid content of roots from wild type (WT) and three transgenic lines with high βC were compared after cooking and preparation of nonfermented and fermented flours according to traditional African methods. The various methods of processing all decreased βC content per gram dry weight regardless of genotype. The greatest loss of βC occurred during preparation of gari (dry fermentation followed by roasting) from WT and transgenic lines. The quantities of βC in cooked transgenic cassava root that partitioned into mixed micelles during in vitro digestion and transported into Caco-2 cells were significantly greater than those for identically processed WT root. These results suggest that transgenic high βC cassava will provide individuals with greater quantities of bioaccessible βC.