Morphological and Taxonomic Diversity of Taxa Considered as Infrataxons of Phaseolus lunatus L. in Benin

Aims: Parataxonomic work on Lima beans has shown that this plant is subject to taxonomic confusion. The objective of this study is to clarify the taxonomic position of plants grown in Benin as local varieties of Phaseolus lunatus L.

Methods: Thus an experimental field of 99 accessions, from the 33 local varieties of P. lunatus recorded in Benin, was installed. Quantitative and qualitative data were collected from seedling emergence to fruit ripening.

Results: A total of 07 species were identified among the taxa considered as local varieties of P. lunatus by the 990 farmers surveyed. Of these, 77.58% actually recognized the species but 22.42% cultivated other species that they mistakenly assimilate to local varieties of P. lunatus. The latter are mostly dominated by farmers in the Sudanian zone. The seven (07) species identified are: Phaseolus lunatus, Sphenostylis stenocarpa (A.Rich.) Harms, Mucuna pruriens (L.) DC. var. utilis (Wall. ex Wight) Baker ex Burck, Canavalia africana Dunn, Canavalia ensiformis (L.) DC., Canavalia gladiata (Jacq.) DC. and Canavalia sp. Of the 33 taxa and 99 accessions followed, 25 taxa and 75 accessions are for Phaseolus lunatus. Within the 75 accessions of P. lunatus, six (06) qualitative morphological characters of which five (05) seed-related showed significant variability (seed coat pattern, seed coat colour, hilum belt colour, seed shape and size). These traits enabled nine (09) morphotypes to be distinguished.

Conclusion: The present work has thus shown the importance of morphological traits related to the seed in the discrimination of morphotypes as was the case in the vernacular nomenclature of the species. They are therefore potential indicators in genetic improvement programmes. However, knowledge of their degree of heredity requires molecular genetic analyses.