Cowpea [Vigna unguiculata (L.) Walp.] maternal lineages, chloroplast captures, and wild cowpea evolution

Abstract

Vigna unguiculata is the major grain legume in Africa and is also important in South-East Asia as a vegetable. The wild relatives, present only in Africa, are currently made of ten subspecies. However, while the different groups are well identified, the relationships between them are not firmly established. The present study of chloroplast diversity through restriction fragment length polymorphism confirms the different groups, as well as the split between savannah subspecies and forest subspecies. It justifies treating subsp. stenophylla as a subspecies independent from subsp. protracta and invalidates the subsp. stenophylla sensu lato concept. It suggests that the species V. unguiculata originated in southern Africa and that the annual subsp. unguiculata var. spontanea originated in eastern Africa. More importantly, it proves that three subspecies are of hybrid origin, between the annual var. spontanea and various perennial subspecies from southern Africa with left-twisted keel. Owing to its annual and inbred properties, var. spontanea spread across all African low-to medium-altitude savannahs, displacing the lefttwisted keel savannah perennials from their warmer and drier areas.

Revisiting the Domestication Process of African Vigna Species (Fabaceae): Background, Perspectives and Challenges

“…Pasquet., also known as subsp. dekindtiana sensu Verdcourt non Harms [69][70][71][72][73][74][75][76]. Besides the domesticated cowpea, the dekindtiana group includes some obligate short-day wild forms, well adapted to arid environments.…”

“…While the var. spontanea grows especially around cultivated fields and roadsides, and it is recognized as the progenitor of domesticated cowpea [75,[77][78][79], the subspecies alba, pubescens, tenuis, stenophylla and dekindtiana are perennial plants [75,76]. The development of new molecular tools to discriminate among wild, weedy, and cultivated accessions is considered a modern and fundamental target, particularly needed for disentangling the complex taxonomic relationships among subspecies and to discriminate between true wild plants and ferals.…”

“…tenuis, stenophylla and dekindtiana are perennial plants [75,76]. The development of ne molecular tools to discriminate among wild, weedy, and cultivated accessions is consi ered a modern and fundamental target, particularly needed for disentangling the comple taxonomic relationships among subspecies and to discriminate between true wild plan and ferals.…”

“…Molecular analysis using AFLP [74] and internal transcribed spacers [53,169,170] have confirmed the natural propensity to hybridisation between subspecies and have revealed intricate intraspecies phylogenetic relationships. Intragenomic 5S rRNA repeat unit heterogeneity was interpreted as the consequence of extensive hybridisation events [170], and recently, plastid DNA sequences have confirmed chloroplast capture events [76].…”

“…spontanea [216]. The distinction between feral and truly wild lineages is ever more complicated because introgression produces fertile offspring and the small seed-size typical of wild forms is dominant to large seed size [76,217]. Moreover, var.…”