The tribe Phaseoleae (family Leguminosae) is home to many of the annual food
legumes cultivated in the tropics. Cowpea
(Vigna unguiculata (L.) Walp.), Bambara groundnut
(Vigna subterranea (L.) Verdc.), Kersting’s bean
(Macrotyloma geocarpum L.), mung bean
(Vigna radiata (L.) Wilczek) and common bean
(Phaseolus vulgaris L.), all belonging to subtribe
Phaseolinae, and together with soybean (Glycine max (L.)
Merr., subtribe Glycininae) and pigeon pea
(Cajanus cajan L., subtribe Cajaninae), are important
members of the tribe Phaseoleae. These legumes are unique in their use of
identical root chemical molecules to induce the expression of nodulation genes
in their respective homologous microsymbionts during nodule formation. Of
those studied so far, common bean, soybean, Bambara groundnut,
Kersting’s bean and cowpea all use the isoflavones daidzein, genistein
and coumestrol as root exudate signals to induce the expression of
nod genes in their rhizobial partners. Additionally,
members of the Phaseoleae tribe are easily recognised on the basis of their
tropical biogeographic origin, broad host nodulation habit, route of
Rhizobium entry into roots, chemotaxonomy and use of a
common isoflavone biosynthetic pathway, determinate nodulation phenotype and
internal nodule anatomy, xylem composition and transportable solutes of fixed
N, site of NO3– reduction
and metabolic response of N2-fed plants to
NO3– supply. These shared
traits and their potential application for agriculture are discussed in this
review.
Nitrate inhibition of N2 fixation and its effect on micronutrient accumulation in shoots of soybean (Glycine max L. Merr.), Bambara groundnut (Vigna subterranea L. Vedc) and Kersting’s groundnut (Macrotyloma geocarpum Harms.)
