Two Early Nodulation Genes are not Markers for the Capacity of Leguminous Nursery Crops to Form Root Nodules

Abstract

Abstract Little is known about mechanisms that permit or prevent formation of root nodules in which nitrogen gas (N2) is fixed by rhizobial bacteria in association with nursery crops in the legume family. We tested the hypothesis that two genes associated with the fixation of N2 could be used as markers of nodulation capacity among legumes because they occur only in species that can form functional nodules. The presence of ENOD2 and ENOD12 was tested in genomic DNA from three non-nodulating legumes [Cercis canadensis L. (eastern redbud), Gleditsia triacanthos L. var. inermis Willd. (thornless honeylocust), Gymnocladus dioicus (L.) K. Koch (Kentucky coffeetree)] and two nodulating legumes [Albizia julibrissin Durazz. (silk-tree), Laburnum alpinum (Mill.) Bercht. & Presl. (Scotch laburnum)]. Southern analyses indicated that ENOD2 is present in thornless honeylocust, Kentucky coffeetree, and Scotch laburnum, and that ENOD12 is present in eastern redbud, thornless honeylocust, and Scotch laburnum. These results diversify the group of nodulating legumes in which ENOD2 and ENOD12 have been found and show these genes also occur in legumes considered incapable of nodulation. We conclude that neither gene can be used to screen existing or new leguminous nursery crops for the capacity to form N2-fixing nodules.