The Bean Bag

Number 49February 2002

Nodulation and Nitrogen Fixation

(Legume Nodulation Reports not in Allen and Allen 1981)

Joseph H. Kirkbride, Jr.

¹ Status: +, root nodules reported as present; -, root nodules reported as absent.

² Source:

Leguminous Genera of Unknown Response to Rhizobia

Harold D.L. Corby and Joe.H. Kirkbride, Jr.

These lists of leguminous genera whose response to rhizobia is still unknown are presented to encourage their exploration. They are arranged geographically in the following six tables so that Bean Bag Readers may see at a glance the task awaiting them on their doorsteps.

Response has been reported for 493 legume genera comprising more than 17,450 species, leaving 195 genera, comprising some 549 species, still to be explored. One hundred and two genera, 52.6%, are monotypic; 86, 43.9%, have 2-10 species; and six, 3.1%, have 11-20 species. The vast majority is found in tropical areas, and only two genera, Adenopodia C. Presl and Pomaria Cav., occur in both the New and Old Worlds. Pomaria is also the largest genus with approximately 20 species.

The genera, as understood here, are those accepted by the US Department of Agriculture in the Germplasm Resources Information Network [GRIN] (USDA 2001). The tribal classification is that of Polhill (1994a, 1994b), updated to reflect subsequent work (Kirkbride et al. 2000; USDA loc. cit.). The number of species per genus are those of Polhill and Raven (1981), updated to accord with those of Kirkbride et al. (loc. cit.).

Genera are listed by the mid-latitude of their distribution as given in Polhill and Raven (loc. cit.), updated to accord with Kirkbride et al. (loc. cit.). Genera occurring continuously across the equator are listed as equatorial, regardless of their extent on either side of it; those occurring on both sides of the equator, but not across it, are listed by the mid-latitudes of their northern and southern distributions.

Nodule Hunting

For those who may be unfamiliar with nodule hunting, it may be said that by far the best method of search is to raise seedlings in coarse sharp sand, with an admixture of soil from the rhizosphere of flourishing plants of the species concerned. Then, when seedlings are at least two months old, or at flowering if that comes sooner, their roots should be washed clean of soil to reveal any nodules present./p>

Those seeking nodules in the field must, when exploring root-systems too big to be dug out in their entirety, always trace the nodule-bearing roots back to the plant itself - only thus may the nodule be surely related to its supposed parent.

Effective rhizobial nodules (those fixing nitrogen - those being sought) may usually be recognized in being lateral outgrowths of the root with reddish-pink cores. However, these two criteria are not infallible, so specimens of any nodule found should be dried over silica gel for later formal identification; at the same time, specimens of the parent plant should be pressed and dried for the same purpose.

With seemingly non-nodulating species, it is suggested that successive batches of seedlings be raised, using a bacterial inoculum from a different source with each batch, until the tally of flourishing plants without nodules reaches at least 100. And then, and only then, to report that the species has been found to be non-nodulating! Fuller treatment of this subject may be found in Corby (1981, 1988) and Sprent (2001).

Table 1. African genera whose response to rhizobia is unknown and their distribution in Africa.

Ed. Note. Molecular data places Umtiza within subfamily Caesalpinioideae s.l but excludes it from Detarieae s.l.

Table 2. Madagascan genera whose response to rhizobia is unknown.

New World genera whose response to rhizobia is unknown and their distribution in the Americas and Caribbean islands.

Ed .Note. Thylacanthus Tul. , thought to be a monotypic genus from Brazil based on a single collection is Julbernardia paniculata (Benth.) Troupin from Mozambique (Breteler in comm. G.P.Lewis, 1995).

Table 4. Asian and Indo-Pacific island genera whose response to rhizobia is unknown and their distribution in the Asia and the Indo-Pacific islands.

Table 5. Australian genera whose response to rhizobia is unknown and their distribution in Australia.

Table 6. European and Mediterranean genera whose response to rhizobia is unknown and their distribution in Europe and Mediterranean basin.

References

Corby, H.D.L. 1981. The systematic value of leguminous root nodules. In R.M. Polhill and P.H. Raven, eds. Advances in Legume Systematics, Part 2, pp. 657-669. London, Royal Botanic Gardens, Kew.

Corby, H.D.L. 1988. Types of Rhizobial nodules and their distribution among the Leguminosae. Kirkia 13: 53-123.

Kirkbride, J.H., Jr., and Gilbert, L.A. 2001. Legume (Fabaceae) nodulation. USDA Technical Bulletin, in press.

Kirkbride, J.H., Jr., Gunn, C.R., Weitzman, A.L., and Dallwitz, M.J. 2000. Legume (Fabaceae) Fruits and Seeds, CDROM. Boone, North Carolina, Parkway Publishers.

Polhill, R.M. 1994a. Classification of the Leguminosae. In F.A. Bisby, J. Buckingham, and J.B. Harborne, eds., Phytochemical Dictionary of the Leguminosae, pp. xxxv-xlviii. Chapman & Hall, London, Enngland.

Polhill,R.M. 1994b. Complete synopsis of legume genera. In F.A. Bisby, J. Buckingham, and J.B. Harborne, eds., Phytochemical Dictionary of the Leguminosae, pp. xlix-lvii. Chapman & Hall, London, Enngland

Polhill, R.M., and Raven, P.H., eds. 1981. Advances in Legume Systematics, Part 1. London, Royal Botanic Gardens, Kew.

Sprent, J.I. 2001. Nodulation in Legumes. London, Royal Botanic Gardens, Kew.

USDA, ARS, National Genetic Resources Program. 2001. Germplasm Resources Information Network - (GRIN), GRIN Taxonomy. [Online Database] National Germplasm Resources Laboratory, Beltsville, Maryland. Available: http://www.ars-grin.gov/npgs/tax (30 August 2001)