Nodulation in a Taxonomic Context - Legume Nodulation: A Global Perspective - page 9

Sub-genus Phyllodineae is the only one that has members with both ecto- and ar-
buscular mycorrhizas, a feature that makes them very good for land reclamation and
also for becoming invasive. When Phyllodineae is further subdivided, it may be that
only certain sections have this attribute (Sprent, 1994a). Species can nodulate with a
wide range of rhizobia (Lafay & Burdon, 2001, chapter 4), but Phyllodineae is the only
sub-genus to nodulate effectively with the wide host range strain NGR234 (Pueppke &
Broughton, 1999). Nodulation appears to be a generic characteristic. Leary et al. (2006a)
cite two species that were reported not to nodulate, but these observations have not
been confirmed and probably reflect conditions when samples were collected. Nodula-
tion also appears to be generic for sub-genus Acacia , but not for Aculeiferum , which has
two sections, Aculeiferum, found in Africa and Monacanthea, which is pan-tropical.
So far 16 species of the latter section, from both Africa and America, have been found
unable to nodulate (Sprent, 2001). Proving a negative is always difficult, but these
species have been extensively studied and also form a very close group on molecular
characteristics. It is likely that they have lost the ability to nodulate, rather than never
having had it. The bacteria nodulating sub-genera Acacia and Aculeiferum vary greatly
as does their effectiveness in fixing nitrogen. These aspects will be examined in more
detail in Chapters 2 and 5.
1.2.2 Ingeae
Tribe Ingeae, apart from including at least sub-genus Phyllodineae from the Acacieae,
currently consists of 36 genera, dominated in species by Inga (300) and Calliandra (135)
(Table 1.4). The monospecific genus Faidherbia was for many years called Acacia albida .
Because it is widespread in Africa and has some unusual properties, such as shedding
its leaves in the wet season and producing them in the dry season, it has been the subject
of much research. Most members of Ingeae occur in the New World, but with several
in Africa (including Madagascar), Asia and Australia. Recent evidence suggests that
the Australian and SE Asian genera are closely related (Brown et al., 2008). There are 10
genera (48 spp.) for which there is no information on nodulation status. These include
Viguieranthus , many of whose species were formerly included in Calliandra . Zapoteca ,
on the basis both of a few field observations and of laboratory studies, has not yet been
found to possess nodules. This is the only genus in the tribe with negative reports on
nodulation and more information is urgently needed.
Members of Ingeae are nodulated by a wide range of rhizobia, including some
Burkholderia spp. (Chapter 4). The most widely studied genera for their nitrogen-fixing
properties are Albizia, Calliandra and Inga. Albizia spp. are important shade trees, es-
pecially for cocoa, in large parts of Africa. Calliandra calothysus is widely used in agro-
forestry in Africa, where it is preferred to other woody legumes such as Leucaena
because it seeds less freely and therefore does not become a weed. Although native to
Central America, it nodulates with a range of rhizobia wherever it is grown (Bala &
Giller, 2001). Inga species are also used as nurse and shade crops, the latter often for
coffee in South and Central America. All species have edible fruits and many, for ex-
ample Inga edulis , are grown for this reason. These and many other uses of Inga species
are described in the monograph by Pennington and Fernandez (1998). Inga spp. are
very important in some ecosystems (Chapter 2).