Agriculture Reference
In-Depth Information
Tab l e 1 . 2
Generic changes that have unwittingly included nodulation. Nodulating genera in bold
type. They include one genus from each sub-family
Old genus
New genera
Reference
Cassia
Cassia, Senna,
Chamaecrista
Irwin & Barneby, 1982
Newtonia
Newtonia,
Pseudopiptadenia
Lewis & Lima, 1991
Sophora
Sophora,
Styphnolobium
Sousa & Rudd, 1993
tribes, but which also occurs in some others, causing some difficulties for classification,
discussed later. As each of these two changes is thought to have occurred only once, it
is hoped that when more genera have been analysed for them, their presence/absence
will help clarify some anomalies. Although very important for legume phylogeny,
there are no known nodulation characteristics involved in these chloroplast genome
changes (or, indeed, in the chloroplast genome at all).
In the following sections, brief reference will be made to nodule morphology and
structure (Figs. 1.1 and 1.2), and to the bacteria inducing nodules, detailed in Chapter
4. Basically, bacteria nodulating legumes are known collectively as rhizobia, and they
fall within several families of two branches (
) of phylum Proteobacteria. Earlier
they were often categorised in terms of fast or slow growth and these terms will also
be used here.
and
1.1 Caesalpinioideae
This sub-family has long been known to contain the smallest proportion of nodulated
species (Allen & Allen, 1981). However, it is worth re-examining the distribution of
nodulation in the light of currently described tribes. Cercideae and Detarieae are basally
branched from the rest of Caesalpinioideae (Fig. 1.3): neither has known nodulated
members and Detarieae is uniformly ectomycorrhizal. Most legumes are arbuscular
mycorrhizal (AM) or, in some cases, have both types. Tribe Cassieae has one nodulat-
ing genus,
Chamaecrista
. However, this has 330 species, a significant number of which
have been recorded as nodulated and none as non-nodulated. This genus represents
nearly half the species in the tribe. Further, sub-tribe Cassiinae, which contains
Chamae-
crista
, appears to fall within the confines of tribe Caesalpinieae (Lewis, 2005a; Fig. 1.3),
which contains all other known nodulating genera. Caesalpinieae has been divided
into a number of groups, some of which contain only non-nodulating genera. Nodu-
lated genera are scattered among several groups, with no apparent logic. In a more
recent study, Bruneau et al. (2008) sampled all but one of the caesalpinioid genera,
but with varying levels of rigour because of the availability and quality of DNA. This
analysis clarified the relations among many of the genera. Unfortunately the nodulated
genera remain scattered and the hope expressed by Haston et al. (2005) that, with the
inclusion of more molecular characteristics, the nodulating genera may emerge as more
closely related than generally thought has not yet been fulfilled. One generic change
