Agriculture Reference
In-Depth Information
with lenticels, but when older become elongate, but retain the production of lenticels
(H.S. Gehlot, personal communication). One species of
Indigastrum
is pan-tropical and
genera
Phylloxylon
and
Vaughania
plus two species of
Microcharis
are from Madagascar,
with the remaining species of all genera being African.
Abreae and Millettieae
Tribe Abreae has one pantropical genus, with seventeen species, four of which are
known to nodulate. Nodules have been reported as desmodioid and (in other species)
indeterminate, nodulating with slow-growing rhizobia (Sprent, 2001). In view of the
fact that some phaseoloid genera are dimorphic for nodule morphology (see below),
these data are consistent with placement of this genus near tribe Phaseoleae. Tribe
Millettieae is complex, with two major groups being listed in Schrire (2005), with a much
smaller third group (Table 1.14). The latter lacks the inverted repeat of the chloroplast
genome and is included in the IRLC clade. (Fig. 1.5). The two main groups, referred
to as the core and basal groups, span parts of the Phaseoleae. Somewhat depressingly,
just over half the genera have not been examined for nodulation. However, all of those
that have, from all three groups, possess indeterminate nodules, with the infected
region containing both infected and uninfected cells.
Lonchocarpus muehlbergianus
lacks
root hairs and is apparently infected between epidermal cells (Cordeiro et al., 1996).
This feature may be of evolutionary significance (Sprent, 2007) as will be discussed
in Chapter 3. As mentioned earlier,
Dahlstedtia
has primitive nodule structure. Where
known, nodules are usually induced by slow-growing bacteria. In legume phylogenetic
terms, understanding this largely tropical tribe is very important, and it is equally so for
understanding nodule evolution. At present there is no reason on nodulation grounds
to link any of the groups within the tribe to the remainder of the Millettioid clade,
tribes Phaseoleae, Desmodieae and Psoraleae.
The Phaseoloid group; tribes Desmodieae, Phaseoleae and Psoraleae
Apart from some members of the temperate tribe Loteae (see section 1.3.7), tribes
Desmodieae, Phaseoleae and Psoraleae (Table 1.15) are the only ones to have determi-
nate (desmodioid) nodules (Figs. 1.1 and 1.2). There are occasional reports of genera
with dimorphic nodules, for example in
Kennedia
and
Erythrina
. Also, although young
nodules may be desmodioid, occasionally they may become lobed, or even branched
when older (Sprent, 2001) All those tested from these tribes export ureides rather than
amides as the products of nitrogen fixation (Sprent, 2001; Kanu et al., 2008, chapter 5). In
current thinking, tribes Desmodieae and Psoraleae are nested within tribe Phaseoleae
(Schrire, 2005), a fact entirely consistent with nodulation characteristics. However, there
are still many genera that have not been sampled for either molecular or nodulation
characteristics (42 out of 128 for the latter). Unlike many other legume tribes, there are
no confirmed cases of phaseoloid legumes being unable to nodulate.
Two sub-tribes of Phaseoleae, Diocleinae (13 genera) and Ophrestiinae (3 genera),
are separated from the rest of the group on molecular characteristics, being placed close
to the core Millettieae. However, where known, their nodulation characteristics place
them clearly in Phaseoleae (Sprent, 2001; Pueppke & Broughton, 1999). With some
