. The host range and specificity is reported of a genetically diverse group
of rhizobia isolated from nodules of Calliandra calothyrsus, Gliricidia se
pium, Leucaena leucocephala and Sesbania sesban.
. Nodule number and nitrogen content was measured in seedlings of herbaceou
s and woody legume species after inoculation with rhizobial strains isolate
d from tropical soils, to establish symbiotic effectiveness groups for rhiz
obial strains and their hosts.
. Specificity for nodulation and N-2 fixation varied greatly among the legu
mes. Symbionts of all four legumes exhibited a wide range of promiscuity an
d symbiotic effectiveness with isolates of S. sesban having the narrowest h
ost range. N-2 fixation varied greatly; although some strains fixed large a
mounts of N-2 with more than one host, none was effective with all hosts. R
hizobial isolates of C, calothyrsus, G, sepium and L, leucocephala were abl
e to effectively cross-nodulate each others' hosts as well as a number of o
ther species.
. The complex nature of cross-nodulation relationships between diverse rhiz
obial strains and legume hosts is highlighted. Host plants inoculated with
effective rhizobial strains showed better nitrogen use efficiency than plan
ts supplied solely with mineral nitrogen.