Cowpea is an important food grain legume in the Sudano Sahelian zone of Mali. So far, an attention
has not been addressed to the diversity of bradyrhizobia nodulating cowpea in this area. In order to
fill this gap, effects of 3 cowpea varieties (IT89KD-374, CZ1-94-23-1 and CZ11-94-5C) on the diversity
of native bradyrhizobia has been studied in 3 cropping systems from 2007 to 2008 at Cinzana
Agronomic Research Station. The objective of the study was to identify effective bradyrhizobia
strains nodulating cowpea and their impact on the intercropped or subsequent millet yield in the
main cropping systems. Experimental design was a Randomized Complete Block Design using a
factorial combination of 3 cowpea varieties and 3 cropping systems in 4 replications. PCR-RFLP and
sequencing of the 16S – 23S of rDNA IGS were used to identify bradyrhizobia strains associated with
cowpea varieties. Six IGS types have been identified. IGS type I (strain Bradyrhizobium sp.ORS 3642)
was the most competitive regardless of cropping system and cowpea variety. The greater diversity
averaged bradyrhizobia was found in variety IT89KD-374 (H' means = 0.39). Best millet grain yield in
intercropped system (1520 kg ha-1) was obtained with cowpea variety IT89KD-374. The best above
ground dry biomass production of subsequent millet (6 210 kg ha-1) has been obtained under CZ11-
94-5C – millet rotation. Types IGS IV and VI (ORS 3637 and STM 3378 strains respectively) appeared
to be responsible for the performance of the Cowpea-millet rotation and cowpea variety CZ11-94-5C.