Siderophore cross-utilization amongst nodule isolates of the cowpea miscellany group and its effect on plant growth in the presence of antagonistic organisms

Nodule isolates from the cowpea miscellany group of legumes produced varying concentrations of catecholate and hydroxamate types of siderophores under iron-limiting conditions. The nodule isolates differed with respect to siderophore cross-utilizing abilities; some were proficient at using siderophores of other nodule isolates (homologous siderophores) while others could utilize siderophores produced by other rhizospheric bacteria (heterologous siderophores). Utilization of siderophore of rhizospheric bacterium PsB, a plant pathogen, benefited the nodule isolate G11 in terms of growth under iron-limiting laboratory conditions, while PsB was clearly inhibited in the presence of G11. Plate assays showed that siderophore of G11 could withhold iron from PsB and hence PsB was inhibited in the presence of G11. Isolates G11 and PsB when applied simultaneously to peanut seedlings under sterile soil conditions, provided a clear advantage to the plant in terms of reduction in the inhibitory effect of PsB. The count of the nodule isolate G11 increased in the soil when co-inoculated with PsB, as compared to when inoculated alone. Thus, the increased growth of the plant can be attributed to the iron sequestration and plant growth promoting properties of G11. The isolate G11 could utilize the siderophores produced by many other rhizospheric isolates while the siderophore of G11 was not being utilized by these rhizospheric isolates.