Selection of Rhizobia from Agronomic Legumes Grown in Semiarid Soils to be Employed as Bioinoculants

Abstract

The aim of this study was to select rhizobia from a collection previously created from nodulated legumes grown in semiarid environments to be used as bioinoculants. The selection was based on the analyses of symbiotic efficiency and molecular analyses. Twenty‐nine strains of rhizobia were evaluated. The symbiotic efficiency was tested by cross‐inoculations with 12 traditional cultivated legumes including pea (Pisum sativum L.), lentil (Lens culinaris Medik.), chickpea (Cicer arietinum L.), vicias (Vicia spp.), clover (Trifolium spp.), alfalfa (Medicago sativa L.), and lupin (Lupinus spp.). The nodC gene was used as a symbiotic marker of host specificity for discriminating and consequently selecting between strains with similar growth values. This rendered 12 symbiotypes which were consistent with their hosts of origin. The 16S‐23S rDNA intergenic spacer region was successfully used for the validation of nodule occupancy revealing its potential for strain identification in nodulation studies. The strains showed variability in their nodulation patterns and the host range was strain‐specific. Some combinations were restrictive displaying nodulation only with their host plants, while it was found that 21 strains of Rhizobium leguminosarum bv. viceae and eight plant species of Fabeae tribe constituted one cross‐inoculation group. Nodule weight, as an indicator of infectiveness, and shoot dry weight, as an indicator of effectiveness, were the plant features employed to discriminate among strains with better symbiotic performance. These molecular and agronomic analyses allowed us to select specific native strains for each plant species and soil of origin. They could be employed in field inoculations trials using cultivars of agricultural legumes previously selected under typical Mediterranean conditions contributing to the development of sustainable agriculture.