Identification des rhizobiums indigènes piégés à partir de la légumineuse Pisum sativum L. en Algérie, par approche polyphasique.

Abstract

The legume family is economically important for food production and soil fertility. Many legumes have the ability to establish a symbiosis with soil bacteria called rhizobia. This interaction leads to the formation of a new root or in a few cases stem organ, the nodule, within which the bacteria can fix atmospheric nitrogen. This study aims to characterize phenotypically and genotypically the symbiotic bacteria nodulating the legume Pisum sativum L. The rhizobial strains living in the rhizosphere of forage pea were trapped in vitro from the collected soils. The study included seven sites located in Eastern and Central Algeria representing two agro-climatic zones, sub-humid and semi-arid. A collection of 94 isolates was obtained by direct isolation, or by bacterial trapping. 34 of them are rhizobial strains capable, with two exceptions, of establishing symbiosis with two cultivars of the forage pea (P. sativum cv. Sefrou and P. sativum cv. Trapper). Characterization using morphological tests, urea hydrolysis, nitrate reduction, cellulolytic and pectinolytic activity as well as growth at different temperatures gave a description comparable to that of Rhizobium. Different profiles of susceptibility to rhizobiophages indicated that the majority of isolates were likely to be members of the R. leguminosarum group of species. It is interesting to note that two isolates were resistant to all rhizobiophages. The strains revealed various plasmid profiles using Eckardt gels. 19 restriction profiles were distinguished based on PCR-RFLP of the cpn60 gene, and 15 distinct hybridization profiles were obtained using Southern blot analysis of nodABC genes. The 16S rRNA gene sequences showed that all isolates exhibited 99.85 % similarity to R. leguminosarum sv. viciae USDA 2370T, R. laguerreae FB206T and R. anhuiense CCBAU 23252T. Analysis of the cpn60 sequences revealed two groups. One of them was clustered with ≤ 99 % identity with R. laguerreae FB403. The second was clustered with ≤ 99 % identity with R. laguerreae FB206T. Our results suggest that the isolates may belong to the species R. laguerreae.