Biochemical and physiological characterizations of Rhizobium-Pea (Pisum sativum L.) symbiotic association under abiotic constraints.

Abstract

Pea (Pisum sativum L.) is an important leguminous for the agricultural sector. It is a source of biological nitrogen that efficiently contributes to the soil fertility. In Tunisia, low pea production is due to bad nitrogen management, lack of phosphorus availability and to the abiotic constraints. Thus, in order to improve the pea production ,a new farming technique involving the rhizobia inoculation was applied. The symbiotic, biochemical, physiological characterization and inoculation trials were performed in both the laboratory, greenhouse and open field. Pea Lincoln variety was used as legume species and fifteen Rhizobium strains isolated from the roots of the nodulated pea were collected from different Tunisian areas. Several physiological and biochemical parameters, i.e. pH, temperature, calcium carbonate and salinity were assessed to characterize the strains nodulating pea. All the rhizobia tests were evaluated on Yeast Extract Mannitol Agar medium (YEMA). Pea nodulation and Gallery API test were carried out under controlled conditions. Significant differences (p<0.01) between the nodules number induced by the different bacterial strains and between strains for the dry matter quantities of aerial and root parts were registered. The pH medium test results showed that among 15 strains only 8 strains having a halo diameter greater than 1 cm at basic pH. The most of isolates are able to grow at both low and high temperatures. The limestone test results qualify these rhizobia as calcifuges. Gallery API test results showed a great diversity of rhizobia assimilation of carbohydrates implying genetic diversity. Our results us to select the most efficient solubilizer Rhizobium strains nodulating pea. In order to confirm the previously cited notions on the diversity of Rhizobium strains isolated from Pisum sativum roots in Tunisia, inoculation trial with both selected strains in controlled and open field conditions confirmed the capacity of selected strains to fix atmospheric nitrogen and promote plant growth.