Abstract
Studies on Rhizobium-legume symbiosis show that trehalose content in nodules under drought stress correlates positively with an increase in plant tolerance to this stress. Fewer reports describe trehalose accumulation in mycorrhiza where, in contrast with rhizobia, there is no flux of carbohydrates from the microsymbiont to the plant. However, the trehalose dynamics in the Mycorrhiza-Rhizobium-Legume tripartite symbiosis is unknown. The present study explores the role of this tripartite symbiosis in the trehalose content of nodules grown under contrasting moisture conditions. Three wild genotypes (P. filiformis, P. acutifolis and P. vulgaris) and two commercial genotypes of Phaseolus vulgaris (Pinto villa and Flor de Mayo) were used. Co-inoculation treatments were conducted with Glomus intraradices and a mixture of seven native rhizobial strains, and trehalose content was determined by GC/MS. The results showed a negative effect of mycorrhizal inoculation on nodule development, as mycorrhized plants showed fewer nodules and lower nodule dry weight compared to plants inoculated only with Rhizobium. Mycorrhizal colonization was also higher in plants inoculated only with Glomus as compared to plants co-inoculated with both microsymbionts. In regard to trehalose, co-inoculation negatively affects its accumulation in the nodules of each genotype tested. However, the correlation analysis showed a significantly positive correlation between mycorrhizal colonization and nodule trehalose content.
Highlights
Common beans represent the most important source of dietary protein in developing countries
It was observed that co-inoculation of Glomus and Rhizobium in bean plants had a negative effect on nodulation parameters (Figs. 1 and 2)
P. filiformis and P. acutifolius showed a low number of nodules, with an average of 12 nodules per plant; under co-inoculation they showed an average of 7 nodules per plant
Summary
Common beans represent the most important source of dietary protein in developing countries. Beans are sown under rainfed systems which expose the plant to variable periods of drought. In this regard, an important effort has been made to produce common bean cultivars tolerant to these challenging conditions. An agronomic practice associated with increased yield in these systems is inoculation with Rhizobium. This type of inoculation improves the nutritional status of nodulated plants, derived from the biological nitrogen fixation (BNF) process, but recently it has been recognized that this inoculation may increase drought or osmotic tolerance of nodulated legumes such as acacia, common bean, lotus, and medicago, through the
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