The interaction between Azospirillum brasilense and Bradyrhizobium japonicum modifies the Bradyrhizobium-soybean symbiosis

TORRES, D; NIEVAS, SOFÍA; LOPEZ, GASTON; CASSAN, FABRICIO; DONADIO, FLORENCIA; MORA, V.

Congreso; XXX REUNION LATINOAMERICANA DE RIZOBIOLOGIA, V CONFERENCIA LATINOAMERICANA DE MICROORGANISMOS PROMOTORES DEL CRECIMIENTO VEGETAL; 2021

In the last four decades, soybean has been extensively inoculated with B. japonicum(biofertilization) as an alternative to chemical fertilization with nitrogen.In South America, B. japonicum is commonly co-inoculated with A. brasilense, amodel free living plant-growth promoting bacteria (PGPR) with the ability toproduce phytohormones and boost legume crop yield in combination with rhizobia.Most inoculants for soybean, wheat and maize in Argentina have B. japonicumE109 (BjE109) and A. brasilenseAz39 (AbAz39) as their active principle.The main aim of our study was to compare and evaluate different strategies forthe combination of BjE109 and AbAz39, and their impact on BjE109-soybeansymbiosis. Five treatments were performed: (1) uninoculated seeds; (2) inoculationwith BjE109; (3) inoculation with AbAz39; (4) co-inoculation with BjE109and AbAz39 (mixed on the seed); and (5) co-inoculation with both strains (mixed24 h before seed treatment). The mix ratio (1:1) and the time of exposure fortreatment 5 were chosen based on preliminary in vitro findings, which showedthat BjE109?s ability to produce exopolysaccharides and degrade auxins was highestunder those specific conditions. For each treatment, we assessed the recoveryof viable rhizobial cells from the inoculated seeds across time, as well as the promotionof symbiosis and plant growth in both glasshouse and field assays. GivingAbAz39 and BjE109 time to interact with each other before their applicationwas found to improve the survival of BjE109 on the seeds. It also increased nodulation,symbiosis and grain yield under field conditions. The changes in the behaviorof B. japonicum seem to be at least partially related to AbAz39?s ability to produceauxins. These results contribute to our understanding of the use of combined biologicalproducts in agriculture.