BRADYRHIZOBIA ISOLATED FROM FIELD NODULES WITH INCREASED MOTILITY IMPROVE YIELD OF SOYBEAN CROPS

COLLA, DELFINA; PÉREZ GIMÉNEZ, JULIETA; FAURA, ANDRÉS; ITURRALDE, ESTEBAN T.; LODEIRO, A.

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Congreso; Reunión conjunta SAIB-SAMIGE 2020; 2020

SAIB-SAMIGE

Soybean establishes a symbiotic interaction with Bradyrhizobium spp. These bacteria are use as inoculants to improve the yield of soybean crops. However, the efficiency of the inoculants is low due to the problem of competition for nodulation. This problem in mainly due to the occupation of the nodules by field strains. There are several factors that affect the competition for nodulation, such as the distribution of rhizobia in the soil or the motility of the rhizobia. Previous work showed that rhizobia that have more motility increase the yield of soybean crops in the field. Our group has a collection of rhizobia isolates from nodules and soil that are capable of nodulating soybean. We selected those that have a good efficiency in Biological Nitrogen Fixation (BNF) and were good competitors for nodulation. These strains were identified by sequencing 16SrRNA and housekeeping genes (atpD, recA and glnII). Afterwards, phylogenetic analyzes were performed. One of them, B. japonicum CAS/N-10, was selected to obtain a derivative with an increase mobility. We used an artificial selection method that has been developed in our laboratory which allowed us to obtain a strain with higher mobility (CAS/N-10 m+). This strain has the same growth kinetics as the wild type and symbiotic properties. Furthermore, when CAS/N-10 m+ strain is isolated from nodules, it maintains the higher motility phenotype. Field trials were carried out to calculate the yield when the soybean plots were inoculated with the motility-improved strain and the parental strain. The experiments were carried out in Pergamino (Buenos Aires province), Rufino (Santa Fe province) and Monte Buey (Córdoba province) during the 2019/2020 soybean season. Field trials demonstrated that the plots inoculated with CAS/N-10 m+ had a higher yield than those that were inoculated with the wild type strain. In order to promote a better distribution of rhizobia in soils and to improve the competition for nodulation of the strains used as inoculants, an easy artificial selection method was used to obtain a strain with increased motility. In this way, using this approach over field-isolated strains that already have a good symbiotic performance, improve yields on soybean crops are obtained.