Banca de DEFESA: FABÍOLA KELLY NASCIMENTO DOS SANTOS

Performance of chemically induced mutants of Gluconacetobacter diazotrophicus strain PAL5 and Azospirillum baldaniorum strain Sp245 in promoting the growth of upland rice plants

Upland rice; Plant-bacteria interactions; diazotrophic bacteria

The excretion of ammonium and the overproduction of auxin are unique functional characteristics that are not frequently observed in diazotrophic bacteria associated with agriculturally important plants. These properties allow such bacteria to eventually enhance the plant growth-promoting effect. For this reason, the present study aimed to characterize mutant strains of Gluconacetobacter diazotrophicus strain PAL5 and Azospirillum baldaniorum strain Sp245 regarding ammonium excretion and the production of indolic compounds, as well as to evaluate their plant growth-promoting potential in rice plants (Oryza sativa cv. BRS Esmeralda). A total of 25 strains, deposited in the Laboratório de Genética e Bioquímica of Embrapa Agrobiologia, were evaluated in this study. Among them, five strains were previously classified as potential ammonium excreting mutants and 20 as auxin overproducing mutants. The analyses showed that the mutant strains of G. diazotrophicus did not exhibit significant ammonium excretion in vitro; however, strains EDA-3 and EDA-4 promoted significant increases in biomass and plant growth in the early development stages when compared to the wild-type strain, suggesting the involvement of other physiological mechanisms. Regarding the mutant strains of A. baldaniorum Sp245, the results showed that strain FT-16 produced almost twice the amount of indolic compounds compared to the wild-type. In experiments with BRS Esmeralda rice, strains FT-16 and FT-14 stood out due to their positive effect on growth, both in the initial phase and throughout the crop cycle. Despite the positive effect of the mutant strain FT-14, it showed low production of indolic compounds compared to the wild-type strain. The results demonstrate the potential of using mutagenesis and selection by metabolic analogs as a strategy for developing promising inoculants with a greater capacity to promote plant growth.