Improving quality and yield of maize by foliar application of Azospirillum and Pseudomonas

TRAVAGLIA CLAUDIA; MASCIARELLI OSCAR; CARDOZO PAULA; FORTUNA JULIETA ; MARCHETTI GISELLA; REINOSO HERMINDA

La Falda, Córdoba

Workshop; II Latin American PGPR; 2014

The rhizosferic bacteria have a beneficial effect on plants growth. Azospirillum and Pseudomonas are the most studied genera of PGPR, due to their capacity to enhance growth and development significantly as well as the yield of numerous vegetable species of agricultural interest. Besides the capacity to promote growth, it has been shown that Azospirillum and Pseudomonas are able to tolerate herbicides and degrade xenobiotics. Herbicides use in the control of weeds is an important factor in current agriculture that constitutes a practical and generalized practice. In this sense, Glyphosate (N-phosphonomethyl glycine), is one of the non-selective broad-spectrum herbicides most widely used in the world. Its excessive use could have potentially toxic effects in crops products, what justifies the increasing concern at all levels associated with food safety. This is why the objective set is to evaluate the capacity of Azospirillum and Pseudomonas to degrade glyphosate residues, in both, in Vitro conditions as well as in Vivo in maize plants at different growth stages, with the aim of improving the quality of crops in a sustainable way. To evaluate the capacity of PGPRs to tolerate and degrade glyphosate, preinocules were cultured ?over night? in LB medium and commercial herbicide or thus pure glyphosate active ingredient was added (1.3 ppm). The biomass growth phase was measured through optical density (DO590nm). Also, experiments were performed under controlled conditions in a growth chamber and field with maize (Zea mays L.) plants (DK670MGRR). The treatments were: Herbicide foliar application; Herbicide foliar application + foliar inoculation with Azospirillum sp.; Herbicide foliar application + foliar inoculation with Pseudomonas sp. the bacterial suspension of both PGPR was of 1L/100 L and were applied in vegetative phonological stages (V6) and repeated previous to the flowering reproductive stage (R1). The herbicide application based on glyphosate was done by spraying 48% isopropilamine salt glyphosate at the V3 and V6 stage. The concentration used was 2.5 L/100 L. Physiological and anatomical parameters in maize plants at different growth stages were analyzed, as well as the herbicide residual content in leaves and grains were determined at physiological maturity. Under in Vitro conditions, both bacteria (Azospirillum and Pseudomonas) tolerated the glypshosate and showed capacity to use it as a carbon source. In these assays performed in early growth stages, inoculation with both bacteria with herbicide improved germination behaviour significantly and root emergency, being superior in the treatment with Pseudomonas sp.. A greater length was also observed in the primary roots and radical hair and coleoptile development in the treatment with both PGPRs. The plants with the Azospirillum and Pseudomonas sp. application in the presence of herbicide improved the radical and shoot biomass, increased foliar area as well as the photosynthetic pigment and phytohormone (AIA, ABA) content, in comparison with the ones that did not receive such foliar bacterial inoculation. These bacterial applications had the capacity to mitigate herbicide accumulation in leaves and grains. A yield increase in the crops treated with Azospirillum and Pseudomonas was observed. This research shows that novel detoxification capabilities and the ability of these isolates to utilize glyphosate effectively provide a means of removing this compound from the environment. Thus, the biological compounds application in crops will not only have importance to enhance crop growth, development and yield, but also to improve the soil geochemical cycles, since they will allow a reduction in the excessive chemical fertilization and will minimize persistence of xenobiotics compounds, widely used in current agriculture practices.