Daimy Costales-Menéndez

Introduction. Legume nodulation is regulated by the exchange of molecular signals between the plant and rhizobia. The bacterial nodulation genes are activated by flavonoids present in root exudates. As a result of this activation, the Nod factors are synthesized, which in turn participate in the morphogenesis and function of the nodules. It is then possible to regulate the induction of Nod factors and other signals related to the nodulation process, during the inoculants production. Objective. To determine if the moment to induce the nodulation genes in Bradyrhizobium inoculants affects the synthesis of compounds related to the nodulation process and its interaction with soybean plants. Materials and methods. The research was developed in Rizobacter S.A., Argentina and Fyteko S.A. laboratories, Belgium, and in a plant growth chamber of the first one, during May-June of 2017. Two Bradyrhizobium strains were induced with daidzein in three moments. The signals produced by the strains and the biological effect in soybean plants were studied. Results. Differences were detected in the molecules produced by the bacteria, but it did not affect the growing and plants nodulation related to the different moments of induction. Conclusion. The metabolites excreted by Bradyrhizobium changed with strain and induction moment, although the latter did not affect nodulation or soybean plants growth.

Introduction. Chitosan and plant growth promoting rhizobacteria are recognized as agricultural biostimulants for the biological benefits they provide to plants. Objective. To evaluate the combined application of chitosan concentrations and the Azofert-S¨ inoculant on soybean seeds, on the survival of Bradyrhizobium elkanii and the vegetative growth of the plants. Materials and methods. The research was developed in the plant growth room of Plant Physiology and Biochemistry Department of the Instituto Nacional de Ciencias Agricolas, Cuba, in 2016. The effect of chitosan and Azofert-S¨ inoculant applied to soybean seeds was determined on the number of viable bacteria in seeds and the behavior of morphoagronomic and physio-biochemical indicators related to the nodulation and vegetative development of plants. Results. The chitosan concentrations evaluated in the compatibility test did not affect the number of viable cells in the seeds, except for 500 and 1000 mg l-1, which improved the bacteria survival at the beginning of the test and 500 mg l-1 at ten days of seed storage. The latter concentration also benefited root and stem length, leaf area, and nitrate reductase enzymatic activity in leaves. The combined application of Azofert® - chitosan and seed inoculation alone enhanced the concentration of nitrogen and other nutrients in nodules and trifoliolus. The concentration of flavonoids and total phenols increased with the concentration of 10 mg l-1 of chitosan, although it decreased the concentration of total soluble and reductive carbohydrates in leaves. Conclusion. The biostimulants were compatible when applied on seeds at the time of sowing and benefited the nodulation, nutrition, and vegetative development of soybeans plants, depending on the concentration of the polymer.

The objective of this study was to evaluate the effect of a mix of pectic oligosaccharides in the common bean-rhizobia symbiosis. Cuba Cueto-25-9-N bean seeds were inoculated with Rhizobium tropici CIAT 899 and treated with a mix of oligogalacturonides, either by application to the seed (10 mg L^-1, 1 ml per seed) at sowing and inoculation or by foliar spray (5 or 100 mg L^-1, 1.5 ml per plant) to plants with two trefoils. Plant growth, nodulation, nitrogenase activity, and the gene expression of glutamine synthetase and glutamate synthase in nodules were evaluated in inoculated plants and oligogalacturonide-treated inoculated plants at 18 d post-inoculation. The oligogalacturonide-treated plants showed increases in shoot and root growth and number of nodules. Regarding nodule function, the oligogalacturonides increased the nitrogenase activity and the expression level of the gene coding for NADH-dependent glutamate synthase. The positive effects of oligogalacturonides resulted in higher effectiveness of the symbiotic nitrogen fixation. The application of oligogalacturonides can offer an alternative to increasing the symbiotic nitrogen fixation in common bean plants. El objetivo de este estudio fue evaluar el efecto de una mezcla de oligosacáridos pécticos en la simbiosis frijol común-rizobios. Las semillas de frijol Cuba Cueto-25-9-N se inocularon con Rhizobium tropici CIAT 899 y se trataron con una mezcla de oligogalacturónidos por aplicación a la semilla (10 mg L^-1, 1 ml por semilla) en el momento de la siembra e inoculación o por aspersión foliar (5 o 100 mg L^-1, 1.5 ml por planta) a plantas con dos trifoliolos. A los 18 d después de la inoculación, se evaluó el crecimiento de las plantas, la nodulación, la actividad nitrogenasa y la expresión génica de la glutamina sintetasa y la glutamato sintasa en nódulos de plantas inoculadas y en plantas inoculadas y tratadas con oligogalacturónidos. Las plantas tratadas con oligogalacturónidos mostraron aumentos en el crecimiento del vástago y raíces y en el número de nódulos. En cuanto a la función de los nódulos, los oligogalacturónidos aumentaron la actividad nitrogenasa y el nivel de expresión del gen que codifica la glutamato sintasa dependiente de NADH. Los efectos positivos de los oligogalacturónidos resultaron en una mayor efectividad de la fijación simbiótica del nitrógeno. La aplicación de oligogalacturónidos puede ofrecer una alternativa para incrementar la fijación simbiótica del nitrógeno en plantas de frijol común.

Chitosan is applied to stimulate seed germination and to extend in various crop species. The aim of this work was to evaluate a chitosan polymer on the viability of Bradyrhizobium japonicum on seeds and their effect to improve seed and bacteria survival and soybean nodulation in two application sequences inoculant- polymer and different storage times. The polymer did not affect the bacteria viability on seeds, neither seed survival. The application of chitosan before the inoculant had the best percentages of germinated seeds and the seedlings quality. Chitosan concentrations between 100 and 1000 mg L-1 favoured germination, the number of bacteria colonies on seeds and the soybean nodulation until 30 days of seed storage.