Chitosan-Bradyrhizobium compatibility applied to seeds and its effect in the vegetative development of soybean (Glycine max (L.) Merrill)

Abstract

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.