Diversidade genética de Sinorhizobium spp. e eficiência simbiótica de associações bi e tripartites com Gliricidia sepium

Abstract

Gliricidia sepium (Jacq.) Kunth ex Walp. it is a tree legume of great commercial and economic interest in tropical regions. It is a species that is adaptable to a wide variety of soils, however nutritional limitations can reduce its development, among them nitrogen is the one that most commonly causes this limitation, with biological nitrogen fixation being the most important method of supplying nitrogen to the soil. system. Given the above, this work aimed to evaluate the symbiotic efficiency of coinoculation of Sinorhizobium strains with two Rhizobium strains (BR 8801 and BR 8802) in Gliricidia sepium. The evaluation of the phylogenetic relationships of the rhizobial isolates was carried out by sequencing the symbiotic genes nodC and nifH and the constitutive gene gyrB.11 strains belonging to the genus Sinorhizobium were evaluated, coinoculated with two strains of Rhizobium (BR 8801 and 8802), authorized by MAPA for the production of inoculants for G. sepium, in Brazil. To test the symbiotic efficiency of rhizobial strains, two experiments were carried out: the first in a greenhouse, with sterilized substrate and the second in a nursery with non-sterile soil. A total of 38 treatments with four replications in both experiments were evaluated, including: single inoculation of 11 Sinorhizobium; single inoculation of BR 8801 and 8802; 11 Sinorhizobium coinoculated with Rhizobium (BR 8801); 11 Sinorhizobium coinoculated with Rhizobium (BR 8802), BR 8801 coinoculated with BR 8802, a control treatment with nitrogen supply, supplied with NH4NO3 with application of 50 mg of N weekly and an absolute treatment, without inoculation and nitrogen application. In both experiments, the following variables were evaluated: dry mass of shoots and roots, number of nodules, dry mass of nodules, nitrogen content, total nitrogen and nodular efficiency. This study showed that there were inconsistencies between the phylogenies of symbiotic genes and the constitutive gyrB gene. In the phylogeny of the gyrB nine gene bacteria grouped with S. alkalisoli and two bacteria were close to S. terangae. In the sequencing of the nodC and nifH genes, the bacteria were close to S. americanum, with evidence of a possible horizontal transfer of symbiotic genes. Isolates of Sinorhizobium spp. showed potential for promoting the growth of gliricídia plants. Coinoculation proved to be a favorable practice, mainly due to the cooperation between Sinorhizobium spp. isolates. and references BR 8801 and 8802, with emphasis on bacteria G10, G19, G28, G44 and G49.