Symbiotic effectiveness of Bradyrhizobium ingae in promoting growth of Inga edulis Mart. seedlings

Abstract

Inga edulis Mart. is a leguminous tree adapted to acidic and low-fertility soils that establishes symbioses with nitrogen (N)-fixing bacteria. The identification of effective bacteria in biological N fixation may bolster the use of I. edulis in degraded or modified areas and agroforestry systems. Therefore, the aims of this study were evaluation of the symbiotic effectiveness of eight strains of the Bradyrhizobium genus native to Roraima in Inga edulis plants, and in vitro evaluation of the ability of the eight strains of Bradyrhizobium to develop plant growth-promoting characteristics. Determination of symbiotic effectiveness was carried out via three experiments: the first in a greenhouse in pots with a sterile substrate; the second in a greenhouse in pots containing non-sterile soil; and the third in a nursery in bags with a non-sterile substrate. Twelve treatments were evaluated: inoculation with eight strains of Bradyrhizobium ingae (ERR 490, ERR 492, ERR 493, ERR 494 T , ERR 496, ERR 497, ERR 498, and ERR 569); inoculation with two strains indicated for Inga marginata, BR 6609 and BR 6610 (positive controls); no inoculation but with mineral N; and neither inoculation nor mineral N. All of the experiments were conducted in a completely randomized design with four replicates. The first experiment was conducted for 60 days, and the other experiments were conducted for 100 days. For all of the experiments, the number of nodules, nodule dry matter, root dry matter, shoot dry matter, number of leaflets, plant height, stem diameter, total N in the shoots, root/shoot dry matter ratio, Dickson's quality index, relative effectiveness, and the Pearson correlation between the variables under study were evaluated. The strains were also evaluated by their ability to solubilize calcium and aluminum phosphates and to produce indolic compounds. The results showed that B. ingae strains were effective in biological N fixation, especially the ERR 493, ERR 498, and ERR 569 strains. These strains increased the production of shoot dry matter and total N and exhibited relative effectiveness higher than 100 % in all of the experiments. The B. ingae strains were also able to solubilize calcium and aluminum phosphates, despite their synthesis of indolic compounds. Thus, the strains of B. ingae can be used for inoculation in the production of I. edulis seedlings.

GROWTH RESPONSE OF Bauhinia Variegata L. TO INOCULATION AND ORGANIC FERTILIZATION

“…There was also a higher mean value (9.76 leaves -1 ) observed in B. forficata seedlings when using cow urine at a concentration of 5% (Raulino et al, 2015). However, fertilization with organic compost reduced the number of leaves in Moringa oleifera (Medeiros et al, 2017). In B. variegata proportions higher than 20:80 (compost:soil) reduced the number of leaves.…”

“…It was also verified that, independently form nodulation, there was a positive effect from inoculation over seedling height, dry mass of the aerial portion and roots, total dry mass, IQD and foliar contents of N and C. These effects may be attributed, probably not only to the capacity for biological fixation of N 2 , but also to the production of phytohormones (such as auxins, cytokinins and gibberellins) and solubilization of phosphates and exopolisaccharides by diazotrophic bacteria (Gumiere et al, 2014;Costa et al, 2016;Silva et al, 2016;Porto et al, 2016). As registered for strains of the genus Bradyrhizobium, which increased the production of Inga edulis (Porto et al, 2017), many arboreal species are responsive to inoculation, as also the normative from the Ministry of Agriculture, Livestock and Supply (Brasil, 2011) states, for approximately 23 arboreal legume species which have authorization to be inoculated in the seedling stage. Basic research work of selection or recommendation of inoculants evidences that inoculation stimulates vegetal growth of various species.…”

“…This compost represents an alternative to formulate cultivation substrates, once it shows satisfactory contents of macro and micro nutrients according to the Brazilian legislation (Brasil, 2009), defined by the classification of organic fertilizer, being precisely classified as Class A. This material shows potential to increase physical properties of the soil, such as water retention and preservation of chemical characteristics of the substrate, important issues which may influence directly on foliar and radicular growth of seedlings (Delarmelina et al, 2014;Medeiros et al, 2017).…”

“…Organic residues from agricultural or urban activities, after being processed by composting, render an organic material with desirable characteristics to produce substrates for seedling production. Positive results obtained by mixing residues are observed in arboreal species (Duarte and Nunes, 2012;Sousa et al, 2013;Cavalcante et al, 2016;Medeiros et al, 2017). In addition to a significant reduction of environmental pollution through an adequate destination of residues, the use of organic residues contributes for crop production enabling the recycling of residues (Rodrigues et al, 2011) and the reduction of expenses with plant production.…”

“…In addition to the quality of the growth substrate, which depends on its nutrient availability (Delarmelina et al, 2014;Sousa et al, 2016;Krefta et al, 2017) and its physical attributes (Medeiros et al, 2017); the association or symbiosis between plants and bacteria may enhance the development of seedlings in the nursery (Ferreira et al, 2015;Freire et al, 2017;Porto et al, 2017) and in field conditions, when associated to organic substrates (Fernandes et al, 2017).…”