Abstract
ABSTRACT Technologies that use rhizobacteria to promote plant growth are increasing in agriculture, results have shown improvements in soil quality, increases in productivity, and decreases in the use of synthetic inputs, The objective of work was to characterize bacterial isolates regarding their biological activity and growth promotion of soybean plants grown in a controlled environment. Fifteen bacteria were isolated from soils with continuous use of biological fertilizer. They were evaluated for enzymes production (amylase and protease), nitrogen fixation, antagonistic activity to phytopathogenic fungi, and indoleacetic acid (IAA) production, Soybean seeds were inoculated with bacterial isolates in a greenhouse and evaluated for plant development and soil chemical attributes. The results showed that 8 of the 15 isolates presented production of amylase, protease, or both and 4 isolates presented nitrogen-fixing capacity. The percentage of isolates with high or moderate inhibitory action against the fungi Sclerotinia sclerotiorum, Macrophomina phaseolina, and Fusarium solani were 73.3%, 66.6%, and 73.3%, respectively. The IAA production varied from 8.56 to 31.33 µg mL-1 (5 isolates had low, 6 had moderate, and 4 had high production). The soybean development was significantly higher in 80% of the treatments with inoculation with bacterial isolates. Five bacterial isolates effectively present all characteristics for use as inoculant (biofertilizer) to promote the development of soybean plants.
Highlights
The rhizosphere is a changeable habitat; its composition and structure are affected throughout the vegetative cycle of plants (TERRA et al, 2019)
Plant growth promoting rhizobacteria (PGPR) promote plant growth by colonizing roots; they are essential in assisting the plant establishment and development under nutrient deficit conditions (BENEDUZI; AMBROSINI; PASSAGLIA, 2012)
Ten grams of root soil of each sample was suspended in 90 mL of a saline solution (NaCl 0.85%), and subjected to serial dilution (1/10) up to 10-6 and incubated at 28 °C for 48 to 72 hours, the last three dilutions were plated in tryptone soy agar (TSA)
Summary
The rhizosphere is a changeable habitat; its composition and structure are affected throughout the vegetative cycle of plants (TERRA et al, 2019). The soil microbial community population varies according to the plant species; the release of exudates by the root can cause chemical and physical changes in the rhizosphere, which benefits or inhibits microbial growth in this region. Plant growth promoting rhizobacteria (PGPR) promote plant growth by colonizing roots; they are essential in assisting the plant establishment and development under nutrient deficit conditions (BENEDUZI; AMBROSINI; PASSAGLIA, 2012). This developmental stimulus to plants can be caused by different direct and indirect forms of action, such as the increase in nutrient availability, mainly phosphorus, caused by the solubilization of P forms of low solubility; increase in nitrogen, by biological fixation of atmospheric nitrogen; production of phytohormones; and control of pathogens (MANRIQUE et al, 2019).
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