Growth promotion of maize (Zea mays L.) by rhizobacteria associated with the culture of guarana (Paullinia cupana var. sorbilis)

Author(s)

Bruna Durante Batista

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2013-02-04

Examining board members

Aline Aparecida Pizzirani kleiner; Paulo Teixeira Lacava; Maria Carolina Quecine Verdi

• Advisor: Aline Aparecida Pizzirani kleiner

Abstract

The use of mineral fertilizers on agricultural crops, including maize, is a practice that causes environmental damage and economical losses. A promising alternative, to improve productivity and reduce fertilizer use is the use of benefical microrganisms associated with plants, particulary the growth-promoting rhizobacteria. These bacteria live in the rhizosphere and are capable of colonizing different plant tissues, benefiting plant growth through mechanisms of growth promotion. In the search for sustainable and more profitable alternative, this study aimed to isolate, characterize, monitor and select rhizobacteria associated with Amazonian guarana that possessed characteristics of plant growth promoters for use as inoculants in maize seeds. Rhizosphere soil samples from five guarana plants were collected and the isolation of rhizobacteria was performed. Molecular characterization was performed by sequencing the 16S rDNA for analysis of microbial diversity and identification of strains. It was evaluated the ability of strains to produce indole acetic acid (IAA), fix atmospheric nitrogen, solubilize inorganic phosphate and produce siderophores. The analysis of microbial diversity indicated similarity between the bacterial community isolated from the rhizosphere of guarana and that found in the literature to maize. It was observed predominance of Proteobacteria phylum, being mostly represented by the genus Burkholderia. Of the total 101 strains obtained, 89% were able to produce IAA, 23% fixed atmospheric nitrogen, 43% solubilized inorganic phosphate and 24% produced siderophores. Five strains were selected for testing growth promotion of maize under greenhouse conditions; these were identified by complete sequencing of the 16S rDNA and compose the treatments as follows: RZ2MS9 - Bacillus sp. (T1), RZ2MS16 - Burkholderia ambifaria (T2) and consortium (T3) of 5 strains (RZ1MS6 - Burkholderia vietnamiensis, RZ1MS11 - Burkholderia sp., RZ2MS9 - Bacillus sp., RZ2MS16 - Burkholderia ambifaria and RZ4MS18 - Delftia acidovorans). Statistical analyzes showed that the strains RZ2MS9 (Bacillus sp.) and RZ2MS16 (Burkholderia ambifaria) were effective as growth promoters in maize, increasing the height about 39 and 33%, respectively, compared to control, shoot dry weight about 236 and 114% and root system about 248 and 136%, respectively, compared to uninoculated control. The strain RZ2MS9 (Bacillus sp.) increased Ca content in inoculated plants. For monitoring of colonization of the bacteria in the plant, the strain RZ2MS16 (Burkholderia ambifaria) was transformed with the plasmid pCM88 and passed to express GFP, being possible to observe by fluorescence microscopy that, 12 days after inoculation on the plant, the bacteria is concentrated in the root central cylinder where the same can be inserted into a vessel conductor and consistently colonize the plant, proving the endophytic life style of this strain during maize interaction. Thus, it is clear the importance of tropical plants, like guarana, as reservoirs of bacteria with great biotechnological potential. The evaluated bacteria accessed in this work have great potential to be used in future as inoculants. (AU)

• FAPESP's process: 11/05204-8 - Plant growth promotion by rhizobacteria of guarana.
• Grantee: Bruna Durante Batista
• Support Opportunities: Scholarships in Brazil - Master