Biotechnological potential of bacteria from genera Bacillus Paraburkholderia and Pseudomonas to control seed fungal pathogens

Abstract

Fungal pathogens are important determinants of plant dynamics in the environment. These pathogens can cause plant death and occasionally yield losses in crops, even at low initial densities in the soil. The objective of this study was to select and evaluate fungal antagonistic bacteria and to determine their biological control capacity in soybean seedlings. A total of 877 strains from the genera Pseudomonas, Bacillus, and Paraburkholderia/Burkholderia were screened, and their antagonistic effects on fungi frequently found in seeds were evaluated using four methods: quadruple plating, paired culture confrontation, strain containment, and inoculation of soybean seeds. The experimental design was completely randomized, with three replications for the first three methods and five replications in a 3 × 9 factorial scheme for the fourth treatment. The strains with the highest biotechnological potential were inoculated into soybean seeds to evaluate the biological control of fungi that attack this crop at germination. Seventy-nine strains presented some type of antagonistic effect on the tested fungi, with two strains presenting a broader antagonistic action spectrum in the seed test. In addition to the antagonistic potential, strains BR 10788 and BR 11793, when simultaneously inoculated or alone, significantly increased the seedling dry matter mass, and promoted the growth of soybean seedlings even in the presence of most fungi. Thus, this study demonstrated the efficiency of the antagonistic activity of these strains in relation to the target fungi, which proved to be potential agents for biological control.

Keywords: Bacillus; Biocontrol; Bioprospecting; Paraburkholderia; Screening.

Fig. 1

Phylogenetic tree of isolates based on 16S rRNA (1250 nt) of the genera Pseudomonas, Bacillus, and Burkholderia/Paraburkholderia tested for the biological control of the fungi Fusarium piperis, Fusarium semitectum, Pleosporales, Cladosporium sp., Phomopsis sojae, Rhizoctonia solani, Corynespora cassiicola, Sclerotinia sclerotiorum, and Aspergillus flavus. The numbers shown before the strains indicate the type of strain groups to which they belong and the number in parentheses indicates the number of fungi controlled by the strain and the scale

Fig. 2

Containment test for the control evaluation of the BR 10788 and BR 11793 strains with the fungal pathogens Aspergillus flavus, Pleosporales, Fusarium semitectum, Phomopsis. sojae, Sclerotinia sclerotiorum, Corynespora cassiicola, Cladosporium sp., Fusarium piperis, and Rhizoctonia solani. Column (A) Control; column (B) BR 10788; column (C) BR 11793. Row 1, Aspergillus flavus; row 2, Pleosporales; row 3, Fusarium semitectum; row 4, Phomopsis. sojae; row 5, Sclerotinia sclerotiorum; row 6, Corynespora cassiicola; row 7, Cladosporium sp.; row 8, Fusarium piperis; row 9, Rhizoctonia solani