Rhizospheric bacteria of maize with potential for biocontrol of Fusarium verticillioides.

The stalk, ear and root rot (SERR) of maize caused by Fusarium verticillioides (Fv) severely impacts crop production in tropical and subtropical regions. The aim of the present work was to screen bacterial isolates in order to find novel native biocontrol agents against Fv. A culturable bacterial collection consisting of 11,520 isolates enriched in Firmicutes and Proteobacteria was created from rhizosphere samples taken from SERR symptomatic or asymptomatic maize plants. The complete collection was screened for potential activity against Fv using a liquid antagonism assay followed by dual cultures in solid medium, selecting for 42 bacteria (Bacillus, Pseudomonas and Paenibacillus) that inhibit Fv growth (>45 %). In planta assays demonstrated that three Bacillus isolates: B. megaterium (B5), B. cereus sensu lato (B25) and Bacillus sp. (B35) displayed the highest antagonistic activity against Fv. Pot experiments performed in a greenhouse with Bacillus cereus sensu lato B25 confirmed these findings and showed a reduction of Fv disease severity and incidence on plants. Antagonistic activity analysis revealed that these strains produce glucanases, proteases or chitinases, as well as siderophores and auxins and suggests these as possible control mechanisms against Fv.

Native soil bacteria isolates in Mexico exhibit a promising antagonistic effect against Fusarium oxysporum f. sp. radicis-lycopersici.

Sinaloa state accounts for 23% of Mexico's tomato production. One constraint on this important crop is the Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici, which has been reported to reduce crop yield by up to 50%. In this study, we set out to identify bacterial populations which could be used to control this disease through natural antagonism. Five tomato rhizospheric soil samples were collected, dried for 1-week, and homogenized. Sub-samples were used to prepare an aqueous solution used to isolate microorganisms in pure cultures. Organisms were purified and grown separately, and used to generate a collection of 705 bacterial isolates. Thirty-four percent from this bank (254 strains) was screened against Forl, finding 27 bacteria displaying in vitro Forl growth inhibition levels from 5% to 60%. These isolates belonged to the genus Bacillus and their 16Sr DNA sequences showed that they are closely related to seven species and they were putatively designated as: B. subtilis, B. cereus, B. amyloliquefaciens, B. licheniformis, B. thuringiensis, B. megaterium, and B. pumilus. One isolate belonged to the genus Acinetobacter. Two B. subtilis isolates (144 and 151) and one B. cereus isolate (171) showed the best antagonistic potential against FCRRT when evaluated on seedlings. Plate and activity assays indicate that these isolates include a diverse repertoire of functional antagonistic traits that might explain their ability to control FCRRT. Moreover, bacteria showed partial hemolytic activity, and future research will be directed at ensuring that their application will be not harmful for humans and effective against Forl in greenhouse or field conditions.