Aims:  This work was conducted to identify the antifungal compounds produced by two previously isolated Bacillus sp. strains: ARP23 and MEP218. Both strains were subjected to further analysis to determine their taxonomic position and to identify the compounds responsible for their antifungal activity as well as to evaluate the efficiency of these strains to control sclerotinia stem rot in soybean. Methods and Results:  The antifungal compounds were isolated by acid precipitation of cell‐free supernatants, purified by RP‐HPLC and then tested for antagonistic activity against Sclerotinia sclerotiorum. Mass spectra from RP‐HPLC eluted fractions showed the presence of surfactin C15, fengycins A (C16–C17) and B (C16) isoforms in supernatants from strain ARP23 cultures, whereas the major lipopeptide produced by strain MEP218 was iturin A C15. Alterations in mycelial morphology and sclerotial germination were observed in the presence of lipopeptides‐containing supernatants from Bacillus strains cultures. Foliar application of Bacillus amyloliquefaciens strains on soybean plants prior to S. sclerotiorum infection resulted in significant protection against sclerotinia stem rot compared with noninoculated plants or plants inoculated with a nonlipopeptide‐producing B. subtilis strain. Conclusions:  Both strains, renamed as B. amyloliquefaciens ARP23 and MEP218, were able to produce antifungal compounds belonging to the cyclic lipopeptide family. Our data suggest that the foliar application of lipopeptide‐producing B. amyloliquefaciens strains could be a promising strategy for the management of sclerotinia stem rot in soybean. Significance and Impact of the Study:  Sclerotinia stem rot was ranked as one of the most severe soybean disease in Argentina and worldwide. The results of this study showed the potential of B. amyloliquefaciens strains ARP23 and MEP218 to control plant diseases caused by S. sclerotiorum.

The interaction between Azospirillum brasilense and plants is not fully understood, although several bacterial surface components like exopolysaccharides (EPS), flagella, and capsular polysaccharides are required for attachment and colonization. While in other plantb acteria associations (Rhizobium^legume, Pseudomonas^potato), lipopolysaccharides (LPS) play a key role in the establishment of an effective association, their role in the root colonization by Azospirillum had not been determined. In this study, we isolated a Tn5 mutant of A. brasilense Cd (EJ1) with an apparently modified LPS core structure, non-mucoid colony morphology, increased EPS production, and affected in maize root colonization. A 3790-bp region revealed the presence of three complete open reading frames designated rmlC, rmlB and rmlD. The beginning of a fourth open reading frame was found and designated rmlA. These genes are organized in a cluster which shows homology to the cluster involved in the synthesis of dTDP-rhamnose in other bacteria. Additionally, the analysis of the monosaccharide composition of LPSs showed a diminution of rhamnose compared to the wild-type strain. ß

In this study, we isolated bacteria from rhizosphere and endorhizophere of wheat crops of the central region of Argentina. The isolates were phenotypically characterized and the restriction patterns of 16S rDNA (ARDRA) using endonuclease AluI were analysed. Representative isolates were used to evaluate the effect of the inoculation on the growth of wheat under greenhouse conditions. The effects of plant growth-promoting bacteria on wheat plants were studied by evaluating shoot fresh and dry weights and root fresh and dry weights. One native strain increased the shoot and root dry biomass by 23% and 45% respectively. Other strains increased the shoot dry biomass. A 1.5 kb fragment of the 16S rRNA gene of one isolate was sequenced. This isolate showed high identity with different species of Pseudomonas.

A bacterial collection of approximately one thousand native strains, isolated from saline soils of Cordoba province (Argentina), was established. From this collection, a screening to identify those strains showing plant growth promotion and biocontrol activities, as well as salt tolerance, was performed. Eight native strains tolerant to 1 M: NaCl and displaying plant growth promotion and/or biocontrol features were selected for further characterization. Strains MEP(2 )18, MRP(2 )26, MEP(2 )11a, MEP(3 )1, and MEP(3 )3b significantly increased the growth of maize seedlings under normal and saline conditions, whereas isolates ARP(2 )3, AEP(1 )5, and ARP(2 )6 were able to increase the root dry weight of agropyre under saline conditions. On the other hand, strains MEP(2 )18 and ARP(2 )3 showed antagonistic activity against phytopathogenic fungi belonging to Sclerotinia and Fusarium genus. Antifungal activity was found in cell-free supernatants, and it was heat and protease resistant. Strains MEP(2)18 and ARP(2)3 were identified as Bacillus sp. and strains MEP(2)11a and MEP(3)3b as Ochrobactrum sp. according to the sequence analysis of 16S rRNA gene.

No abstract