The plant-associated Bacillus amyloliquefaciens strains MEP218 and ARP23 capable to produce cyclic lipopeptides are effective in biocontrol of fungal soybean diseases

ALVAREZ, F; RODRIGUEZ, P; ESTANGA, U; COZZI, J; GIACOMO DONATO, J; FISCHER, S; JOFRÉ, E

Piriápolis

Congreso; XXV Reunión Latinoamericana de Rizobiología; 2011

ALAR

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a disease with a high incidence in soybean producing countries such as Argentina. The biological control of this disease, based on the inoculation of bacterial biocontrol agents, is considered a friendly environmental alternative to the indiscriminate use of chemical fungicides. Two previously isolated plant-associated Bacillus sp. strains, ARP23 and MEP218, able to inhibit the growth of fungal phytopathogens in vitro were subjected to further analysis to determine their taxonomic position as well as to identify the compounds responsible for their antifungal activity. Both strains, renamed as Bacillus amyloliquefaciens ARP 23 and MEP218, were able to produce antifungal compounds belonging to the cyclic lipopeptide family. Mass spectra from RP-HPLC eluted fractions showed the presence of surfactin C´ 5´ fengycins A (C ,6-C17) and B (C,6) isoforms in supernatants from strain ARP23 cultures, whereas the major lipopeptide produced by strain MEP218 was iturin A C,5. Additionally, genetic markers related to peptide synthetases involved in the biosynthesis of these cyclic lipopeptides were detected by PCR in the genomes of B. amyloliquefaciens strains. Moreover, alterations in mycelial morphology and sclerotial germination were observed in the presence of lipopeptides-containing supernatants from Bacillus strains cultures. Foliar application of B. amyloliquefaciens strains on soybean plants prior to S. sclerotiorum infection resulted in significant protection against sclerotinia stem rot compared to non-inoculated plants or plants inoculated with a non-lipopeptide producing B. subtilis strain. In order to evaluate the behavior of these bacterial strains under field conditions an inoculant based on B. amyloliquefaciens strains was formulated by the company NITRAP SRL. The viability of Bacillus strains as well as the activity of the metabOlites present in the inoculant remained one year. The effectiveness of the inoculant was evaluated in field trials during 2009-2010. The formu lation was used for foliar application on R5.3-stage soybean plants showing typical symptoms of Septaria brown spots (40% of incidence) and Cercospora leaf spot traces. A reduction in symptoms severity and a delayed defoliation were observed after 15 and 20 days post-application compared to non-treated plants. Average soybean yield was increased between 101 and 180 kg/ ha following Bacillus treatments with respect to non-treated plants. Moreover, the foliar application of Bacillus strains showed an increased soybean yield compared to the treatment with the chemical fungicide Amistar Xtra®. Our data suggestthatthe foliar application of lipopeptide-producing B. amyloliquefaciens strains could be a promising strategy for the management of soybean diseases.