EVALUATION OF INDIGENOUS BACTERIAL STRAINS FOR BIOCONTROL OF THE FROGEYE LEAF SPOT OF SOYBEAN CAUSED BY Cercospora sojina

SIMONETTI ESTER; CARMONA, MARCELO A; SCANDIANI, M.M.; BALESTRASSE, KARINA; CORREA, OLGA S.; FERRI, M.; LUQUE, A,G,; KERBER NORMA L.; PUCHEU, NORMA L; RAVOTTI, M; GARCÍA, AUGUSTO F.

Soja. Investigación Científico-Técnica desarrollada en el. INBA (CONICET-FAUBA) y en la Facultad de Agronomía de la UBA

Editorial de la Facultad de Agronomía (EFA)

Lugar: Ciudad Autónoma de Buenos Aires; Año: 2011; p. 161 - 167

ABSTRACT Frogeye Leaf Spot (FLS) caused by the fungus Cercospora sojina is one of the most important soybean diseases in Argentina and has caused severe losses in yield throughout the main soybean- growing areas. Among the new and possible environment-friendly strategies, the use of biological control methods seems to have potential for management of this disease. In this study, biocontrol capacity of three indigenous bacterial strains, Pseudomonas fluorescens BNM297 Bacillus amyloliquefaciens BNM340 and B. amyloliquefaciens BNM122, against C. sojina was tested in vitro and on soybean plants. From cultures of each strain, cell suspensions (108 CFU mL-1) and extracellular filtrates were obtained and assayed to determine their antifungal activity. Both, mycelial growth and spore germination in vitro, were more strongly inhibited by bacterial cell suspensions than by bacterial supernatants. Only the cell-free filtrate of BNM122 showed strong inhibitory activity by inducing unusual swelling in the conidia and the germ tubes of the fungus, probably by the production of lipodepsipeptides, previously characterized in this bacterium isolate. The foliar application of the two Bacillus strains on soybean seedlings was effective in reducing the disease severity caused by C. sojina. Both spray-applied bacteria; BNM340 and BNM122, significantly reduced the Disease Severity Index to a similar degree (DSI = 1.55 and 1.65, respectively), with respect to control (DSI = 2.61). Our data demonstrate that the application of antagonistic bacteria represents a promising alternative to control the FLS disease. To our knowledge, none indigenous bacterial strains have previously been assayed as biocontrol agents against FLS caused by C. sojina.