Biological control of the soybean sudden-death-syndrome fungus Fusarium tucumaniae by Pseudomonas sp. strain SMMP3

AGARAS, B; SCANDIANI M; LUQUE A; CARMONA M; WALL LG; VALVERDE C

Mar del Plata

Congreso; VIII Congreso Argentino de Microbiología General SAMIGE; 2012

SAMIGE

Sudden Death Syndrome (SDS) is a soybean disease caused by at least four Fusarium species. This complex disease emerged in Arkansas in 1972 and established in the Pampean and Northwest regions of Argentina since 1991, with F. tucumaniae and F. virguliforme species being the local predominant agents. The fungus infects soybean roots and, under appropriate conditions, toxin-dependent symptoms develop in the aerial tissues after flowering and during pod fill, leading to rapid necrosis. Highly resistant soybean cultivars are not available and chemical control of SDS is only partially effective. In this context, biological control appears as an alternative and interesting tool. Pseudomonas spp. strains are widely recognized for their ability to antagonize the growth of fungal pathogens. The Pseudomonas strain SMMP3, a member of the P. chlororaphis complex, was isolated from an agricultural bulk soil sample from Monte Buey (Córdoba). Isolate SMMP3 is a highly motile bacterium that produces HCN, extracellular protease, and an orange diffusible pigment, which may be a phenazine compound synthesized by the product of the detected phzF gene. SMMP3 antagonizes the growth of several pathogenic fungi, including the F. tucumaniae isolate CCC 132-11 (diameter of growth inhibition halo = 12.5 ± 4.8 mm, in potato dextrose agar). The ability of strain SMMP3 to reduce the incidence of soybean SDS was tested under greenhouse conditions and in the field. Soybean seeds from a susceptible cultivar (NA 4613RG) were treated with a suspension of SMMP3 cells (0.3 ml at OD600 = 1.0 per 50 g of seeds), and immediately sown in pots containing a commercial substrate (GrowMix) artificially infested with a F. tucumaniae CCC 132-11 inoculum. In parallel, treated seeds were sown in a plot located in Pergamino (Buenos Aires) with a documented history of soybean SDS. Inoculation with SMMP3 delayed the onset of SDS and reduced foliar damage under greenhouse conditions, in two independent experiments. Both, in the greenhouse and in the field, seed treatment with strain SMMP3 resulted in a reduction of SDS ratings (incidence, severity) and of the AUDPC values (area under disease progress curve). In the field trial, treated plants showed a 10.4% increment in grain yield (kg/ha). These effects, however, were not statistically meaningful (P>0.05). This positive trend must be confirmed with additional field trials. Altogether, these results suggest that strain SMMP3 displays biocontrol features both in vitro and in planta against F. tucumaniae CCC 132-11, one of the causing agents of soybean SDS. Additional tests (like seed treatment with strain SMMP3 and with a chemical antifungal product, or multiple strain inoculation) might be required to improve the degree of SDS control.