Effect of Mn phosphite seed treatment on development of soybean sudden death syndrome (SDS) caused by Fusarium tucumaniae

CARMONA M.; FORMENTO N.; LUQUE A.; LENZI L.; TARTABINI M.; SAUTUA F.J.; SIMONETTI E.; SCANDIANI M.

Durban

Conferencia; The World Soybean Research Conference IX; 2013

F. tucumaniae is the primary causal agent of sudden death syndrome (SDS) of soybean in Argentina. It is a soil borne pathogen that causes root rot followed by the development of foliar symptoms, causing yield losses. Early infections, occurring at seed stage, produced foliar symptoms and the higher root rot severity, when compared to later infections. The objectives of this study were to investigate the efficacy of a new Mn phosphite formulation as a seed treatment to control SDS under greenhouse and field conditions. Soybean seeds were treated with Mn Phi (Ultra Plus Mn 200cc/100kg of seed). Phosphites have a complex mode of action, ranging from direct action against invading pathogens to indirect effects, such as activation of host defense response. Phosphite is translocated both upward and downward due to its mobility in both xylem and phloem. In greenhouse, five seeds of susceptible soybean cv. NA 4613RG previously treated of each treatment, were sowed in artificially infested pots. Fusarium tucumaniae CCC 130-11 grown on sorghum grains was used as inoculum. Untreated seeds sown on infested pots were used as a positive control, while untreated and uninfested seeds were used as the negative control. The experiments were conducted in a greenhouse under a natural photoperiod at 25±3 C for 25 days, with the pots arranged in a randomized complete block design with four replications. Foliar symptoms were assessed at four time intervals after inoculation. Disease severity was used to determine the area under the disease progress curves (AUDPCs). At the end of the experiment, plants were assessed for root rot, plant height, and shoot and root dry weight. Field plots were established in Pergamino (Buenos Aires province) with a documented history of soybean SDS. Control and Mn Phi treatment were arranged in a randomized block design with four replicates per treatment. Foliar disease symptoms were rated weakly. The soybean seeds treated in this study were not affected negatively by the Mn Phi and the plants did not show phytotoxicity effects. Both, in the greenhouse and in the field, seed treatment with Mn Phi resulted in a reduction of SDS ratings (plant incidence, foliar severity) and in the AUDPCs values. In greenhouse the Mn Phi reduced (no significant) the root rot severity evaluated at the end of the trial. In the field trial, a 24% (3681 vs. 4595 kg/ha; P