Survival of pathogens on soybean debris under no-tillage and conventional tillage systems

A study was conducted in the subtropical area of Southern Brazil to determi ne the survival of pathogens in soybean residues under conventional and no- tillage cultivation systems from March to September of 1998 and 1999. The p athogens most frequently isolated were Collelotrichum truncatum, Phomopsis spp., Cercospora kikuchii, Fusarium spp., Macrophomina phaseolina, and Rhiz octonia solani. Other fungi isolated were Myrothecium roridum, Penicillium sp., Chaetomium sp., Epicoccum sp., Corynespora cassiicola and Trichoderma sp. The percent of survival of each pathogen varied according to the month and the year. Survival of C truncatum, Phomopsis spp. and C kikuchii were s ignificantly reduced (p <0.05) from the first to the last evaluation either on buried debris or maintained on the soil surface. On the other hand, Af. phaseolina and Fusarium spp. were either not affected or favored by buryin g the debris. The frequency of recovery of Fusarium spp. increased speciall y in debris kept under the soil. The loss of biomass, measured by debris we ight along the period of this study, showed a reduction of 44.4% in the con ventional system and 34.9% in the no-tillage system in 1998, when rain was better distributed. In 1999, the reduction was 48.2% and 39.0% for the conv entional and no-tillage system, respectively.