Cuantificación de inóculo de Macrophomina phaseolina (Tassi) Goid en parcelas de soja del Departamento de Itapúa-Paraguay

The density of viable microsclerotia of the plant pathogen Macrophomina phaseolina in the soil is related to the intensity of the charcoal rot, which causes significant losses in soybean yield in Paraguay. During January 2017 and again in May 2019, soil samplings were carried out in soybean plots in 5 districts of the Department of Itapua (Edelira, Tomas Romero Pereira, Capitan Meza, Natalio and San Rafael), during the reproductive phenological stages (R1-R7) with the objective of quantifying the amount of M. phaseolina inoculum in soils with soybean crops. At the time of sampling, a questionnaire was carried out to the owners about the previous crop rotation in their fields. The presence of M. phaseolina was detected in 100% of the sampled points. The inoculum density varied from 7 to 147 CFU/g of soil, with an average of 50.5 CFU/g of soil and a median of 48 CFU/g of soil in 2017, while in 2019 the inoculum density varied from 6 to 49 CFU/g of soil, with an average of 25.07 CFU/g of soil and a median of 23 CFU/g of soil. Lower inoculum density was observed in plots with canola-soybean-soybean crop rotation with averages of 30 and 12 CFU/g of soil. The results of this survey will allow to guide future experimental works focused on exploring possible effects of crop rotations in soybean crops on the inoculum density of M. phaseolina.