Crop Rotation Effects on the Population Density of Soybean Soilborne Pathogens Under a No-Till Cropping System

Soilborne diseases are persistent problems in soybean production. Long-term crop rotation can contribute to soilborne disease management. However, the response of soilborne pathogens to crop rotation is inconsistent, and rotation efficacy is highly variable. Selection of proper crop plants and crop sequences for disease management is needed. In this research, the effects of crop rotation on soybean soilborne pathogens were evaluated in a long-term no-till crop rotation field trial in South Dakota. Five rotation treatments were evaluated in this field trial, including corn-soybean (<i>Zea mays</i> L., <i>Glycine max</i> [L.] Merr.), corn-soybean-spring wheat-pea (wheat: <i>Triticum aestivum</i> L., pea: <i>Pisum sativum</i> subsp. <i>arvense</i> [L.] Asch.), corn-soybean-spring wheat-sunflower (sunflower: <i>Helianthus annuus</i> L.), corn-oat-winter wheat-soybean (oat: <i>Avena sativa</i> L.), and corn-pea-winter wheat-soybean (CPWwS). Six soilborne pathogens that consistently threaten U.S. soybean production were quantified in the field soils using quantitative PCR or egg extraction for soybean cyst nematode. Three soilborne pathogens, <i>Macrophomina phaseolina</i>, <i>Fusarium oxysporum</i>, and <i>Pythium irregulare</i>, were detected, whereas the population density of <i>F. graminearum</i> and <i>F. virguliforme</i> was not measurable in the soil samples. The number of soybean cyst nematode eggs or juveniles was zero or very low in all soil samples. Overall, crop rotation treatments affected the population density of three detected pathogens but varied by crop phase, year, and pathogen species. The population density of three detected pathogens was positively correlated with soil temperature but negatively correlated with soil volumetric water content. Notably, the CPWwS rotation treatment had a consistently lower <i>M. phaseolina</i> population compared with the other rotation treatments, regardless of crop phase and year. This study provided potential crop sequences that limit soilborne pathogen populations in the soil and may reduce disease incidence on the host crops.