Long-term non-irrigation (N-IRR) and irrigation (IRR) might affect pathogen communities causing seed-rot, root-rot, and damping-off of soybean. Characterization and quantification of Pythium, Fusarium, and Rhizoctonia spp. are critical for understanding the ecology of these microorganisms and management of root diseases. The populations and communities of Pythium, Fusarium, and Rhizoctonia were assessed in soils with long-term N-IRR and IRR using soil dilution plating, denaturing gradient gel electrophoresis (DGGE), and DNA sequence analysis. Disease incidences of seed-rot, root-rot, and damping-off of soybean were also evaluated with the soils from N-IRR and IRR in a growth chamber. Results showed that the population densities of Pythium and Rhizoctonia based on dilution plating and richness based on DGGE were significantly lower in soils with N-IRR than IRR, whereas the population densities of Fusarium and richness of Fusarium were significantly higher in soils with N-IRR than IRR. Cluster analysis based on DGGE band patterns demonstrated that the communities of Pythium, Fusarium, and Rhizoctonia were separated based on N-IRR and IRR. Species diversities of some Pythium, Fusarium, or Rhizoctonia were impacted differently in soils with N-IRR and IRR. Moreover, canonical correspondence analysis (CCA) showed that the disease incidences were positively correlated with levels of soil moisture, pH, the populations of Pythium and Rhizoctonia, richness of Pythium and Rhizoctonia, and negatively correlated with soil porosity, humic matter, and potassium. Long-term N-IRR and IRR could impact pathogen populations and communities and disease incidences differently, and the disease complex might be caused by different species under different systems.

长期不灌溉（N-IRR）和灌溉（IRR）可能会影响病原体群落，从而导致大豆的种子腐烂，根腐烂和变质。腐霉，镰刀菌和根瘤菌属菌种的表征和定量。对于理解这些微生物的生态学和根源管理至关重要。腐霉菌，镰刀菌属和根瘤菌属的种群和群落使用土壤稀释板，变性梯度凝胶电泳（DGGE）和DNA序列分析，对具有长期N-IRR和IRR的土壤进行了评估。还用生长室内的N-IRR和IRR土壤评估了大豆的种子腐烂，根腐和阻尼的病害发生率。结果表明，在人口密度腐霉和稻纹枯病基于稀释电镀和丰富性基于DGGE在与N- IRR比IRR土壤进行显著降低，而人口密度镰刀菌和丰富性镰刀菌在土壤中均显著高于与N- IRR比内部收益率 基于DGGE谱带模式的聚类分析表明，腐霉属，镰孢，和丝核菌基于N- IRR和IRR分离。在N-IRR和IRR的土壤中，某些腐霉，镰刀菌或根瘤菌的物种多样性受到不同的影响。此外，典范对应分析（CCA）表明，病害发生率与土壤水分，pH值的水平相关，的种群腐霉和丝核菌丰富的，腐霉和丝核菌，与土壤孔隙度，腐殖质和钾呈负相关。长期N-IRR和IRR对病原体种群和群落以及疾病发生率的影响不同，疾病复杂性可能是由不同物种在不同系统下引起的。