Abstract Multiple pathogens are frequently recovered together from diseased soybean seedlings, suggesting a seedling disease complex. Pythium sylvaticum and P. irregulare are prevalent oomycetes and Fusarium oxysporum and F. graminearum are prevalent fungi associated with seedling disease of soybean. We hypothesized that infection with multiple seedling disease pathogens would cause disease symptoms to be more severe than either pathogen alone. A cup assay was used to evaluate the effect of co-inoculation with Pythium and Fusarium species on soybean seedling disease development. Cups were inoculated with either Pythium alone, Fusarium alone, or co-inoculated with both genera. Non-inoculated cups were used as a control. Cups were sampled at 2, 4, 6, 8 and 10 days after planting (DAP) and disease severity (DS), emergence (EME) and wet root weight (WRW) were determined. Isolations on selective media were done to determine pathogen prevalence. Seedling disease was more severe in cups inoculated with Pythium compared with those inoculated with Fusarium alone. No difference in disease development was observed for the Pythium species tested, but more severe disease occurred on seedlings inoculated with F. graminearum compared with those inoculated with F. oxysporum. Generally, there was little difference in disease development between treatments inoculated with Pythium alone and those co-inoculated with Pythium and Fusarium. Over time, an increase in DS and WRW was observed in Pythium+Fusarium treatments and there was no effect of time on EME. Under the conditions used in these experiments, co-inoculation with Pythium and Fusarium did not result in more severe seedling disease on soybean.

中文翻译：

---

腐霉和镰刀菌共接种对大豆幼苗病害发展的影响

摘要 多种病原体经常从患病的大豆幼苗中一起回收，表明幼苗病害复杂。Pythium sylvaticum 和 P.informale 是流行的卵菌，Fusarium oxysporum 和 F. graminearum 是流行的与大豆苗病相关的真菌。我们假设感染多种幼苗疾病病原体会导致疾病症状比单独的任一病原体更严重。杯法用于评估与腐霉和镰刀菌共接种对大豆幼苗疾病发展的影响。杯子用单独的腐霉属、单独的镰刀菌或与两种属共同接种。未接种的杯子用作对照。在种植 (DAP) 和疾病严重程度 (DS) 后 2、4、6、8 和 10 天对杯子取样，测定出苗（EME）和湿根重（WRW）。在选择性培养基上进行分离以确定病原体流行。与单独接种镰刀菌的杯相比，接种腐霉的杯中的幼苗病害更严重。对所测试的腐霉属物种没有观察到病害发展的差异，但与接种尖孢镰刀菌的幼苗相比，接种禾谷镰刀菌的幼苗发生了更严重的病害。通常，单独接种腐霉的处理与接种腐霉和镰刀菌的处理之间的疾病发展几乎没有差异。随着时间的推移，在腐霉+镰刀菌处理中观察到 DS 和 WRW 增加，并且时间对 EME 没有影响。在这些实验中使用的条件下，