Abstract

Pythium spp. are the most common pathogens associated with soybean damping-off in the United States. The diversity of Pythium spp. recovered is extensive and the relative pathogenicity or aggressiveness of species common across states has varied among studies. We compared the aggressiveness and fungicide sensitivity of 118 isolates of four Pythium spp. (P. lutarium, P. oopapillum, P. sylvaticum, and P. torulosum) from 11 states (AR, IA, IL, IN, KS, MI, MN, ND, NE, SD, and WI). All isolates were screened using seed and seedling assays at two temperatures (13°C and 23°C). Seed rot and root rot severity varied by state of origin, with isolates from AR always the most aggressive. In general, isolates of P. sylvaticum and P. lutarium were more aggressive at 23°C compared with 13°C, while isolates of P. oopapillum and P. torulosum were more aggressive at 13°C than at 23°C. Fungicide sensitivity to five fungicides (metalaxyl, azoxystrobin, ethaboxam, captan, and thiram) was assessed using a plate assay at 13°C and 23°C. The EC₅₀ values for each fungicide-isolate combination varied by state of origin, and were greatest for the isolates from AR. Temperature affected EC₅₀ values for metalaxyl, azoxystrobin, and ethaboxam for P. oopapillum, P. sylvaticum, and P torulosum. The EC₅₀ values for thiram were not affected by temperature for any species. Results from this study indicate that aggressiveness and fungicide sensitivity of Pythium spp. vary geographically, which suggests that management of damping-off of soybean should target local rather than regional Pythium populations.

摘要

腐霉属 是与美国大豆猝倒病相关的最常见病原体。腐霉属的多样性。恢复的范围很广，各州常见物种的相对致病性或侵袭性在不同研究中有所不同。我们比较了四种腐霉属的 118 个分离株的侵袭性和杀菌剂敏感性。（P. lutarium、P. oopapillum、P. sylvaticum和P. torulosum）来自 11 个州（AR、IA、IL、IN、KS、MI、MN、ND、NE、SD 和 WI）。在两个温度（13°C 和 23°C）下使用种子和幼苗测定法筛选所有分离株。种子腐烂和根腐烂的严重程度因起源状态而异，来自 AR 的分离株总是最具攻击性。一般来说，分离株与 13°C 相比，P. sylvaticum和P. lutarium在 23°C 下更具攻击性，而P. oopapillum和P. torulosum 的分离株在 13°C 下比在 23°C 下更具攻击性。在 13°C 和 23°C 下使用平板测定法评估了对五种杀菌剂（甲霜灵、嘧菌酯、噻菌灵、克菌丹和福美双）的杀菌剂敏感性。每种杀菌剂-分离株组合的 EC ₅₀值因起源状态而异，并且对于来自 AR 的分离株而言最大。温度影响甲霜灵、嘧菌酯和噻唑菌胺的EC ₅₀值，用于P. oopapillum、P. sylvaticum和P torulosum。欧共体₅₀福美双的值不受任何物种温度的影响。这项研究的结果表明腐霉属的侵袭性和杀菌剂敏感性。因地域而异，这表明大豆猝倒管理应针对当地而非区域腐霉种群。