Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824.
Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849.
Plant Dis. 2022 Feb;106(2):425-431. doi: 10.1094/PDIS-03-21-0443-RE. Epub 2022 Feb 2.
Identifying the pathotype structure of a population is crucial for the effective management of Phytophthora stem and root rot of soybean (PRR). . has been successfully managed with major resistance genes, partial resistance, and fungicide seed treatments. However, prolonged use of resistance genes or fungicides can cause pathogen populations to adapt over time, rendering resistance genes or fungicides ineffective. A statewide survey was conducted to characterize this pathotype structure and fungicide sensitivity of . within Michigan. Soil samples were collected from 69 fields with a history of PRR and fields having consistent plant stand establishment issues. Eighty-three isolates of . were obtained, and hypocotyl inoculations were performed on 14 differential soybean cultivars, all of which carry a single gene or no resistance gene. The survey identified a loss of effectiveness of genes 1b, 1k, 3b, and 6, compared with a previous survey conducted in Michigan from 1993 to 1997. Three effective resistance genes were identified for . management in Michigan; 3a, 3c, and 4. Additionally, the effective concentration of common seed treatment fungicides to inhibit mycelial growth by 50% () was determined. No . isolates were insensitive to the tested chemistries with mean values of 2.60 × 10 μg/ml for ethaboxam, 3.03 × 10 μg/ml for mefenoxam, 2.88 × 10 μg/ml for oxathiapiprolin, and 5.08 × 10 μg/ml for pyraclostrobin. Results suggest that while there has been a significant shift in gene effectiveness, seed treatments are still effective for early season management of this disease.
鉴定种群的致病型结构对于有效管理大豆疫霉茎基和根腐病（PRR）至关重要。通过主要抗性基因、部分抗性和杀菌剂拌种处理，已成功管理了该病害。然而，抗性基因或杀菌剂的长期使用会导致病原体种群随着时间的推移而适应，从而使抗性基因或杀菌剂失效。在密歇根州进行了全州范围的调查，以描述该病害的致病型结构和杀菌剂敏感性。从有 PRR 病史的 69 个和一直存在植株定植问题的田地中采集土壤样本。共获得 83 个疫霉菌分离株，并在 14 个不同的大豆品种上进行了下胚轴接种，这些品种都携带单个基因或没有抗性基因。调查发现，与 1993 年至 1997 年在密歇根州进行的上一次调查相比，基因 1b、1k、3b 和 6 的有效性丧失。在密歇根州，鉴定出了 3a、3c 和 4 三个有效抗性基因用于管理疫霉。此外，还确定了常见种子处理杀菌剂抑制菌丝生长 50%（EC50）的有效浓度。没有对测试化学物质不敏感的疫霉菌分离株，乙肟菌胺、甲霜灵、唑菌酯和吡唑醚菌酯的平均 EC50 值分别为 2.60×10μg/ml、3.03×10μg/ml、2.88×10μg/ml 和 5.08×10μg/ml。结果表明，尽管基因有效性发生了重大变化，但种子处理仍然是该病早期管理的有效方法。
