1Department of Microbiology and Plant Pathology, University of California, Riverside, CA 92521.
2Department of Botany and Plant Sciences, University of California, Riverside, CA 92521.
Plant Dis. 2019 Aug;103(8):2024-2032. doi: 10.1094/PDIS-09-18-1698-RE. Epub 2019 Jun 27.
Phytophthora root rot (PRR), caused by , is the most destructive disease of avocado worldwide. In the United States, mefenoxam and phosphonate products are currently the only registered fungicides for managing avocado PRR. Four new Oomycota-specific and two registered fungicides, all with different modes of action, were evaluated. Seventy-one isolates of from avocado in California, most of them collected between 2009 to 2017, were tested for their in vitro sensitivity to the six fungicides. Baseline sensitivity ranges and mean values (in parentheses) of effective concentrations to inhibit mycelial growth by 50% (EC) for the new fungicides ethaboxam, fluopicolide, mandipropamid, and oxathiapiprolin were 0.017 to 0.069 μg/ml (0.035), 0.046 to 0.330 μg/ml (0.133), 0.003 to 0.011 μg/ml (0.005), and 0.0002 to 0.0007 μg/ml (0.0004), respectively. In comparison, the EC value range (mean) was 0.023 to 0.138 μg/ml (0.061) for mefenoxam and 12.9 to 361.2 μg/ml (81.5) for potassium phosphite. Greenhouse soil inoculation trials with 8-month-old Zutano seedlings and 10-month-old Dusa and PS.54 clonal rootstocks were conducted to assess the efficacy of these fungicides for managing PRR. Mefenoxam and potassium phosphite were effective treatments; however, oxathiapiprolin, fluopicolide, and mandipropamid were more effective. Ethaboxam was effective in reducing PRR on the rootstocks evaluated. Oxathiapiprolin reduced PRR incidence and pathogen population size in the soil by >90%, and plant shoot growth and root dry weight were significantly increased compared with the control; thus, oxathiapiprolin was one of the best treatments overall. The high activity and performance of these new fungicides supports their registrations on avocado for use in rotation and mixture programs, including with previously registered compounds, to reduce the risk of development and spread of resistance in pathogen populations.
疫霉根腐病（PRR）由 引起，是全世界鳄梨最具破坏性的疾病。在美国，目前只有灭蝇胺和膦酸盐产品被注册用于防治鳄梨 PRR。本研究评估了四种新的卵菌纲特异性杀菌剂和两种已注册杀菌剂，它们都具有不同的作用模式。对加利福尼亚州鳄梨中采集的 71 个分离物（大多数收集于 2009 年至 2017 年之间）进行了体外敏感性测试，以评估这六种杀菌剂的敏感性。新杀菌剂乙肟威、氟吡菌酰胺、双丙环虫酯和唑醚·噻唑膦的有效浓度抑制 50%菌丝生长的基线敏感性范围和平均值（括号内）分别为 0.017 至 0.069μg/ml（0.035）、0.046 至 0.330μg/ml（0.133）、0.003 至 0.011μg/ml（0.005）和 0.0002 至 0.0007μg/ml（0.0004）。相比之下，灭蝇胺的 EC 值范围（平均值）为 0.023 至 0.138μg/ml（0.061），而亚磷酸钾的 EC 值为 12.9 至 361.2μg/ml（81.5）。用 8 个月大的 Zutano 实生苗和 10 个月大的 Dusa 和 PS.54 无性系砧木进行温室土壤接种试验，以评估这些杀菌剂防治 PRR 的效果。灭蝇胺和亚磷酸钾是有效的处理方法；然而，唑醚·噻唑膦、氟吡菌酰胺和双丙环虫酯的效果更好。乙肟威在评估的砧木上可有效减轻 PRR。唑醚·噻唑膦可将 PRR 的发病率和土壤中病原菌的种群规模减少 90%以上，与对照相比，植物地上部分生长和根干重显著增加；因此，唑醚·噻唑膦是整体上最好的处理方法之一。这些新杀菌剂的高活性和性能支持它们在鳄梨上的注册，用于轮作和混配方案，包括与以前注册的化合物一起使用，以降低病原菌种群中抗药性发展和传播的风险。
