Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583.
Department of Plant Science and Landscape Architecture, University of Connecticut, Storrs, CT 06269.
Plant Dis. 2023 May;107(5):1310-1315. doi: 10.1094/PDIS-06-22-1318-SC. Epub 2023 May 8.
Alternaria leaf blight and head rot is an important disease of broccoli and other cole crops. With no resistant host varieties, fungicides are utilized to manage this disease. However, anecdotal evidence suggests that, in southeastern U.S. broccoli-producing states, there is a loss of disease control through the use of quinone outside inhibitor (QoI) fungicides. To understand why there is a reduced sensitivity to QoI fungicides in these states, we isolated spp. from symptomatic lesions on cole crops from Georgia and Virginia (two states with observations of loss of fungicide sensitivity) as well as New York (a state with no observations of loss of fungicide sensitivity). Using multilocus sequencing and phylogenetic analysis, we identified two species, and . Whereas was isolated in all states, was only isolated in Georgia. Next, we wanted to determine the sensitivity of these isolates to azoxystrobin-an active ingredient in some QoI fungicides-by estimating the effective concentration at which only 50% of spores germinate (EC). The EC of ranged from 0.01 to 0.17 ppm, whereas that of was 8.1 to 28.1 ppm. None of the known target-site mutations that confer resistance to QoI fungicides were identified during screening of either species. was first reported on the east coast of the United States in 2020 in South Carolina. The substantially higher EC value suggests that its emergence in the southeastern United States may play at least a part in the observed loss of disease control. However, further in planta and field studies are needed to thoroughly test this hypothesis.
链格孢叶斑病和头部腐烂是西兰花和其他十字花科作物的重要病害。由于没有抗性宿主品种，因此使用杀菌剂来防治这种疾病。然而，传闻证据表明，在美国东南部的西兰花种植州，由于使用了醌外抑制剂（QoI）杀菌剂，该病的防治效果丧失。为了了解为什么在这些州对 QoI 杀菌剂的敏感性降低，我们从佐治亚州和弗吉尼亚州（两个观察到杀菌剂敏感性丧失的州）以及纽约州（一个没有观察到杀菌剂敏感性丧失的州）的十字花科作物的症状性病变中分离出了 spp.。通过多位点测序和系统发育分析，我们鉴定出了两个种， 和 。虽然 在所有州都有分离，但 在佐治亚州仅分离到 。接下来，我们希望通过估计只有 50%孢子发芽的有效浓度（EC）来确定这些分离株对唑菌胺酯（一些 QoI 杀菌剂的有效成分）的敏感性。 的 EC 值范围为 0.01 至 0.17ppm，而 的 EC 值为 8.1 至 28.1ppm。在对两个物种进行筛选时，均未发现赋予对 QoI 杀菌剂抗性的已知靶标位点突变。 于 2020 年首次在美国东海岸的南卡罗来纳州报道。其明显更高的 EC 值表明，它在东南部美国的出现可能至少在一定程度上导致了观察到的疾病控制失效。然而，需要进一步进行室内和田间研究来彻底验证这一假设。
