Department of Crop Sciences, University of Illinois, Urbana, 61801.
Plant Dis. 2018 Feb;102(2):292-299. doi: 10.1094/PDIS-01-17-0128-RE. Epub 2017 Dec 18.
Northern leaf blight (NLB) of corn, caused by Exserohilum turcicum, is a foliar disease common across corn production regions of the world, including those in the north central United States. Previous race population distribution studies identified five physiological races present in the United States, prior to 1995. For this study, 156 E. turcicum isolates were screened on corn differential lines containing Ht1, Ht2, Ht3, Htm1, and Htn1 resistance genes. Isolates were collected from fields in Iowa, Illinois, Indiana, Minnesota, North Carolina, Ohio, and Wisconsin, which included 143 isolates collected between 2007 and 2014 and 13 isolates collected between 1979 and 1985. Twenty different physiological races were observed based on the symptom response of the differential corn lines. E. turcicum race 0, 1, and 1mn were the most prevalent races, comprising 21, 27, and 13% of the 156 isolates, respectively. Race populations were diverse within states and years. Virulence to multiple Ht resistance genes within individual isolates was observed in 47% of those tested, with 3% of the isolates conferring virulence to all Ht resistance genes. Virulence to the Ht1, Ht2, Ht3, Htm1, and Htn1 resistance genes was present in 64, 20, 18, 32, and 27% of the E. turcicum isolates, respectively. Virulence to Ht resistance genes was fairly evenly distributed across states, in isolates collected after 2008. Virulence to Ht2, Ht3, Htm1, and Htn1 decreased after 2010. Variations in race population diversity are difficult to explain without knowing the level of selection pressure present in fields, and information regarding Ht resistance gene deployment in commercial varieties is not publicly available. Although virulence was observed against all Ht resistance genes, qualitative Ht resistance genes could be used in conjunction with quantitative resistance to increase NLB control.
玉米北方叶枯病（NLB）由突脐蠕孢菌（Exserohilum turcicum）引起，是一种叶片病害，普遍存在于世界各地的玉米种植区，包括美国中北部地区。在 1995 年之前，先前的病原菌群体分布研究确定了美国存在的五个生理小种。在这项研究中，对含有 Ht1、Ht2、Ht3、Htm1 和 Htn1 抗性基因的玉米鉴别系上的 156 个突脐蠕孢菌分离物进行了筛选。分离物来自爱荷华州、伊利诺伊州、印第安纳州、明尼苏达州、北卡罗来纳州、俄亥俄州和威斯康星州的田间，其中包括 2007 年至 2014 年采集的 143 个分离物和 1979 年至 1985 年采集的 13 个分离物。根据鉴别玉米品系的症状反应，观察到了 20 种不同的生理小种。突脐蠕孢菌小种 0、1 和 1mn 是最普遍的小种，分别占 156 个分离物的 21%、27%和 13%。在不同年份和不同州内，种群多样性丰富。在 47%的受检个体中观察到了对多个 Ht 抗性基因的毒性，其中 3%的分离物赋予了对所有 Ht 抗性基因的毒性。对 Ht1、Ht2、Ht3、Htm1 和 Htn1 抗性基因的毒性分别存在于 64%、20%、18%、32%和 27%的突脐蠕孢菌分离物中。在 2008 年后采集的分离物中，突脐蠕孢菌对 Ht 抗性基因的毒性相当均匀地分布在各州。2010 年后，突脐蠕孢菌对 Ht2、Ht3、Htm1 和 Htn1 的毒性降低。如果不知道田间存在的选择压力水平，就很难解释种群多样性的变化，而且关于商业品种中 Ht 抗性基因部署的信息也没有公开。尽管观察到了对所有 Ht 抗性基因的毒性，但定性的 Ht 抗性基因可以与数量抗性结合使用，以增加 NLB 的控制效果。
