1 Ottawa Research and Development Centre, Agriculture and Agri-Food, Ottawa ON, K1A 0C6, Canada.
2 Ontario Ministry of Agriculture, Food and Rural Affairs, ON, N0P 2C0, Canada.
Plant Dis. 2019 Jul;103(7):1450-1457. doi: 10.1094/PDIS-06-18-0951-SR. Epub 2019 May 20.
Northern corn leaf blight (NCLB) caused by is the most common and economically significant fungal leaf disease of corn in Ontario, Canada. During the past 10 years in Ontario, severity and incidence of NCLB have increased, possibly owing to the appearance of new races. Several races have been identified in various parts of the world; however, information on occurrence and distribution of races in Ontario is lacking. In the current study, 677 single conidial isolates of were isolated from 687 symptomatic leaf samples collected between 2012 and 2016. These isolates were evaluated for pathogenicity on six corn differential inbreds (A619, A619, A619, A619, A632, and H102) under controlled environmental conditions and then grouped into 17 physiological races (0, 1, 2, 3, M, N, 12, 1M, 1N, 3M, 13M, 12N, 13N, 1MN, 12MN, 13MN, 123MN) based on the reaction of the inbreds to infection (resistant or susceptible). Four races (0, 1M, 1N, and 1MN) were most frequent, with an isolation frequency of 13, 10, 12, and 41%, respectively. Seventy-six percent of the isolates were virulent on more than one resistance gene, with 2.4% (16 isolates) virulent on all five resistance genes used in this study. Further analysis of the distribution of races in four regions over the years revealed that the occurrence and distribution of the races changed with time in Ontario. Overall, the frequency of virulence of the 677 isolates screened on the differentials with resistance genes , , , , and varied from 6 to 81% ( 81%, 6%, 12%, 64%, and 64%). Virulent isolates produced fewer lesions on the differential, and smaller lesions that were slower and having less sporulation on the differential, compared with infection of the differentials with , , and resistance genes. Virulence frequency also changed within the four geographical regions of Ontario, with fewer isolates virulent on all resistance genes in eastern Ontario compared with southern and western Ontario. Isolates from southern Ontario had greater virulence frequency against and , whereas isolates from western Ontario were more frequently virulent on and The information generated in this study on the distribution of races in Ontario corn will help growers to select appropriate hybrids with required resistance genes and will assist seed companies in deploying resistance genes in corn hybrids across the province or within a particular region.
加拿大安大略省，由 引起的北方玉米叶枯病（NCLB）是玉米上最常见且经济上最重要的真菌叶部病害。在过去的 10 年中，NCLB 的严重程度和发生率有所增加，这可能是由于新菌株的出现。世界上已经鉴定出了几个菌株；然而，关于安大略省菌株的发生和分布的信息却很缺乏。在本研究中，从 2012 年至 2016 年间采集的 687 份有症状的叶片样本中，分离出了 677 株 单孢分离物。这些分离物在受控环境条件下对 6 种玉米鉴别品种（A619、A619、A619、A619、A632 和 H102）的致病性进行了评估，然后根据鉴别品种对感染的反应（抗性或敏感）分为 17 个生理小种（0、1、2、3、M、N、12、1M、1N、3M、13M、12N、13N、1MN、12MN、13MN、123MN）。4 个小种（0、1M、1N 和 1MN）最为常见，其分离频率分别为 13%、10%、12%和 41%。76%的分离物对超过一个 抗性基因具有毒性，其中 2.4%（16 个分离物）对本研究中使用的所有 5 个 抗性基因均具有毒性。对多年来四个地区的小种分布的进一步分析表明，安大略省的小种发生和分布随时间而变化。总体而言，677 个分离物在具有抗性基因的鉴别品种上的毒性频率从 6%到 81%不等（81%、6%、12%、64%和 64%）。与感染具有 、 、 和 抗性基因的鉴别品种相比，毒性分离物在鉴别品种上产生的病变更少，且病变更小、生长速度更慢、产孢量更少。在安大略省的四个地理区域内，毒性频率也发生了变化，与安大略省南部和西部相比，安大略省东部具有所有抗性基因的毒性分离物较少。来自安大略省南部的分离物对 和 具有更高的毒性频率，而来自安大略省西部的分离物对 和 具有更高的毒性频率。本研究中关于安大略省玉米 小种分布的信息将有助于种植者选择具有所需抗性基因的合适杂交种，并有助于种子公司在全省或特定地区部署玉米杂交种中的抗性基因。
