Li Yonggang, Harris-Shultz Karen, Wang Hongliang, Wadl Phillip A, Ji Pingsheng
Agricultural College, Northeast Agricultural University, Harbin 150030, China; and Department of Plant Pathology, University of Georgia, Tifton 31794.
United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Crop Genetics and Breeding Research Unit, Tifton, GA 31793.
Plant Dis. 2017 Jul;101(7):1113-1118. doi: 10.1094/PDIS-01-17-0142-RE. Epub 2017 Apr 21.
Black shank, caused by Phytophthora nicotianae, occurs worldwide and is responsible for significant yield loss in tobacco production in Georgia. Management of the disease has primarily relied on utilization of tobacco cultivars with resistance to race 0 of the pathogen and application of the fungicide mefenoxam. Races of P. nicotianae currently prevalent in tobacco production in Georgia, their sensitivity to mefenoxam, and genetic diversity of the pathogen are largely unknown. To determine population structure and genetic diversity of the pathogen, simple sequence repeat (SSR) markers were used. Three races of P. nicotianae (races 0, 1, and 3) were isolated from infected tobacco plants, with race 3 identified in Georgia for the first time. The majority of isolates were identified as A2 mating type and all isolates were sensitive or intermediately sensitive to mefenoxam at 1 or 10 μg/ml, with effective concentration of mefenoxam for 50% mycelial growth reduction values ranging from <0.01 to 0.12 μg/ml. Bayesian and unweighted pair group method with arithmetic means analyses of 59 isolates using SSR markers grouped the isolates in two major groups. Group I contained 20 isolates, of which 19 isolates were collected from Berrien County. Group II contained 39 isolates collected from Bacon, Cook, Tift, and Toombs Counties as well as one sample from Berrien County. Genetic diversity of the isolates was associated with geographical location of collection, and isolates in group I were primarily (75%) race 1, whereas isolates in group II were primarily (69%) race 0. The presence of a single pathogen mating type at most of the locations implies low probability of sexual recombination that may have contributed to the low genetic diversity at a particular geographical location. Sensitivity of the isolates to mefenoxam indicates that the fungicide remains to be a potent tool for growers to combat the disease. Information generated in the study advances our knowledge about diversity and population structure of P. nicotianae, which facilitates development and implementation of effective disease management programs.
由烟草疫霉引起的黑胫病在全球范围内都有发生，在佐治亚州的烟草生产中导致了严重的产量损失。该病的防治主要依赖于利用对病原菌0号生理小种具有抗性的烟草品种以及施用甲霜灵杀菌剂。目前在佐治亚州烟草生产中普遍存在的烟草疫霉生理小种、它们对甲霜灵的敏感性以及病原菌的遗传多样性在很大程度上尚不清楚。为了确定病原菌的群体结构和遗传多样性，使用了简单序列重复（SSR）标记。从感染的烟草植株中分离出了烟草疫霉的3个生理小种（0号、1号和3号生理小种），其中3号生理小种是在佐治亚州首次发现。大多数分离株被鉴定为A2交配型，所有分离株在1或10μg/ml浓度下对甲霜灵敏感或中度敏感，甲霜灵使菌丝生长减少50%的有效浓度范围为<0.01至0.12μg/ml。使用SSR标记对59个分离株进行贝叶斯分析和算术平均数非加权配对组方法分析，将分离株分为两个主要组。第一组包含20个分离株，其中19个分离株来自贝里恩县。第二组包含从培根县、库克县、蒂夫特县和图姆斯县收集的39个分离株以及来自贝里恩县的一个样本。分离株的遗传多样性与采集地点的地理位置有关，第一组中的分离株主要（75%）为1号生理小种，而第二组中的分离株主要（69%）为0号生理小种。在大多数地点存在单一的病原菌交配型意味着有性重组的可能性较低，这可能导致了特定地理位置的遗传多样性较低。分离株对甲霜灵的敏感性表明，该杀菌剂仍然是种植者防治该病的有效工具。该研究产生的信息增进了我们对烟草疫霉多样性和群体结构的了解，这有助于制定和实施有效的病害管理计划。
