Thomas Anna, Carbone Ignazio, Lebeda Aleš, Ojiambo Peter S
First, second, and fourth authors: Center for Integrated Fungal Research, Department of Entomology and Plant Pathology, North Carolina State University, Raleigh 27695; and third author: Department of Botany, Palacký University, 78371 Olomouc, Czech Republic.
Phytopathology. 2017 Jun;107(6):777-785. doi: 10.1094/PHYTO-07-16-0277-R. Epub 2017 Apr 12.
Cucurbit downy mildew (CDM), caused by the obligate oomycete Pseudoperonospora cubensis, has resurged around the world during the past three decades. A new pathotype or genetic recombinant of P. cubensis have been suggested as possible reasons for the resurgence of CDM in the United States in 2004. In total, 22 isolates collected between 2004 and 2014, mainly in the eastern United States, were tested for their compatibility with a set of 15 cucurbit host types. The virulence structure within these isolates was evaluated on a set of 12 differential genotypes from eight genera. All isolates were highly compatible with the susceptible cultivar of Cucumis sativus, whereas the least compatibility was observed with Luffa cylindrica and Momordica charantia. Based on the compatibility with the differential host set, five pathotypes (1, 3, 4, 5, and 6) were identified among the 22 isolates examined. Pathotypes 1 and 3 had not been previously described in the United States and isolates of these two new pathotypes were also compatible with 'Poinsett 76', a cultivar of C. sativus known to be resistant to CDM prior to 2004. Virulence within the pathogen population was expressed based on virulence factors, virulence phenotypes, and virulence complexity. The number of virulence factors ranged from two to eight, indicating a complex virulence structure, with 77% of the isolates having five to eight virulence factors. Thirteen virulence phenotypes were identified; the mean number of virulence factors per isolate and mean number of virulence factors per virulence phenotype was 5.05 and 5.23, respectively, indicating that complex isolates and phenotypes contributed equally to the complex virulence structure of P. cubensis. Gleason and Shannon indices of diversity were 3.88 and 2.32, respectively, indicating a diverse virulence structure of P. cubensis within the United States population. The diverse virulence and high virulence complexity within the pathogen population indicate that host resistance alone in available cucurbit cultivars will not be effective to control CDM. An integrated approach involving a combination of fungicide application and introduction of cultivars with new resistance genes will be required for effective management of CDM.
由专性卵菌古巴假霜霉（Pseudoperonospora cubensis）引起的葫芦科霜霉病（CDM）在过去三十年里在全球范围内再度流行。一种新的古巴假霜霉致病型或基因重组体被认为是2004年美国葫芦科霜霉病再度流行的可能原因。总共对2004年至2014年间收集的22个分离株进行了测试，这些分离株主要来自美国东部，检测它们与一组15种葫芦科寄主类型的亲和性。在一组来自8个属的12个鉴别基因型上评估了这些分离株的毒力结构。所有分离株与黄瓜的感病品种高度亲和，而与丝瓜和苦瓜的亲和性最低。根据与鉴别寄主组的亲和性，在检测的22个分离株中鉴定出了5种致病型（1、3、4、5和6）。致病型1和3以前在美国未曾描述过，这两种新致病型的分离株也与‘波因塞特76’亲和，‘波因塞特76’是黄瓜的一个品种，在2004年之前已知对葫芦科霜霉病具有抗性。病原菌群体内的毒力根据毒力因子、毒力表型和毒力复杂性来表达。毒力因子的数量从2个到8个不等，表明毒力结构复杂，77%的分离株具有5到8个毒力因子。鉴定出了13种毒力表型；每个分离株的毒力因子平均数和每个毒力表型的毒力因子平均数分别为5.05和5.23，这表明复杂的分离株和表型对古巴假霜霉复杂的毒力结构贡献相同。多样性的格莱森指数和香农指数分别为3.88和2.32，表明在美国群体中古古巴假霜霉具有多样的毒力结构。病原菌群体内多样的毒力和高毒力复杂性表明，仅靠现有葫芦科品种中的寄主抗性不足以有效控制葫芦科霜霉病。有效的葫芦科霜霉病管理需要综合采用杀菌剂施用和引入具有新抗性基因的品种。
