The use of transmissible hypovirulence for the biological control of Ophiostoma, the causal agent of Dutch elm disease

美国榆树的自然种群和城市种群已经被荷兰榆树病（DED）的致病真菌蛇瘤属（Ophiostoma）摧毁。对这种病原体的控制主要是使用杀菌剂来阻止真菌的生长，或使用杀虫剂来控制昆虫媒介的传播，但这两种方法都不是很有效。一种有吸引力的替代使用化学农药或杀菌剂的方法是开发一种生物防治新乌尔米病的方法。这至少需要一种对真菌具有拮抗作用的药剂，这种药剂可以传播给田间现存的真菌种群，并且非常具体，以尽量减少脱靶效应。低毒力是病原体对其宿主的毒力下降，可能由许多原因引起，包括线粒体DNA突变、核基因组突变或分枝病毒的存在。我们打算通过开发一种利用工程dsRNA载体对DED进行生物控制的传染病控制，扩大传染性低毒力在真菌病原体管理中的应用。通过分枝病毒诱导低毒力可以很容易地应用于O. novoo -ulmi，因为加拿大西部疾病前沿的目标群体基本上由两个非常大的克隆组成，并且植物相容性障碍很少。我们已经确定了一种新的dsRNA有丝分裂病毒OnuMV1c的基因组序列，该病毒是从一株感染的新乌尔米原虫中分离出来的，并证明了它在菌株之间的传播。存在于细胞质中的部分病毒，已在密切相关的物种中被描述，预计可传播给O. novoo -ulmi。通过我们对O. novoo -ulmi基因组学的研究，我们已经确定了几个基因位点，这些基因位点被认为是致病性和真菌适应性的组成部分。我们打算通过插入特定于已鉴定的O. novo-ulmi基因位点的沉默RNA （siRNA）来选择性地下调对真菌生存至关重要的基因，从而开始重新设计病毒dsRNAs。RNAi工程低病毒的发展为许多真菌病原体的生物防治提供了一种新的途径。

Natural and urban populations of the American elm have been devastated by pathogenic fungi of the genus Ophiostoma, the causal agent of Dutch elm disease (DED). Control of this pathogen has focused on fungicides to stem the growth of the fungus or pesticides to control the spread of the insect vector however neither option has been very effective. An attractive alternative to the use of chemical pesticides or fungicides is the development of a biological control for O. novo-ulmi. This requires, at minimum, an agent that is antagonistic to the fungus, is transmissible to extant populations of the fungus in the field, and is very specific to minimize off-target effects. Hypovirulence is the decreased virulence of a pathogen towards its host and can result from many causes including mitochondrial DNA mutations, nuclear genome mutations or the presence of mycoviruses. We intend to extend the application of transmissible hypovirulence for the management of fungal pathogens by the development of a transmissible disease control using engineered dsRNA vectors for the biological control of DED. Induction of hypovirulence via mycoviruses could readily be applied to O. novo-ulmi as the target population at the western Canadian disease front is essentially composed of two very large clones and vegetative compatibility barriers are rare. We have determined the genome sequence of a new dsRNA mitovirus OnuMV1c isolated from an infected O. novo-ulmi at disease front and demonstrated its transmission between strains. Partitiviruses, which reside in the cytoplasm, have been described in closely related species and are expected to be transmissible to O. novo-ulmi. Through our work on the genomics of O. novo-ulmi we have identified several gene loci thought to be integral to pathogenicity and fungal fitness. We intend to embark on the re-engineering of viral dsRNAs by the insertion of silencing RNA (siRNA) specific to identified O. novo-ulmi gene loci to selectively down-regulate genes critical to fungal survival. The development of RNAi engineered hypoviruses could provide a new approach for biological control that would be applicable to many fungal pathogens.