Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695.
Department of Crop and Soil Science, North Carolina State University, Raleigh, NC 27695.
Plant Dis. 2018 Feb;102(2):309-317. doi: 10.1094/PDIS-03-17-0339-RE. Epub 2017 Dec 18.
Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of resistance to P. nicotianae, designated as Wz, has been introgressed into Nicotiana tabacum from N. rustica. The Wz gene region confers high levels of resistance to all races, but has not been characterized. Our study found Wz-mediated resistance is most highly expressed in the roots, with only a slight reduction in stem-lesion size in Wz genotypes compared with susceptible controls. No substantial relationships were observed between initial inoculum levels and disease development on Wz genotypes, which is generally consistent with qualitative or complete resistance. Isolates of P. nicotianae adapted for five host generations on plants with the Wz gene caused higher disease severity than isolates adapted on Wz plants for only one host generation. Wz-adapted isolates did not exhibit increased aggressiveness on genotypes with other sources of partial resistance, suggesting pathogen adaptation was specific to the Wz gene. To reduce potential for pathogen population shifts with virulence on Wz genotypes, Wz should be combined with other resistance sources and rotation of varying black shank resistance mechanisms is also recommended.
黑胫病由烟草疫霉引起，是全球范围内影响烟草最重要的病害之一，主要通过利用宿主抗性进行防治。已经从普通烟草中导入了另一个对烟草疫霉具有抗性的基因 Wz，该基因源自普通黄花烟。Wz 基因区域赋予了对所有菌系的高水平抗性，但尚未进行特征描述。我们的研究发现，Wz 介导的抗性在根部表达最高，与易感对照相比，Wz 基因型的茎部病斑大小仅有轻微减少。在 Wz 基因型上，初始接种物水平与病害发展之间没有观察到实质性关系，这通常与定性或完全抗性一致。在具有 Wz 基因的植株上适应了五个宿主世代的烟草疫霉分离物比仅在 Wz 植株上适应了一个宿主世代的分离物引起更高的病害严重度。Wz 适应的分离物在具有其他部分抗性来源的基因型上没有表现出更高的侵袭性，这表明病原体的适应是针对 Wz 基因的特异性的。为了降低 Wz 基因型上病原体种群毒性变化的风险，应将 Wz 与其他抗性来源结合使用，同时建议轮换具有不同黑胫病抗性机制的品种。
