Abstract

Wasabi (Wasabia japonica (Miq.) Matsum) plants are grown over a period of 12–18 months for their valuable rhizomes, and pathogens infecting the rhizome are of economic importance for producers. During 2016 and 2017, symptoms of wilting and internal vascular blackening of rhizomes were observed in two greenhouses in British Columbia, with disease incidence in the range of 5–10%. Isolates recovered from diseased tissues were examined morphologically and a majority (70%) resembled a Verticillium species. Molecular analysis using PCR of the ITS1-ITS2 region of rDNA and a portion of the actin gene identified the isolates as V. isaacii Inderb. R.M. Bostock, R.M. Davis & Subbarao. The optimal temperature for growth of V. isaacii on potato dextrose agar was 20°C and a distinct yellow pigment was produced, which is characteristic of species in the clade Flavexudans. Inoculation of detached wounded wasabi tissues with V. isaacii produced blackening symptoms and chlorosis on leaves. Black streaks developed on petioles and internal blackening of rhizomes was also observed. Plants inoculated in the greenhouse by immersing wounded roots in a spore suspension of V. isaacii developed a reduced root system compared with control plants. Blackening of the rhizome tissue was observed after three months. Differences were observed in pathogenicity between V. isaacii isolates. We demonstrate for the first time that V. isaacii is the cause of wilting and vascular blackening on wasabi plants. It is considered a weak pathogen, only affecting wounded tissues with symptoms developing after an extended time following inoculation.

摘要

芥末 ( Wasabia japonica (Miq.) Matsum ) 植物因其有价值的根茎而生长 12-18 个月，感染根茎的病原体对生产者具有重要的经济意义。2016年和2017年，不列颠哥伦比亚省的两个温室中观察到根茎枯萎和内部维管变黑的症状，发病率在5-10%之间。从患病组织中回收的分离株进行了形态学检查，大多数 (70%) 类似于轮枝菌属物种。使用 rDNA 的 ITS1-ITS2 区域和部分肌动蛋白基因的 PCR 进行分子分析，将分离物鉴定为五角星形弧菌Inderb。RM Bostock、RM Davis 和 Subbarao。V. isaacii生长的最适温度在马铃薯葡萄糖琼脂上的温度为 20°C，产生了明显的黄色色素，这是 Flavexudans 进化枝中物种的特征。将分离的受伤芥末组织接种到五味子中会在叶子上产生变黑症状和萎黄病。叶柄上出现黑色条纹，根茎内部变黑。与对照植物相比，通过将受伤的根浸泡在五角星孢子悬浮液中而在温室中接种的植物的根系减少了。三个月后观察到根茎组织变黑。V. isaacii分离株之间的致病性存在差异。我们首次证明V. isaacii是芥末植物萎蔫和血管变黑的原因。它被认为是一种弱病原体，仅影响受伤组织，并在接种后长时间出现症状。