To generate information on variability in the pathogen causing white rust disease in Brassica species and their ability to infect Brassica juncea genotypes, thirteen isolates of Albugo candida infecting B. juncea and one isolate of Wilsonia bliti infecting Amaranthus blitum were collected from different rapeseed-mustard growing regions of India. These isolates were characterized based on different morphological data (sporangial shape and size; shape, size, and color of the pustule) and molecular data (cytochrome c oxidase subunit II (COX2) of mtDNA and internal transcribed spacer (ITS) region of rDNA). All the sporangia were globose or spherical to ellipsoidal with a size ranging from 199.01 μm2 to 357.23 μm2. White to creamy colored pustules were observed with a diameter ranging from 0.5–3.0 mm. Sequence analysis revealed that the Indian isolates of A. candida collected from B. juncea showed close identity with the Korean isolates infecting B. juncea. W. blilti isolate collected from A. blitum form a distinct clade with A. amaranthi infecting Amaranthus spinosus from Korea. Further, the pathogenic reaction of ten A. candida isolates was recorded on thirty genotypes of B. juncea that exhibited differential responses to the tested isolates. The three genotypes, PDZ-3, Pusa Karishma, and Donskaja were found to be resistant against all the ten isolates, which can further be used as a resistance source. PDZ-2 genotype was found to be susceptible only against the Ac-Hr isolate while the genotype BioYSR shows a susceptible reaction against Ac-Skn and Ac-Wltn isolates only. This set of thirty genotypes was able to differentiate the ten isolates of A. candida into four physiological races (AcRBj1 to AcRBj4) based on the disease reaction. The information generated through this study will be helpful for further study on identification and molecular mapping of resistance gene(s), their deployment over time and space, and, thus, better management of white rust disease in B. juncea.

中文翻译：

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在印度感染芥菜基因型的白念珠菌分离株的形态分子变异性和宿主反应性

为了获得有关引起芸苔属植物白锈病的病原体变异性及其感染芥菜基因型的能力的信息，从不同的油菜籽芥菜种植中收集了 13 株感染芥菜的 Albugo candida 和一种感染 Amaranthus blitu 的 Wilsonia bliti 分离株印度的地区。根据不同的形态学数据（孢子囊的形状和大小；脓疱的形状、大小和颜色）和分子数据（mtDNA 的细胞色素 c 氧化酶亚基 II (COX2) 和 rDNA 的内部转录间隔区 (ITS) 区域）对这些分离株进行表征. 孢子囊均为球状或球状至椭圆形，大小199.01～357.23μm2。观察到直径为 0.5-3.0 毫米的白色至奶油色脓疱。序列分析表明，从芥菜中收集的印度念珠菌分离株与感染芥菜的韩国分离株表现出密切的同一性。从 A. blitum 收集的 W. blilti 分离物与 A. amaranthi 感染来自韩国的 Amaranthus spinosus 形成一个独特的进化枝。此外，十个念珠菌分离株的致病反应被记录在 30 种芥菜基因型上，这些基因型对测试的分离株表现出不同的反应。发现 PDZ-3、Pusa Karishma 和 Donskaja 三个基因型对所有十个分离株都具有抗性，可进一步用作抗性源。发现 PDZ-2 基因型仅对 Ac-Hr 分离株敏感，而基因型 BioYSR 显示仅对 Ac-Skn 和 Ac-Wltn 分离株敏感。这组三十个基因型能够根据疾病反应将念珠菌的十个分离株区分为四个生理种族（AcRBj1 到 AcRBj4）。通过本研究产生的信息将有助于进一步研究抗性基因的鉴定和分子图谱及其在时间和空间的部署，从而更好地管理芥菜白锈病。