Table_1_Histopathology of the Plasmodiophora brassicae-Chinese Cabbage Interaction in Hosts Carrying Different Sources of Resistance.DOCX

Clubroot is a serious soil-borne disease of crucifers caused by the obligate parasite Plasmodiophora brassicae. The genetic basis and histopathology of clubroot resistance in two Chinese cabbage (Brassica rapa ssp. pekinensis) inbred lines Bap055 and Bap246, challenged with pathotype 4 of P. brassicae, was evaluated. The Chinese cabbage cultivar “Juxin” served as a susceptible check. The resistance in Bap055 was found to be controlled by the CRa gene, while resistance in Bap246 fit a model of control by unknown recessive gene. Infection of the roots by P. brassicae was examined by inverted microscopy. Despite their resistance, primary and secondary infection were observed to occur in Bap055 and Bap246. Primary infection was detected at 2 days post-inoculation (DPI) in “Juxin,” at 4 DPI in Bap055, and at 6 DPI in Bap246. Infection occurred most quickly on “Juxin,” with 60% of the root hairs infected at 10 DPI, followed by Bap055 (31% of the root hairs infected at 12 DPI) and Bap246 (20% of the root hairs infected at 14 DPI). Secondary infection of “Juxin” was first observed at 8 DPI, while in Bap055 and Bap246, secondary infection was first observed at 10 DPI. At 14 DPI, the percentage of cortical infection in “Juxin,” Bap055 and Bap246 was 93.3, 20.0, and 11.1%, respectively. Although cortical infection was more widespread in Bap055 than in Bap246, secondary infection in both of these hosts was restricted relative to the susceptible check, and the vascular system remained intact. A large number of binucleate secondary plasmodia were observed in “Juxin” and the vascular system was disrupted at 16 DPI; in Bap055 and Bap246, only a few secondary plasmodia were visible, with no binucleate secondary plasmodia. The defense mechanisms and expression of resistance appears to differ between Chinese cabbage cultivars carrying different sources of resistance.

根肿病是由专性寄生菌芸苔根肿菌（Plasmodiophora brassicae）引起的一种严重十字花科土传病害。本研究针对两个大白菜（Brassica rapa ssp. pekinensis）自交系Bap055与Bap246，接种芸苔根肿菌4号致病型，解析其抗根肿病的遗传基础与组织病理学特征，并以大白菜品种"聚鑫"作为感病对照。经鉴定，Bap055的抗病性由CRa基因调控，而Bap246的抗病性则符合未知隐性基因控制的遗传模型。本研究通过倒置显微镜观察芸苔根肿菌对寄主根系的侵染过程。尽管两个自交系均表现出抗病性，但仍可在其根系中观察到初生侵染与次生侵染事件。"聚鑫"的初生侵染于接种后2天（days post-inoculation, DPI）被检测到，Bap055为4 DPI，Bap246为6 DPI。侵染进程最快的为"聚鑫"，至10 DPI时已有60%的根毛被侵染；其次为Bap055，12 DPI时根毛侵染率达31%；最慢的是Bap246，14 DPI时根毛侵染率仅为20%。"聚鑫"的次生侵染首次出现于8 DPI，而Bap055与Bap246的次生侵染均首次出现于10 DPI。至14 DPI时，"聚鑫"、Bap055与Bap246的皮层侵染率分别为93.3%、20.0%与11.1%。尽管Bap055的皮层侵染范围较Bap246更广，但相较于感病对照，两个自交系的次生侵染均受到显著抑制，且寄主维管束系统保持完整。至16 DPI时，"聚鑫"根系中可观察到大量双核次生原生质团，且维管束系统被破坏；而Bap055与Bap246中仅可见少量次生原生质团，未发现双核次生原生质团。本研究结果表明，携带不同抗病基因源的大白菜品种，其抗病防御机制与抗性表达模式存在显著差异。