Although
Brassica rapa (
B. rapa) is vital in agricultural production and vulnerable to the pathogen
Plasmodiophora, the intracellular water–nutrient metabolism and immunoregulation of
Plasmodiophora infection in
B. rapa leaves remain unclear. This study aimed to analyze the responsive mechanisms of
Plasmodiophora-infected
B. rapa using rapid detection technology. Six soil groups planted with Yangtze No. 5
B. rapa were inoculated with varying
Plasmodiophora concentrations (from 0 to 10 × 10
9 spores/mL). The results showed that at the highest infection concentration (PWB5, 10 × 10
9 spores/mL) of
B. rapa leaves, the plant electrophysiological parameters showed the intracellular water-holding capacity (IWHC), the intracellular water use efficiency (IWUE), and the intracellular water translocation rate (IWTR) declined by 41.99–68.86%. The unit for translocation of nutrients (UNF) increased by 52.83%, whereas the nutrient translocation rate (NTR), the nutrient translocation capacity (NTC), the nutrient active translocation (NAT) value, and the nutrient active translocation capacity (NAC) decreased by 52.40–77.68%. The cellular energy metabolism decreased with worsening
Plasmodiophora infection, in which the units for cellular energy metabolism (∆G
E) and cellular energy metabolism (∆G) of the leaves decreased by 44.21% and 78.14% in PWB5, respectively. Typically, based on distribution of B-type dielectric substance transfer percentage (BPn), we found PWB4 (8 × 10
9 spores/mL) was the maximal immune response concentration, as evidenced by a maximal BPn
R (B-type dielectric substance transfer percentage based on resistance), with increasing lignin and cork deposition to enhance immunity, and a minimum BPn
Xc (B-type dielectric substance transfer percentage based on capacitive reactance), with a decreasing quantity of surface proteins in the
B. rapa leaves. This study suggests plant electrophysiological parameters could characterize intracellular water–nutrient metabolism and immunoregulation of
B. rapa leaves under various
Plasmodiophora infection concentrations, offering a dynamic detection method for agricultural disease management.
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