Albugo-induced camalexin is biologically unavailable to Botrytis cinerea.
B. cinerea gives increased disease symptoms on Albugo-infected tissue. Leaves of water-sprayed or AlNc14-infected Col-0 Arabidopsis (11 dpi) were inoculated with 2.5 × 105 spores per mL of B. cinerea B05.10 or camalexin sensitive ΔBcatrB4 mutant, and lesion diameters were measured at 2 dpi. Bars represent mean lesion diameter ± SE of three independent biological replicates with between 7 and 11 technical replicates per biological replicate (n = 28). Different letters indicate significant differences between treatments at P < 0.01 (Two-way ANOVA with Tukey’s honest significance difference). b Camalexin accumulates in plants infected by Albugo and B. cinerea, either alone or together. High-performance liquid chromatography (HPLC) analysis of mock or AlNc14-infected Col-0 tissue (12 dpi), 26 hours post mock or B. cinerea B05.10 inoculation by spraying (2.5 × 105 spores per mL). Open circles and bars denote mean camalexin content per mg of fresh weight ± SE of three independent biological replicates with six technical replicates per biological replicate. Closed, black circles denote individual data points. Asterisks indicate significant differences from mock treated plants (12 days post water spraying, 26 hours post inoculation) at P < 0.001 (Generalized linear model (GLM)). c
B. cinerea detects less available camalexin in Albugo-infected tissue. Leaves of mock or AlNc14-infected Arabidopsis (11 dpi) were drop inoculated with 2.5 × 105 spores per mL of B. cinerea strains OliCGUS (constitutive GUS expression) or BcatBp803GUS-7 (camalexin inducible GUS expression). Leaves were stained with X-gluc at 2 dpi and the percentage of infection sites showing staining determined. Bars represent mean ± SE three independent biological replicates with between two and four technical replicates per biological replicate (bars left to right n = 5, 8, 7, 10, 5, 8). Different letters indicate significant differences P < 0.05 (Three-way ANOVA, Tukey’s honest significant difference test)