However, there may be other mechanisms of antifungal action
for branched alkyl paraben, because the inhibitory activity of
3,3-dimethylbutyl paraben (10) against oxygen consumption was
less effective than its antifungal activity.
A. brassicicola is a necrotrophic fungal pathogen that causes
black leaf spot disease in many cruciferous crops including cabbage
(Brassica oleracea L.). Branched alkyl parabens were more effective
against A. brassicicola than against other plant pathogenic fungi.
Thus, we estimated the effect of alkyl parabens on A. brassicicola
infection of detached cabbage leaves. The infection test was performed
according to a previously described method, with slight
modifications.12,13 The results showed that paraben-treated plants
were more resistant to A. brassicicola than untreated plants
(Fig. 5A). Quantification of infection levels of A. brassicicola in the
plants was carried out by measuring the infective gene copy numbers
in the fungal genome by real-time PCR.14,15 Alkyl paraben
treatment reduced fungal genomic DNA levels in a dose-dependent
manner (Fig. 5B). These results indicate that alkyl parabens have
the potential to reduce crop losses due to A. brassicicola infection.
In this Letter, we demonstrated that alkyl parabens showed the
antifungal activity against plant fungal pathogens. In particular,
branched alkyl parabens (8–10) were more potent in inhibiting
fungal growth than the linear alkyl parabens with the similar
logP values. In addition, linear alkyl parabens inhibited oxygen
consumption, which was linked to the increase in the chain length