In vitro sensitivity of Botrytis cinerea to anthraquinone and anthrahydroquinone derivatives

The effect on mycelial growth of the fungus Botrytis cinerea of a set of structurally related tricyclic hydroquinones [9,10-dihydroxy-4,4-dimethyl-2,3,5,8-tetrahydroantracen-1(4H)-one and 9,10-dihydroxy-4,4-dimethyl-5,8-dihydroanthracen-1(4H)-one derivatives] and tricyclic quinones [4,4-dimethylanthracen-1,9,10(4H)-trione derivatives] was studied. In general, the anthraquinones presented higher activity than the anthrahydroquinones. Anthraquinone and anthrahydroquinone derivatives with methyl groups on the A ring showed higher antifungal activity than the unsubstituted ones, 4,4,6,7-tetramethyl-(4H)-anthracene-1,9,10-trione being the most active compound of this set. The presence of a polar group such as hydroxymethyl reduced the activity. The effect of two anthrahydroquinones and two anthraquinones on the conidia germination of the fungus was also determined. Anthrahydroquinones did not affect the germination. The most active compound was 4,4-dimethylanthracene-1,9,10(4H)-trione, with 100% inhibition of germination at 7 h of incubation. These results again suggest that the structure of the anthraquinones is important in exerting an antifungal effect on B. cinerea. Furthermore, possible mechanisms of action of compound 4,4-dimethylanthracene-1,9,10(4H)-trione were studied. This compound did not produce lipoperoxidation of membrane and did not induce the formation of oxygen reactive species, but it was able to permeabilize the plasmatic membrane of B. cinerea, increasing the phosphorus concentration in the intracellular medium.