Control of the fungus Colletotrichum lindemuthianum in common bean plants by 2-methoxy-1,4-naphthoquinone

Abstract

The common bean is a crop of high economic importance in countries like Brazil, whose production is affected by the fungus Colletotrichum lindemuthianum, a causal agent of anthracnose. In view of this, twenty six naphthoquinones were synthesized and tested in liquid medium with C. lindemuthianum race 65 (LV134) or race 89 (LV228). After 72 h at 22 °C, under constant stirring, 2-methoxy-1,4-naphthoquinone (11) afforded the lowest value of minimum inhibitory concentration (MIC), which was equal to 15.6 μg/mL, while the commercial fungicide methyl thiophanate had MIC of 61 μg/mL. An aqueous Tween 80® solution of compound 11 was applied to plant leaves of the common bean. Seven days later, an aqueous suspension containing conidia of the race 65 (LV134) fungal strain was sprayed on the leaves. Methyl thiophanate (700 μg/mL) reduced the severity of anthracnose from 5.2 to 1.5, while compound 11 (179 μg/mL) reduced it to 3.5. Then, the most stable conformations of compound 11 were employed in a phamacophoric search in the Ligand Expo database. The amino acid sequences of the proteins complexed to ligands with Tanimoto scores equal to or greater than 0.5 were used in searches of the genomes of fungi. Only those enzymes with scores above 200 for searches carried out exclusively in the genomes of Colletotrichum spp. were selected for docking of compound 11 and inhibitors of the selected enzymes. As the affinities of compound 11 for the enzymes ferulic acid decarboxylase and flavocytochrome b2 were similar to the calculated values for inhibitors of these enzymes, these are probably the targets of compound 11 in C. lindemuthianum. Therefore, both compound 11 and such enzymes have the potential of being used in the development of more efficient chemical structures for the control of this fungus in the common bean.