Extracts of Argemone mexicana L. Contain Antifungal Compounds for the In Vitro Control of Monilinia fructicola, Colletotrichum gloeosporioides, Fusarium oxysporum, and Sclerotinia sclerotiorum: Preliminary Evidence for Field Application

<i>Argemone mexicana</i> L. is considered a weed; however, it contains secondary metabolites that can control phytopathogenic fungi in vitro, with the potential to adapt its effectiveness in the field. In the present study, leaf extracts of <i>A. mexicana</i> (hexane and methanol) were prepared, and their chemical profiles were analyzed using gas chromatography-mass spectrometry (GC-MS). The in vitro antifungal activity of each extract was evaluated at different concentrations (500, 1000, 2000, 4000, and 8000 mg L^-1) against phytopathogens such as <i>Monilinia fructicola, Colletotrichum gloeosporioides, Fusarium oxysporum</i>, and <i>Sclerotinia sclerotiorum</i>. Based on their chemical profiles, 14 compounds were identified in the hexanic extract, and 11 compounds were identified in the methanolic extract. These compounds included those with antifungal activity, such as Benzene; 1.3-bis(1.1-dimethylethyl)-; pentanoic acid; 5-hydroxy-, 2,4-di-1-butylphenyl esters; 1,2,4-Triazol-4-amine; and N-(2-thienylmethyl). The hexanic extract demonstrated fungistatic activity on the four fungi tested, while the methanolic extract exhibited fungicidal activity against <i>C. gloeosporioides</i> and <i>F. oxysporum</i>. The results of the Probit analysis showed variations in the sensitivity of phytopathogenic fungi to the treatments evaluated. In <i>M. fructicola</i>, the hexane extract presented an EC₅₀ of 317,146 mg L^-1 and an EC₉₀ of 400,796 mg L^-1. For <i>C. gloeosporioides</i>, the EC₅₀ was 2676 mg L^-1 and the EC₉₀ was 888,177 mg L^-1, while in <i>F. oxysporum</i> an EC₅₀ of 34,274 mg L^-1 and an EC₉₀ of 1528 mg L^-1 were estimated. In the case of <i>S. sclerotiorum</i>, an EC₅₀ of 560 mg L^-1 and an EC₉₀ of 7776 mg L^-1 were obtained. Finally, for the commercial fungicide Captan^®, an EC₅₀ of 1.19 mg L^-1 and an EC₉₀ of 1.67 mg L^-1. These results suggest that extracts from <i>A. mexicana</i> could provide a natural alternative for the control of phytopathogenic fungi.