Extracts of Agrito (Rhus Microphylla Engelm. Ex A. Gray) for the control of plant pathogenic Fungi

Abstract

The greatest losses in crops in the field and postharvest stage, are mostly produced by the attack of fungi. Fusarium oxysporum and Corynespora cassiicola are two devastating plant pathogenic fungi that infect several crops (e.g. tomato and cucumber). The conventional agriculture uses chemical pesticides; however, a large majority of crops are generating resistance, in addition to having a negative impact on health and the environment. The use of plant extracts has emerged as a natural alternative within the framework of organic agriculture, highlighting the plants of the Mexican Semidesert. In this context, the properties of agrito (Rhus microphylla), a plant used in the traditional medicine, have not been studied. Thus, the objectives of this work were: (1) to evaluate the antifungal activity in vitro of aqueous (AE), ethanol (EE), and hydro-alcohol (HAE) extracts of berries of R. microphylla on F. oxysporum and C. cassiicola; and (2) to characterize the extracts in the terms of total phenolic compounds (TPC) by Folin Ciocalteu and ultra-high-performance liquid chromatography (UHPLC) methods, and antioxidant activity expressed as the concentration required to obtain a 50% of inhibition of radical scavenging activity (IC50). The EE showed the highest (p<0.05) content of TPC (201.6 +/- 3.3 mg gallic acid (GA) g-1 extract), characterized by the presence of gallic acid (321.9 +/- 4.0 mg L-1) and p-cumaric acid + epicatechin (42.2 +/- 2.9 mg L-1); followed by HAE (151.0 +/- 3.9 mg GA g-1 extract), which mainly contains gallic acid and p-cumaric acid + epicatechin (98.6 +/- 4.4 and 78.2 +/- 1.5 mg L-1, respectively); and AE (146.8 +/- 0.1 mg GA g-1 extract), in which gallic acid was detected at a concentration of 203.2 +/- 0.7 mg L-1. However, EE and AE did not present significant differences in the antioxidant activity, as both showed an IC50 of 0.1 +/- 0.0 mg mL-1 , while for HAE the IC50 value was 0.2 +/- 0.0 mg mL-1. These results are interesting and support the antifungal behavior of the extracts. For both fungi, the antifungal activity was concentration-dependent and varied according to the fungus genera, being the EE that had a significant inhibition of 100% growth of both fungi from the concentration of 2500 mg L-1. The HAE allowed an inhibition about 60% also at 2500 mg L-1 for both fungi, and 100% of inhibition of C. cassiicola at 3000 mg L-1. The AE exhibited the lowest (p<0.05) antifungal effect with inhibition values of 20.8 +/- 3.4 and 62.8 +/- 1.5% at 3000 mg L-1 for F. oxysporum and C. cassiicola, respectively. The EE and HAE of berries of R. microphylla are promising as a natural alternative to control phytopathogenic fungi in crops of commercial importance.