Antifungal potential and biosafety of native plants from the Brazilian Restinga ecosystem

Control of devastating phytopathogens such as the pineapple black rot causing-pathogen fungus, Thielaviopsis ethacetica, remains dependent on synthetic pesticides despite the detrimental implications of such conventional strategies. Here, attempting to identify and develop cleaner and more sustainable tools to control T. ethacetica, we evaluated the fungicidal potential through in vitro antimicrobial assays of Sideroxylon obtusifolium and Annona acutiflora leaf extracts. To ensure the sustainability of these alternative fungicide tools, we evaluated the toxicity and repellent effects of the most promising extracts against the non-target organism honey bees, Apis mellifera. Preliminary results by diffusion plating indicated bioactivity of the fractions ethyl acetate S. obtusifolium and butanol A. acutiflora on pineapple black rot causing-pathogen. The featured extract of S. obtusifolium reduced the growth rate by 90% and increased the lag phase of the target pathogen. The fungistatic action of both was observed at 6.25 mg/mL concentrations. Fungicidal activity in vitro was detected at 12.5 mg/mL (ethyl acetate S. obtusifolium) and 25.0 mg/mL (for butanol A. acutiflora). Polar extract A. acutiflora exerts selective fungistatic activity on pathogen conidia. Both highlight extracts did not kill A. mellifera foragers even when applied at concentrations as high as 10-fold the fungicidal concentration. Honeybee reduced their feeding activities when they had to feed on plant extract-contaminated diets and extracts from S. obtusifolium and repelled honeybees under free choice conditions. Our findings collectively showed that these plant extracts could be helpful alternative fungicide tools to be integrated into managing T. ethacetica infestations in many food and industrial crops.