Extracts and phenolic compounds from Zuccagnia punctata as fungicide seed protectants for corn

Abstract

The ethanolic leaf extract (TZP) of Zuccagnia punctata, its ethereal fraction (Eet), 2′,4′-dihydroxychalcone (DC), 2′,4′-dihydroxy-3′-methoxychalcone (DMC) and 7-hydroxy-3′,4′-dimethoxyflavone (HF) were evaluated as fungicide seed protectants on corn. Microdilution assays on a set of Fusarium strains showed minimum inhibitory concentrations (MICs) of 400–800 μg mL−1 (TZP), 50–100 μg mL−1 (Eet), 25–50 μg mL−1 (DC), 50–100 μg mL−1 (DMC) and 200–400 μg mL−1 (HF), with minimum fungicidal concentration (MFC)/MIC = 1. Suspensions of TZP, Eet, DC and DMC at MIC × 20 incorporated to the grains at rates of 1920, 240, 120 and 240 mg dry matter kg−1 of grain, respectively, increased the elongation of the primary roots (24–44%) and the number of seminal roots (44–50%). TZP also increased the number of secondary roots. HF was phytotoxic. Suspensions of TZP, Eet, DC and DMC suppressed the endogenous grain mycoflora at levels similar to those recorded for a thiram + carbendazim-based fungicide. Grains treated with TZP (1920 mg kg−1), Eet (240 mg kg−1), DC (120 mg kg−1) and DMC (240 mg kg−1) stimulated the growth of the seedling root system both because of fungal suppression and hormetic effects in greenhouse curative and preventive assays against Fusarium verticillioides on a sand/soil substrate. Eet and its chalcones also reduced the severity of seedling blight more than the thiram + carbendazim-based fungicide in preventive assays and led to the same disease severity observed for the fungicide treatment in the curative assays. Our results show that Eet and its chalcones not only were effective seed protectants against F. verticillioides and other seedborne fungi, but also improved the early performance of maize seedlings.