Efficacy of Argentinean propolis extracts on control of potato soft rot caused by Erwinia carotovora subsp.

Abstract

Erwinia carotovora subsp. cause the potato soft rot, which is a major disease in agriculture. Antibacterial agents currently applied on potato soft rot often offer a restricted control and have several disadvantages. Propolis has shown a wide range of antimicrobial activity, although its effect has not been investigated on E. carotovora subsp. In this work, we tested extracts from propolis samples of Northwest Argentina against E. carotovora subsp. Ethanolic propolis extracts (EPEs) from samples of Santiago del Estero province, particularly from sample 4 (EPE4), showed the highest antibacterial activity, which was associated with the highest content of flavonoids. 2',4'-Dihydroxychalcone, 2',4'-dihydroxy-3'-methoxychalcone, galangin, and pinocembrin were identified as antibacterial constituents of EPE4. 2',4'-Dihydroxychalcone showed an antibacterial activity (minimum inhibitory concentration, MIC = 0.3-1.2 μg gallic acid equivalents (GAE) mL-1 ; minimum bactericidal concentration, MBC = 0.6-4.8 μg GAE mL-1 ) lower than that of bacterimycin (MIC = 2.4-9.6 μg mL-1 ; MBC = 19.2-38.4 μg GAE mL-1 ) and streptocycline (MIC = 19.2-38.4 μg mL-1 ; MBC = 38.4-76.8 μg mL-1 ). Preventive assays on unwounded and wounded potatoes showed that their immersion in EPE4 containing 87.5 μg GAE mL-1 or streptocycline containing 40 μg mL-1 was equally effective in controlling potato soft rot, reducing the disease incidence by 64.6-67.0% (unwounded tubers) and 88.0-86.0% (wounded tubers) and the disease severity by 49.8-49.8% (unwounded tubers) and 54.5-68.5% (wounded tubers). Flavonoid-rich propolis extracts from Northwest Argentina efficiently reduced in vivo the incidence and severity of potato soft rot caused by E. carotovora subsp.