Bacteriostatic and bactericidal potential of Aloe vera leaf against Erwinia amylovora and Xanthomonas arboricola pv. juglandis

Nowadays، biocontrol of plant pathogens is a priority to reduce environmental effects of chemical pesticide applications. In this regard، antimicrobial plant products are in the center of attention. In this study، the inhibitive potential of methanol، ethanol، acetone، and chloroform extracts of rind، gel، latex and whole leaf of Aloe vera was evaluated using agar diffusion disc method against Erwinia amylovora and Xanthomonas arboricola pv. juglandis. Also، bacteriostatic and bactericidal activities were tested by minimal inhibitive and bactericidal concentration methods. All leaf parts of A. vera had antibacterial potential against these bacteria except for latex. However، X. arboricola pv. juglandis was more sensitive to Aloe products than E. amylovora. Chloroform was not suitable solvent for releasing antibacterial substances from Aloe. Rind extracts had no bactericidal or bacteriostatic effects on E. amylovora but they were the most effective ones on X. arboricola pv. juglandis. Gel extracts had much more bactericidal potential on both bacteria. On the whole، 31 chemicals were identified using gas chromatography which 25 of them were found in latex. Some antibacterial substances such as cinnamic acid، tetradecanoid acid، 2-hydroxy propionate، sitosterol، carvone، lupeol، 1-heptanol، 2-propyle، 1،2- benzene di-carboxylic acid were found in different parts of A. vera leaf. The antibacterial activity of A. vera against the causal agents of apple and pear fire blight and walnut bacterial blight can be considered as a biocontrol potential in the future.