Antimicrobial Activity of Different Molecular Weight Chitosans Produced from Shrimp Shells Against Different Plant Pathogens

The effect of ten chitosan products, obtained from shrimp shells, with a viscosity-average molecular weight ranged from 22 to 387 kDa on antimicrobial activity against different plant pathogenic bacteria and fungi, was investigated in vitro and compared with standard high molecular weight chitosan (846 kDa). The antibacterial activity was estimated by broth microdilution and agar dilution techniques as a minimum inhibitory concentration (MIC) against Agrobacterium tumefaciens, Erwinia carotovora, Corynebacterium fascians, and Pseudomonas solanacearum. The MIC was dependent on the bioassay test and the bacterial reduction rate increased with the decreasing of the molecular weight (MW). The antifungal activity against Alternaria alternata, Fusarium graminearum, F. oxysporum, F. solani, Phytophthora infestans, and Rhizoctonia solani was evaluated by mycelia radial growth technique. The effective concentration producing 50% mycelia growth inhibition (EC50) of the chitosans ranged from 480 to 3037 mg/L depending on the fungus tested and the MW of the chitosan products. F. graminearum, F. oxysporum, and R. solani were relatively less susceptible, while A. alternata, F. solani, and P. infestans were relatively more sensitive to the chitosan compounds.