Inhibitory effect of antagonistic bio-agents and chitosan on the growth of tomato root rot pathogens In vitro

Abstract Fungal and bacterial bio-agents and the by-product chitosan as fungicides alternatives were evaluated for their inhibitory effect against the growth of tomato root rot pathogenic fungi under laboratory conditions. The tested pathogenic fungi were Fusarium oxysporum radicisycopersici, F. oxysporum lycopersici, F. solani, Rhizoctonia solani, Sclerotium rolfsii, Macrophomina phaseolinae, Pythium sp. and Phytophthora sp., Meanwhile, isolates of the antagonistic microorganisms, i.e. T. harzianum, T. viride, Bacillus subtilis, and P. fluorescens. Mycelial growth of pathogenic fungi was significantly reduced by the inhibitor action produced by all antagonistic agents tested. The antagonistic fungi had a greater effect on the retardation of growth (75.5--100%) compared with the bacterial agents (57.7-83.3%). The inhibitor effect of the two tested chitosan (High and Low molecular weight) was increased as chitosan concentration is increased in growth medium to reach its maximum at the highest concentration (5 g/L). Complete inhibition of tested fungal growth was observed at the concentration of 4 g/L of LMW chitosan, while the highest fungal growth reduction was recorded in PDA-amended with HMW at the same concentration. On the light of the present study, it could be suggested that the use of chitosan as natural safe materialsalone or in combination with bio agents is considered one of low cost and effective applicable methods for controlling such soil-borne plant pathogens causing plant diseases