Biological Control of Sclerotinia sclerotiorum the Causal Agent of Lettuce Rot Disease by Use of Soil Streptomycetes

Abstract

Sclerotinia sclerotiorum (Lib) De Bary, the causal agent of lettuce rot, is asoil borne fungal pathogen which can cause extensive damage to infected plants or crop and occurs world over. It is difficult to control this pathogen by normal cultural and chemical practices. Our studies have shown that the pathogen can be managed by by use of bacteria belonging to the actinomycetes group. Preliminary screening of 40 soil isolates of actinomycetes from Kerman province of Iran was carried out for testing their ability to inhibit Sclerotinia sclerotiorum by using in vitro agar disk and dual culture evaluations. Among the tested isolates, Actinomycetes isolates B, F and S showed reasonable inhibitory capabilities in dual culture. These isolates were positive forchitinase, Amylase, Protease and Lipase activities but none of them produced HCN. Minimal inhibitory concentration of the active crude extracts varied from1.25 to 0.312 mg/ml and the thermal inactivation point was determined between 90-120°C. All three isolates had fungicidal activity and only isolate F retained its antifungal activity after exposure to chloroform. Significantly, all three isolates reduced the severity of the disease in greenhouse evaluations.