Abstract: Substance F-0368 of the formula: ##STR1## or salts thereof is prepared by culturing Kitasatosporia sp. F-0368 in a culture medium thereby producing substance F-0368, and then isolating and collecting substance F-0368 from the culture medium.

Abstract: Disclosed in the present invention are: a substance F-0368 or salts thereof having the following structural formula ##STR1## a method for production of the substance F-0368 or salts thereof, wherein an F-0368-substance-producing-microorganism belonging to a genus Kitasatosporia is cultured, and the substance F-0368 is isolated and collected from the cultured substance; a method for production of the substance F-0368 or salts thereof, wherein 3-methyl-4-lower alkoxy carbonyl-2(5H)-furanone represented by the following general formula is subjected to hydrolytic reaction ##STR2## (where: R represents a straight or branched lower alkyl group having 1 to 6 carbon atoms); a composition which consists essentially of the substance F-0368 or salt thereof, a diluent permissible in the agricultural chemicals, and a carrier or an excipient; a preventive agent for plant diseases such as rice blast disease and bacterial leaf blight disease, which consists essentially of an effective amount of the substance F-0368 or salts