INDUCED RESISTANCE IN TOMATO PLANTS TO CLAVIBACTER MICHIGANENSIS subsp. MICHIGANENSIS BY LENTINULA EDODES AND AGARICUS SUBRUFESCENS (syn. AGARICUS BRASILIENSIS)

Abstract

Clavibacter michiganensis subsp. michiganensis can cause severe losses to tomato crops and new types of alternative control must be identified. Induced resistance is a potential method. Among resistance inducers, the mushrooms Lentinula edodes (Le) and Agaricus subrufescens (Abl) exhibit the potential to be used in plant disease control. The objectives of this study were: (i) evaluate the potential of these mushrooms and of acibenzolar-S-methyl (aSm) to control bacterial canker; (ii) study the mode of action of these materials by measuring defense-relate enzyme activity; (iii) partially purify biologically active molecules. The aqueous extracts from mushroom isolates, as well as aSm, did not inhibit bacterial growth in vitro. However, 10% (v/v) solutions of extracts from the isolates Le-96/17 and Abl- 26, as well as aSm, reduced wilt in tomato plants under greenhouse conditions. Plants treated with aSm, Abl-26 and Le-96/17 showed an increase in peroxidase and chitinase. Pphenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activities increased with all treatments. Because isolate Le-96/17 induced the greatest wilt reduction, its aqueous extract was precipitated with ammonium sulfate. The fraction at 40-80% saturation was submitted to anion-exchange chromatography (AEC). The AEC fractions 3 and 4, the inducer aSm and the aqueous extract of Le-96/17 reduced the bacterial disease. The fractions 3 and 4, the 40-80% precipitate and the aqueous extract from Le-96/17 contained more than one protein band. In conclusion, the isolate Le-96/17 induced resistance to C. michiganensis in tomato and partial purification of the inducer molecules was obtained.