Chitinase and peroxidase isoenzymes in sugar beet leaves treated with Trichoderma against Cercospora beticola

The effect of the antagonistic fungus Trichoderma on sugar beet defence response has been studied. Sugar beet plants at 6 leaves stage were treated with 10-day old liquid culture (diluted 5 times in PDB, 16.6x10 super(6) cfu/ml) of the Trichoderma isolate BA12/86 (ISCI collection). The treatment was applied on one leaf of each plant, while C. beticola (1x10 super(5) conidia/ml) was inoculated on untreated leaves of the same plants, two days after. Untreated - non inoculated plants and untreated - inoculated plants served as controls. The experiment was carried out with the cultivars Aaron (susceptible to C. beticola) and Faro (partially resistant), on 9 plants per treatment, under greenhouse conditions and was repeated twice. Three, 5 and 7 days after the inoculation, untreated leaves were excised and proteins were extracted, separated by SDS-PAGE and IEF and their chitinase and peroxidase enzymatic activities were determined. Trichoderma treatment induced an increase of the expression of chitinase isoforms with a MW of 50 Kda and a high expression of peroxidase activity in plants treated and inoculated with the pathogen, compared to inoculated untreated plants. Peroxidase isoenzymes showed a 4-5 PI range. The antagonist induced a higher enzymatic activity in Faro than in Aaron cultivar. Furthermore, the induction of the enzymatic activities persisted at a steady level during all the time of the treatment.