Control of Rhizoctonia solani and Sclerotium rolfsii damping-off of tomato plants: preliminary results

Rhizoctonia solani and Sclerotium rolfsii are fungal pathogens responsible for severe crown and stem rot of several horticultural crops in greenhouse and open field. With a two-year survey in tomato (Lycopersicon esculentum) crops of Central and Southern Italy, a high and unusual incidence of the two pathogens was observed. Because of technical, economical and environmental problems, chemical control against this pathogens is difficult. Thus the activity of some antagonistic bacteria (T1A-2B and T4B-2A) isolated from suppressive soils against these pathogens, was tested in experiments carried out on tomato plants grown under controlled and field conditions. The potential antagonists were compared with two commercial biofungicides (Bacillus subtilis, BSF4 and Trichoderma viridae, TV1) and four synthetic fungicides (Tolclofos-metile, Azoxystrobin, Fosetil-Al and Propamocarb+Fosetil-Al). The antagonists as well as other control treatments were applied in the soil near the plant crown and main root and 24 h later plants were artificially inoculated with the pathogens. In both controlled and field conditions the antagonists significantly reduced the incidence and severity of S. rolfsii and R. solani symptoms. The antagonistic bacteria were as effective as Trichoderma viridae TV1, better than Bacillus subtilis BSF4 and comparable with synthetic fungicides, except for Tolclofosmetile which was more effective. Results are discussed also in relation to the optimization of the new potential antagonists for application aimed at an eco-compatible control of crown and root rot of horticultural crops.