The Effect of Biopreparations and Biostimulants on the Chemical Composition and Microorganisms Associated with Verticillium Wilt of Horseradish Roots (Armoracia rusticana Gaertn.)

The basic foundation of plant production consists in plant protection treatments, which largely shape the quality of plant raw material intended for the food industry. Due to its long growing season, horseradish requires more treatments than average. Intensive protection based on synthetic pesticides favours the accumulation of their residues in plants and generates serious environmental problems. We have examined the effect of chemical protection and its reduced variant as well as three variants of biological protection, differentiated in terms of preparations used for seedlings treatment (Pythium oligandrum, Bacillus subtilis, and Ecklonia maxima), on the content of dry matter, protein, fat, carbohydrates, and the disease severity index (DSI) of Verticillium wilt of horseradish roots. The quantitative and qualitative changes in the microorganism communities associated with this disease were determined. Thirty-four species of fungi and Globisporangium irregulare have been shown to contribute to the pathogenesis of Verticillium wilt. The following were found with the highest frequency: Verticillium dahliae (14.37%), G. irregulare (6.87%), Ilyonectria destructans (6.73%), Fusarium acuminatum (6.53%), Rhisoctonia solani (6.75%), Epicoccum nigrum (5.56%), and Alternaria brassicae (5.36%).We found that water deficit promotes the increase of DSI and reduces the number and richness of fungal species isolated from diseased roots. The variant of biological protection with treatment of seedlings of E. maxima extract and with reduced chemical protectionin dry seasons give the best protective effects. Under conditions of optimal water supply, biological protection (P. oligandrum) is more effective than chemical protection. Biological protection increases biodiversity in the population of microorganisms that contribute to blackening of the conductive bundles of horseradish roots. There is a significant negative correlation between the number of isolated microorganisms and the DSI value. Increasing the number of the CFUs is accompanied by a reduction in the symptoms of Verticillium wilt of horseradish roots. Biological protection in years with sufficient water supply results in a significant increase in the content of dry matter, protein, and carbohydrates in horseradish roots. Under the influence of protective treatments, the ash content in the roots and its alkalinity decrease.