Effects of biofumigation using Brassica juncea and Raphanus sativus in comparison to disinfection using Basamid on apple plant growth and soil microbial communities at three field sites with replant disease

Aims The effects of biofumigation with Brassica juncea ‘Terra Plus’ and Raphanus sativus ‘Defender’ in comparison to Basamid on apple plant growth and on soil microbial communities were studied at three sites affected by replant disease under field conditions. Methods Apple rootstocks were planted on differently treated plots to evaluate the effect of the treatments on plant growth under field and greenhouse conditions. The glucosinolates in biofumigant plant organs and their breakdown products in soils were determined. Denaturing gradient gel electrophoresis fingerprints were performed with 16S rRNA gene and ITS fragments amplified from total community DNA extracted from different soils. Results The highest glucosinolate concentrations were found in inflorescences of both biofumigant plant species with no differences between sites. The most abundant degradation product in soil biofumigated with B. juncea was 2-propenyl isothiocyanate, while in soil treated with R. sativus only 4-(methylthio)-3-butenyl isothiocyanate was detected. Effects of biofumigation were recorded to be stronger on fungi than on bacteria. Growth of apple rootstocks was positively affected by the treatments in a site-dependent manner. Conclusions The effects of biofumigation evaluated by the apple plant growth were site-dependent and might result from suppression of soil-borne pests and pathogens, changes in soil microbial community compositions, and additional nutrients from the incorporated biomass.