Effect of reuse of agro-industrial wastewaters on the agricultural soil microbial community, product safety and product yield in tomato cropping

In the frame of PON In.Te.R.R.A. project, we evaluated the effect of two different irrigation water (conventional well water, CW vs. agro-industrial wastewater, IW) on the microbial community of irrigated soil during tomato (Solanum lycopersicum) production. Triplicate soil samples were collected at 6 time points, during 4 months interval that comprises pre-culture phase and the day before harvest. Bacterial populations were analyzed by Automated Ribosomal Intergenic Spacer Analysis (ARISA). The principal foodborne pathogenic bacteria (Salmonella spp. Campylobacter jejuni, Listeria Monocytogenes and STEC) where monitored in water, soil and final product. Canonical Correspondence Analysis (CCA) showed that ARISA clustered the samples according to temporal variation and to different water used for irrigation. Moreover, molecular fingerprinting analysis showed good correlation with different geochemical parameters, with positive correlation for nitrogen, phosphorous and conductivity and negative correlation with pH, TOC and SOM. Interestingly crop yield was found to be lower (-8,6 ±3,2 %) for the fields irrigated with IW. Both water types, so as tomato plants and berry were found to be pathogen-free, whereas L. monocytogenes and Salmonella spp. were detected in soil, independently from the water source used for irrigation. Basing upon described results, microbial community dynamic is strongly influenced by different water used for irrigation, and even if microbiological quality of agro-industrial wastewater was satisfactory, the chemical composition of IW (particularly high salinity) may have negatively influenced the product final yield.