Effect of commercial microbial consortia for Organic agriculture on the microbial population of tomato roots and rhizosphere
A commercial microbial consortium (Bacillus spp., Pseudomonas spp., Streptomyces spp., Trichoderma spp., Glomus spp.) was evaluated in Sicily in a cold greenhouse, certified for the organic methods and techniques adopted, and applied by fertigation to five tomato cultivars (one commercial and four Sicilian landraces). The greenhouse was naturally infested with the tomato leaf miner Phthorimaea absoluta, which affected plant growth and yield. Despite the considerable infestation, plants treated by the above-cited microbial consortium showed better growth and higher yield than the control plants. Furthermore, we observed root galls due to nematodes (Meloidogyne spp.) as the soil was not disinfected. Significant differences among the cultivars, and between the plants treated and untreated were observed. To investigate the effect of the microbial consortium on the tomato root microbiome, microbial DNA was extracted from tomato roots and it was analysed by amplicon sequencing to characterize the root-associated bacterial and fungal, plus nematode, communities. Alpha diversity indices were largely unaffected for bacteria. In contrast, plant genotype and the soil treatment by the microbial consortium affected the alpha diversity indices for fungi and nematodes. Analysis of beta diversity indices revealed significant differences between microbiota community composition of the plants grown in treated and untreated soil for both datasets analysed. Furthermore, we found several OTUs (bacteria, fungi and nematodes) associated with the soil treatment by the microbial consortium utilized. Finally, our results demonstrated that the plants treated by the microbial consortium utilized increased the resistance of the tomato plant against biotic stress (P. absoluta and Meloidogyne spp.). Furthermore, the treatment significantly affected the microbial community of the tomato roots depending on the cultivars used.    Furthermore, data from another experiment are included. The effect of different experimental microbial consortia was evaluated for plant growth promoting when applied for seed dressing and soil drenching on tomato seedlings. The seeds were sowed in a commercial greenhouse and the plant growth was monitored for 43 days. Based on the results of the plant growth promotion, two microbial consortia were selected and compared with the untreated control to investigate the effect of the microbial consortia on the tomato rhizosphere.