Impact of type and dose of biochar and hydrochar on growth response of phytopathogenic and antagonistic soil-resident fungi

Biochar (BC) and hydrochar (HC) are solid by-products obtained through, respectively, pyrolysis and hydrothermal carbonization of biomass. Both materials are used as organic amendments allowing carbon sequestration in soil. Two BCs, from spruce pellets (BCSP) and grapevine pruning residues (BCGV), and two HCs, from urban pruning residues (HCUP) and the organic fraction of solid urban waste (HCSU), were tested at concentrations of 0.2 and 1% (w/v) on soil-resident fungi. The higher dose of BC samples significantly reduced mycelial growth of the phytopathogens Rhizoctonia solani and Botrytis cinerea (up to 53% for BCGV on B. cinerea after 24 h from inoculation, compared to control), whereas, in general, the lower dose of both BCs inhibited R. solani for the whole experiment and B. cinerea only initially. HC samples evidenced a general lower toxicity on the two pathogens than BCs. In fact, only HCUP at both concentrations reduced hyphal elongation of the sole B. cinerea for the entire experimental time (up to of 38% for both doses at 24 h from inoculation). All BC and HC treatments at the lower concentration did not influence or greatly stimulated the antagonists Trichoderma harzianum and T. virens. Differently, the higher dose of these materials caused some suppression at the initial stage or at each sampling by BCSP on T. harzianum and HCUP on T. virens. The whole results obtained indicate a plant protective activity of these materials with consequent less need for fungicidal treatments.