Suppressiveness of white vinegar and steam-exploded liquid waste against the causal agents of Pleurotus eryngii yellowing.

During a survey of mushroom-beds in Apulia and Basilicata (southern Italy), several bacterial strains belonging to the fluorescent Pseudomonads group have been isolated from the basidiomata of Pleurotus eryngii on account of symptoms of yellowing. On the basis of LOPAT tests, 95% of the recovered bacteria were identified as Pseudomonas fluorescens. In particular, 83% of them were recognized as P. ‘reactans’ because they were able to produce a white line against P. tolaasii strain NCPPB-2192. In preliminary in vitro experiments, commercial white vinegar (WV) and steam-exploded liquid waste (SELW) solution derived from Miscanthus sinensis biomass proved to have an effective antibacterial activity against P. ‘reactans’, P. tolaasii and fluorescent pseudomonads isolates used as targets. In particular, WV induced a bacterial inhibition reaching 89% and 65% on tested P. ‘reactans’ and fluorescent pseudomonads strains, respectively. Undiluted M. sinensis SELW reached an inhibition of 20–50% against tested strains. No antibacterial effects were associated with Arundo donax and wheat straw SELWs. The bacterial suppressiveness of WV and M. sinensis SELW was subsequently studied in vivo throughout two “cardoncello” mushroom cropping cycles performed under protected environmental mushroom-bed conditions using the P. eryngii commercial strain “3065” and six Pseudomonas strains (3 belonging to P. ‘reactans’, 2 to P. fluorescens and 1 to P. tolaasii). Cell suspensions of the single Pseudomonas strains were sprayed as inoculum onto covering soil as soon as “cardoncello” primordia appeared. Specifically, WV with 6‰ acidity and M. sinensis SELW, were effective as antibacterial substances. In particular WV led to a 4.5–6.1, 2.2–4.3 and 3.5–4.4-fold increase in sporophore yield when sprayed: a) on the surface of substrates colonized by “cardoncello” mycelium right before casing soil distribution, b) right after casing soil distribution and c) on casing soil and basidioma surface at 3–4-day intervals. M. sinensis SELW increased the sporophore yield 6.1-fold when sprayed right after casing soil distribution.