Combined effects of alternative casing materials and biostimulants on Agaricus bisporus yield and disease incidence Florien A. Gorter1, Marc Hendriks1, Odette Mendes1, Carin Lombaers1, Marjon Krijger1, Ed Hendrix1, William Kay2, Gail Preston2, Jaime Carrasco2,3, Pablo Martinez3, and Jean M. van der Wolf1 1 Wageningen University and Research, Biointeractions and Plant Health, Wageningen, NL, 2 University of Oxford, Department of Plant Sciences, Oxford, UK, 3 Mushroom Technological Research Center of La Rioja (CTICH), La Rioja, Spain Background Casing soil is a complex substrate that is essential for the fructification of Agaricus bisporus mushrooms. Currently, casing soil mainly consists of peat, which is used because of its excellent physical, chemical and biological properties. However, peat excavation is associated with CO2- emissions and biodiversity loss. As such, the mushroom industry is looking for alternative casing materials that can be used to—partially or wholly—replace peat. We identified materials that can be used to partially replace peat without major negative effects on mushroom yield or disease incidence. Performance of alternative casing materials might be improved by the addition of beneficial microbes. Bacterial strains from peat have been isolated that potentially enhance fructification of the mushroom crop. Strains have also been identified that selectively inhibit fungal pathogens such as Lecanicillium fungicola (dry bubble disease) in vitro. Addition of selected biostimulant strains might thus help to overcome the drawbacks associated with the use of alternative casing materials and reduce the use of pesticides. Results Objective Experimental set-up Conclusions • Biostimulants had no effect on yield or dry bubble disease incidence. • Biostimulant A was able to persist in casing soil during two flushes. • Biostimulant B populations decreased rapidly in casing soil. Button mushrooms were grown on three different casing soils (peat, alternative I and alternative II) under standard conditions in an experimental mushroom facility for two consecutive flushes. Mushroom yield was determined in the absence vs. presence of biostimulants A, B or a mix of A, B, and C. Disease incidence following inoculation with Lecanicillium fungicola was determined in the absence vs. presence of biostimulants A, B or a mix of A, B, and C. Population dynamics of biostimulants A and B in the absence of Lecanicillium was determined using targeted TaqMan qPCR assays. Acknowledgements The work presented here was performed as part of the H2020 BIOSCHAMP project (Grant Agreement 101000651), which aims to take an integrated approach to tackle mushroom cultivation challenges. BIOSCHAMP partners are: the Spanish Associations of Mushroom Growers (ASOCHAMP), Research Center of Mushrooms (CTICH), Inagro vzw, Wageningen Research, IRNASA-CSIC, University of Oxford, Kekkilä- BVB, NEWFOSS, FERTINAGRO, EUROCHAMP, UGLK, EKOFUNGI and Innovarum. Wageningen University & Research P.O. Box 123, 6700 AB Wageningen Contact: florien.gorter@wur.nl T + 31 (0)317 48 44 45 Figure 4. Population dynamics of biostimulants in the absence of Lecanicillium fungicola. Absolute abundance determined using TaqMan assays. Ct = cycle threshold, i.e. number of PCR cycles required for the fluorescent signal to cross the threshold. Detection threshold: 35. Biostimulants were added at the beginning of the 1st and 2nd flush (orange arrows) and sampling was performed at multiple time points during the flushes. A) Biostimulant A. B) Biostimulant B. 0 5 10 15 20 25 30 35 40 45 T0 T1 T2 T3 T4 T5 T6 T7 Ct Sampling timepoints A 0 5 10 15 20 25 30 35 40 45 T0 T1 T2 T3 T4 T5 T6 T7 Ct Sampling timepoints B Figure 1. A) Agaricus bisporus growing in the experimental mushroom facility. B) Lecanicillium fungicola (dry bubble disease) causes deformations and brown spots on the mushroom (pictures from Berendsen et al., 2010, A = healthy, B-D = diseased). A B Figure 2. Effect of biostimulants