Proceedings of the 7 th International Conference on Mushroom Biology and Mushroom Products (ICMBMP7) 2011 QTL FOR RESISTANCE TO TRICHODERMA LYTIC ENZYMES AND METABOLITES IN AGARICUS BISPORUS. MARIE FOULONGNE-ORIOL, NATHALIE MINVIELLE, JEAN-MICHEL SAVOIE. INRA, UR1264 Mycologie et Sécurité des Aliments, F-33883 Villenave d’Ornon, France mfoulong@bordeaux.inra.fr ABSTRACT Trichoderma aggressivum leads to severe crop losses in Agaricus bisporus cultures. The development of strain resistant to this competitor is an alternative to the use of chemicals. One of the interacting components of the putative system of resistance is the lack of susceptibility to the growth limiting compounds produced by Trichoderma sp. Wide variation for this trait has been previously demonstrated, with few strains able to resist to Trichoderma lytic enzymes and metabolites. For exploiting such a resistance in breeding programs, the knowledge of its genetic basis is a prerequisite. Therefore, QTL analysis was used to determine the number, effects and location of genomic regions associated with tolerance to Trichoderma lytic enzymes and metabolites in a hybrid progeny of A. bisporus. An in vitro experiment using sequential cultures on media supplemented or not with a commercial product Lysing Enzyme® was used. The mycelium growth rate in control condition, the level of tolerance and the capacity of adaptation were the traits used for QTL detection. In total for all the traits, seven QTLs were detected distributed on four genomic regions. Two clusters of QTLs related to several traits and two other trait-specific QTLs were identified. A genomic region on LGIV was detected for each trait, with the highest LOD score value and genetic effects. Our results showed that tolerance to Trichoderma lytic enzymes and metabolites was tightly related to mycelium growth ability. Consequences for mushroom breeding program are discussed. Keywords: competitor, green mould disease, adaptation, fitness, breeding INTRODUCTION The fungal competitor Trichoderma aggressivum is the cause of the green mould disease in the cultivated button mushroom Agaricus bisporus. It develops a dense hyphal network in mushroom compost or casing materials, followed by sporulation and an almost complete lack of mushroom production. The T. aggressivum species compete for space and nutrients and are adapted for growth in Agaricus mushroom compost by resisting the inhibiting effects of bacteria in this cultivation substrate [1]. The North American Trichoderma aggressivum f. aggressivum, produces antifungal compounds in mushroom compost that inhibit mycelial growth of the commercial mushroom A. bisporus which results in drastic crop losses [2]. This threat affects an ever larger part of producing areas all over the world and becomes a major disorder in commercial mushroom production [3]. Prophylactic management and disinfectant treatments may limit the epidemic but the severe level of chemical residue in food product together with the increasing risk of fungicide resistance led us to consider the cultivation of resistant A. bisporus varieties as a promising alternative. Little is known about the resistance to T. aggressivum and its mechanism in A. bisporus. Although brown line formation and laccases production were described when Lentinula edodes Section Posters 17