Trichoderma Species Differ in Their Volatile Profiles and in Antagonism Toward Ectomycorrhiza Laccaria bicolor

Abstract

Fungi of the genus <i>Trichoderma</i> are economically important due to their plant growth- and performance-promoting effects, such as improved nutrient supply, mycoparasitism of plant-pathogens and priming of plant defense. Due to their mycotrophic lifestyle, however, they might also be antagonistic to other plant-beneficial fungi, such as mycorrhiza-forming species. <i>Trichoderma</i> spp. release a high diversity of volatile organic compounds (VOCs), which likely play a decisive role in the inter-species communication. It has been shown that <i>Trichoderma</i> VOCs can inhibit growth of some plant pathogens, but their inhibition potentials during early interactions with mutualistic fungi remain unknown. <i>Laccaria bicolor</i> is a common ectomycorrhizal fungus which in symbiotic relationship is well known to facilitate plant performance. Here, we investigated the VOC profiles of three strains of <i>Trichoderma</i> species, <i>Trichoderma harzianum, Trichoderma Hamatum</i>, and <i>Trichoderma velutinum</i>, as well as <i>L. bicolor</i> by stir bar sorptive extraction and gas chromatography - mass spectrometry (SBSE-GC-MS). We further examined the fungal performance and the VOC emission profiles during confrontation of the <i>Trichoderma</i> species with <i>L. bicolor</i> in different co-cultivation scenarios. The VOC profiles of the three <i>Trichoderma</i> species were highly species-dependent. <i>T. harzianum</i> was the strongest VOC emitter with the most diverse compound pattern, followed by <i>T. hamatum</i> and <i>T. velutinum</i>. Co-cultivation of <i>Trichoderma</i> spp. and <i>L. bicolor</i> altered the VOC emission patterns dramatically in some scenarios. The co-cultivations also revealed contact degree-dependent inhibition of one of the fungal partners. <i>Trichoderma</i> growth was at least partially inhibited when sharing the same headspace with <i>L. bicolor</i>. In direct contact between both mycelia, however, <i>L. bicolor</i> growth was impaired, indicating that <i>Trichoderma</i> and <i>L. bicolor</i> apply different effectors when defending their territory. Multivariate analysis demonstrated that all examined individual fungal species in axenic cultures, as well as their co-cultivations were characterized by a distinct VOC emission pattern. The results underline the importance of VOCs in fungal interactions and reveal unexpected adjustability of the VOC emissions according to the specific biotic environments.