Population gentics and speciation in Trichoderma

Species of the deuteromycetous genus Trichoderma are cosmopolitan and typically soil-borne or wood decaying fungi. Some of them are economically important because of their production of industrial enzymes (cellulases and hemicellulases), antibiotics, and their action as biocontrol agents. Teleomorphs (=the sexual forms) of the genus Trichoderma, where known, occur in the genera Hypocrea, Podostroma and Sarawakus of the Hypocreaceae. Because of the importance of this genus in industry, plant protection and ecology in general, identification of species within the genus is an important issue. The dominant fungal operational species concept is the morphological species concept (MSC), and consequently morphological species recognition (MSR, which uses morphological or phenotypical characters) is still the prefered diagnostic approach. However, definition of species in Trichoderma has been and is still problematic, because of intergradation of morphological and phenotypic characters between recognized species and also between Trichoderma and other hypomycetes such as Gliocladium. Taxa currently recognized may as well be clonal lines or populations. As a solution to this problem, phylogenetic species concepts have been developed for fungi. In view of these available techniques and theoretical frameworks, the present project aims at understanding the population genetics and contribution to speciation in Trichoderma, involving typing an appropriate number of isolates (100 - 150 per investigated group). For population genetics, three methods (SNPs, microsatellite sequnce analysis, and AFLP) will be tested for their resolution. The best suited method will then, together with sequence analysis of several nuclear genes (ITS1 and 2, ech42, tub1, cal1, tef1, cbh1), and evaluation by phylogenetic and evolutionary statistic methods, be used to obtain answers for the following two questions: (i) what is the prefered mode of reproduction of selected taxa (complexes) in different sections (i.e. asexual or sexual?); and (ii) can a coalescent approach determine whether the recognized species in Trichoderma are populations, clonal lines and species?

The fungal genus Trichoderma is used for various purposes in industrial enzyme production, secondary metabolite formation, and biocontrol of plant pathogens. However this use has always been strongly impaired by the difficulties associated with correctly identifying its species. In the course of this project, we have used molecular and bioinformatics tools to investigate the mechanisms which lead to speciation in Trichoderma, and how these species could be best identified. In our hands, the Genealogical Concordance Phylogenetic Species Concept worked best to this end. A comparative analysis of several nuclear encoded gene sequences showed that different species of Trichoderma have different modes of evolution: the biocontrol fungus T. harzianum consists of a single, world- wide sexually propagating population of species, from which only some 2-4 Mio years ago a new haplotype segregated and established itself as separate cryptic species morphologically indistinguishable from the former; in contrast, the two new oyster-mushroom epidemic species T. fulvum and T. pleurotuphilum which are genetically very similar to each other as well as to T. harzianum each consist of a largely anamorphic population, from which the latter emerged as a serious mushroom pathogen which is accompanied by a loss of some physiological traits and a change in its key morphological characters. In the T. koningii species aggregate, several lineages provided evidence for allopatric speciation. The data show that there is no uniform mechanism for formation of species with Trichoderma and even phylogenetically closely related species may display strongly different mechanisms.