A Morphological and Molecular Perspective of Trichoderma viride : Is It One or Two Species?

Abstract

Trichoderma (Ascomycetes,Hypocreales) strains that have warted conidia are traditionally identified as T. viride, the type species ofTrichoderma. However, two morphologically distinct types of conidial warts (I and II) have been found. Because each type corresponds to a unique mitochondrial DNA pattern, it has been questioned whether T. viride comprises more than one species. Combined molecular data (sequences of the internal transcribed spacer 1 [ITS-1] and ITS-2 regions and of part of the 28S rRNA gene along with results of restriction fragment length polymorphism analysis of the endochitinase gene and PCR fingerprinting), morphology, physiology, and colony characteristics distinguish type I and type II as different species. Type I corresponds to “true” T. viride, the anamorph of Hypocrea rufa. Type II represents a new species, T. asperellum, which is, in terms of molecular characteristics, close to the neotype of T. hamatum.

Delineation of species within the complex by UP-PCR cross-blot hybridization

“…The distribution of T. viride strains into four groups also indicates that more species could perhaps be defined as is suggested from morphological observations and preliminary EF-1a sequence data by Dodd et al [10]. The heterogeneity of ''true'' T. viride revealed here and by Lieckfeldt et al [7] suggests that a further revision of this species is needed.…”

“…The weak signals corresponding to DNA hybridization values between 40% and 60% between some strains of the eight hybridization groups can be used as an estimate of how closely related the species are. The recently discovered species T. asperellum seems thus to be well separated as first found by Lieckfeldt et al [7] and Samuels et al [9]. In Table 2 UP-PCR cross-hybridization of Trichoderma strains Species Strain no.…”

“…By UP-PCR cross-hybridization 16 Trichoderma strains were distributed into eight hybridization groups which correspond perfectly with previous characterization of the strains using CA [7]. CA was carried out on a mixed-type data set containing information from morphological, physiological and molecular studies, 55 characters in total.…”

“…The correlation of the eight hybridization groups with the grouping of the strains based on correspondence analysis (CA) of a large number of molecular and morphological characters obtained by Lieckfeldt et al [7] are shown in Table 1.…”

“…Since RifaiÕs [1] revision of Trichoderma, in which he operated with species aggregates, considerable effort has been devoted to define species in this genus [2][3][4]. The combination of molecular data (in particular rDNA sequences) and morphology has proven useful for reevaluation (neotypification) of known and widely accepted species [5][6][7][8], for recognition of new species [9] and for linking of anamorphs with their respectively teleomorphs [6,10]. The rDNA sequences have also been used to phylogenetically evaluate the sections of Trichoderma proposed by Bissett [2,[11][12][13][14].…”