GENETIC DIVERSITY AND VEGETATIVE COMPATIBILITY AMONG TRICHODERMA-HARZIANUM ISOLATES

Trichoderma harzianum is the collective name of a set of asexual funga l strains which exhibit heterogeneity in genome structure, DNA sequenc e and behavior. Contour-clamped homogeneous field (CHEF) electrophores is of the chromosomes of ten isolates of T. harzianum revealed six cle arly distinct electrophoretic karyotypes. Of the ten isolates analyzed , four (GH12, G109, Y and YF) could be classified in a single group wi th identical karyotypes, while the strains T35 and 315 formed a second group. The genome size characteristic of the different isolates fell into a broad range varying from 29.6 to 56.1 Mb. Gene assignments to t he resolved chromosomes showed that all genes analyzed were localized on equivalent chromosomes in the isolates belonging to the same group. Analysis of randomly amplified polymorphic DNAs from the ten isolates confirmed the classification into groups and allowed us to distinguis h between isolates T35 and 315, as well as between isolates GH12, G109 , Y and YF. Direct confrontation assays using isolates of the same gro up showed compatible interactions, whereas the same experiment carried out with isolates of different groups showed an incompatible interact ion characterized by an area of cell damage. Microscopic observation o f the compatible interactions showed hyphal fusions between the isolat es, similar to those described for vegetative compatible groups in oth er fungi. The molecular karyotypes correlated well with the compatibil ity of the isolates. In addition, we have evaluated both electrophoret ic karyotype and randomly amplified polymorphic DNAs analysis as crite ria for grouping isolates within the genus according to their capacity for biocontrol of plant pathogens.