Infection studies of Cicer arietinum (L) with GUS-(E-coli beta-glucuronidase) transformed Ascochyta rabiei strains

Ascochyta rabiei (Pass) Labr. was transformed with the GUS-(beta-glucuronidase) reporter gene of E. coli. Integration of vector-DNA into the A. rabiei genome was documented by Southern analysis. To verify that the transformation process had not adversely affected biochemical traits potentially important for fungal pathogenicity, i.e. hydrolytic exoenzymes, the extent of solanapyrone-toxin production and phytoalexin degradation were measured. Significant differences between the transformants and the wildtype were not observed. Transformants also showed the same degree of virulence as the wildtype A. rabiei strain. Histological studies with the GUS-transformed genotypes were per formed and the time course of infection was monitored by light microscopy. A. rabiei penetrates its host directly through the cuticle and penetration through hydathodes has also been found. After penetration, A. rabiei spreads mainly in the apoplast. When growing through leaflets towards petioles, the fungus could mainly be found in the apoplast and in the cells of phloem, but rarely in xylem. The infection process leads to a total collapse of plant tissue with extensive formation of pycnidia near the vascular tissue.