Verticillium wilt is a soil-borne disease caused by distinct vegetative compatibility groups (VCG) of the fungus Verticillium dahliae. Defoliating (VCG 1A) and non-defoliating (VCG 2A) pathotypes of V. dahliae have contributed to yield losses of cotton production in Australia. To study the virulence and the infection process of V. dahliae on cotton, two isolates, one representing each VCG, have been transformed with fluorescent protein genes. The transformants maintained their ability to infect the host, and both strains were observed to move through the plant vasculature to induce wilt symptoms. Furthermore, virulence testing suggests that the cotton V. dahliae strains can endophytically colonise common weed plant species found in the Australian landscape, and that is contrasted by their ability to infect and colonise native tobacco plants. The fluorescently labelled strains of V. dahliae not only allowed us to gain a thorough understanding of the infection process but also provided a method to rapidly identify recovered isolates from host colonisation studies.

Verticillium wilt is a soil borne disease caused by distinct vegetative compatibility groups (VCG) of the fungus Verticillium dahliae. Two V. dahliae isolates were recovered from symptomatic cot-ton plants in Australian cotton fields and were assigned to two distinct vegetative compatibility groups (VCGs). One corresponding to the defoliating (VCG 1A) and the other non-defoliating (VCG 2A) pathotypes of Verticillium, have been transformed with Red and Green Fluorescent protein genes, respectively. The transformants maintained their ability to infect cotton and both strains were observed to colonise the xylem vessels of cotton plants. Moreover, we observed that the cotton V. dahliae strains could also infect some sampled non-Gossypium species found in the Australian landscape. The fluorescently labelled strains of V. dahliae will allow us to gain a thorough understanding of the infection processes of this important pathogen.