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Australian Verticillium dahliae goes against the group – VCG 2A causes severe disease in Australian cotton

Pearl Dadd-Daigle: The University of Technology Sydney

<div>Cotton in Australia is a billion-dollar industry. The industry relies on improved cotton varieties, soil and water management, and weed, insect and disease management for sustainability and growth. One of the many factors that can impact yields is the fungal pathogen <em>Verticillium dahliae</em>, responsible for Verticillium wilt. The soil-bourne ascomycete,<em> V. dahliae</em>, has been classified into two pathotypes, defoliating (D) and non-defoliating (ND), and into Vegetative Compatability Groups (VCGs). Globally the D VCG1A has been reported to cause the most significant damage, but in Australia the ND VCG2A has been seen to cause more damage in the field than the D VCG1A. Four cotton varieties were inoculated with several Australian <em>V. dahliae </em>isolates encompassing VCG1A and VCG2A by root dipping with a concentration of ~1x10<sup>6</sup> conidia. Plants were monitored over a period of 7 weeks and disease severity scored twice weekly. At the end of the monitoring period both the VCG1A isolates and one VCG2A isolate had killed their host while the remaining VCG2A isolates caused only minor disease. This agrees with the field reports that some Australian VCG2A isolates have the ability to cause severe crop damage, a result that has been previously unreported. The identification of highly virulent ND VCG2A strains allows the use of molecular and genomic tools to further understand the nature of virulence in <em>V. dahliae,</em> targeting features not present in other isolates of the same VCG.</div>