The Toxin Cercosporin is a Virulence Factor for Infection of Coffee by Cercospora coffeicola

Brown eye spot, caused by , causes significant losses in both quality and quantity of coffee production. As many spp. produce the photoactivated toxin cercosporin, this study aimed to determine the role of cercosporin in pathogenesis by creating disruption mutants unable to produce the toxin. Six isolates from Brazilian fields, representing organic and conventional production systems in the Minas Gerais state, were evaluated for their ability to produce cercosporin . Toxin production varied among isolates, ranging from 3.5 – 25.3 µM/ 5 mm mycelial plug; production was undetectable in one isolate. The homolog of the polyketide synthase gene () involved in cercosporin production was amplified using a degenerate primer strategy. The 7044 nt gene sequence was 90.3% identical to the gene in and encoded a putative protein of 2196 amino acids with 98.2% similarity and 97.5% identity to its counterpart in . Transformation of two isolates of with a disruption construct resulted in the recovery of six disruption mutants. All of the disruptants were deficient in cercosporin production. Disruption mutants did not differ significantly from the wild type for either growth or sporulation, but were significantly altered in virulence on coffee. As compared to wild type, time to lesion development was significantly increased and numbers of lesions were significantly decreased in coffee plants inoculated with disruption mutants. These results show that cercosporin toxin is a virulence factor for infection of coffee.