Alternaria and Stemphylium Species Found on Safflower Plants and Seed in Western Australia

New lines of safflower, genetically modified to contain oleic acid above 90% in their oil, have been developed in Australia. The 2022 safflower-growing season in Western Australia was affected by many outbreaks of disease in the crop. Pathogens were isolated from disease-affected tissues from 15 different sites and identified using Sanger sequencing regions of the glyceraldehyde 3-phosphate dehydrogenase (Gapdh) and translation elongation factor 1-α (Tef1) genes. The predominant pathogens identified came from the genera Alternaria and Stemphylium but did not include the known safflower pathogen Alternaria carthami (section Porri). Koch’s postulates tests showed conclusively that Alternaria sect. Alternaria and Stemphylium eturmiunum were causal agents of disease, but tests on other fungal field isolates were inconclusive. The two causal agents confirmed through Koch’s postulates were also the only ones found in grain samples that were tested for fungal contamination and could thus represent a possible source of infection.