Toxin Production by Alternaria alternata in Black Spot Disease of Chrysanthemum morifolium ‘Fubai’: Accumulation of Altenuene and Tenuazonic Acid in Flowers

Alternaria species produce diverse secondary metabolites that act as critical virulence factors during plant pathogenesis. In cultivation areas of Chrysanthemum morifolium ‘Fubai’—a key cultivar for herbal tea—black spot disease caused by A. alternata manifests as necrotic leaf lesions progressing to wilting. Despite this disease’s economic impact, information on its associated toxins is limited, and the types of toxins produced by the black spot pathogen of Chrysanthemum morifolium ‘Fubai’ in particular remain unclear. Furthermore, whether toxins are present in the flowers when the leaves show symptoms is uncertain, but their inflorescence is not visibly infected. Using two previously characterized A. alternata strains (F16/F20) isolated from ‘Fubai’ in earlier studies, we demonstrated the concomitant production of altenuene (ALT) and tenuazonic acid (TeA) in both strains, with strain-specific yield variations (F20 TeA: 342.16 µg/mL vs. F16: 21.84 µg/mL; ALT: 0.28 µg/mL vs. 0.90 µg/mL). Time-course monitoring revealed coordinated accumulation of both toxins in inoculated petals, reaching 18.07 μg/g ALT and 2.59 µg/g TeA by day 9. Notably, these two toxins were detected only in flower samples from black spot-infected plants, and their concentrations correlated closely with disease severity in the leaves. Moreover, although the inflorescences did not display symptoms, both fresh and dried flowers retained detectable toxin levels. We established a technical system for the extraction and quantitative detection of the toxins ALT and TeA produced by the black spot pathogen in tea chrysanthemum. This work provides the first confirmation of ALT/TeA co-contamination in Chrysanthemum morifolium ‘Fubai’, revealing substantial dietary exposure risks through tea consumption. Our findings suggest that, from a food safety risk reduction perspective, integrated management strategies should be developed to minimize toxin contamination in tea chrysanthemum, including improved disease prevention measures and potential regulatory considerations.