Discovery of Sesterdiaporate, an Antifungal Sesterterpene Lactone, against Penicillium italicum, Possibly via Inhibition of Glycosylphosphatidylinositol Biosynthesis from Diaporthe sp. HT-79

The present study reported the discovery of sesterdiaporate (SES), a structurally unique antifungal sesterterpene lactone from Diaporthe sp. HT-79. SES exhibited a pronounced inhibitory effect on spore germination and mycelial growth of Penicillium italicum, with median effective concentrations (EC50) of 0.37 and 0.079 μg/mL, respectively. This inhibitory effect was significantly more pronounced than that observed with prochloraz (0.74 and 6.83 μg/mL, respectively). Treatment with SES resulted in the swelling of both spores and mycelia of P. italicum as well as an increase in cell membrane permeability. Further investigation suggested that SES may disrupt glycosylphosphatidylinositol biosynthesis, ultimately leading to cell death. In vivo tests on navel orange fruit showed that SES was effective in reducing the diameter of lesions caused by P. italicum, with a lesion inhibition percentage of 49.4% at a concentration of 3.7 μg/mL, which was significantly superior to that of prochloraz (14.2% at the same concentration).