Secondary Metabolites with Herbicidal and Antifungal Activities from Marine-Derived Fungus Alternaria iridiaustralis

Weed and soil-borne pathogens could synergistically affect vegetable growth and result in serious losses. Investigation of agricultural bioactive metabolites from marine-derived fungus Alternaria iridiaustralis yielded polyketides (1–4), benzopyrones (5–7), meroterpenoid derivatives (8), and alkaloid (9). The structures and absolute configurations of new 1, 3, 5–6, and 8 were elucidated by extensive spectroscopic analyses, as well as comparisons between measured and calculated ECD and (13)C NMR data. Compounds 1–4, 6, and 9 showed herbicidal potentials against the radicle growth of Echinochloa crusgalli seedlings. Especially 9 exhibited inhibition rates over 90% at concentrations of 20 and 40 μg/mL, even better than the commonly used chemical herbicide acetochlor. Furthermore, 9 also performed a wide herbicidal spectrum against the malignant weeds Digitaria sanguinalis, Portulaca oleracea, and Descurainia sophia. Compounds 5–8 showed antifungal activities against carbendazim-resistant strains of Botrytis cinerea, with minimum inhibitory concentration (MIC) values ranging from 32 to 128 μg/mL, which were better than those of carbendazim (MIC = 256 μg/mL). Especially 6 exhibited integrated effects against both soil-borne pathogens and weed. Overall, marine-derived fungus A. iridiaustralis, which produces herbicidal and antifungal metabolites 1–9, showed the potential for use as a microbial pesticide to control both weed and soil-borne pathogens.