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

Abstract

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