Two Phytotoxins Isolated from the Pathogenic Fungus of the Invasive Weed Xanthium italicum

Abstract

Alternariol and altenuisol were isolated as the major phytotoxins produced by an Alternaria sp. pathogenic fungus of the invasive weed Xanthium italicum. Altenuisol exhibited stronger phytotoxic effect compared with alternariol. At 10 μg/mL, alternariol and altenuisol promoted root growth of the monocot plant Pennisetum alopecuroides by 11.1 % and 75.2 %, respectively, however, inhibitory activity was triggered by the increase of concentration, with root elongation being suppressed by 35.5 % and 52.0 % with alternariol and altenuisol at 1000 μg/mL, respectively. Alternariol slightly inhibited root length of the dicot plant Medicago sativa at 10-1000 μg/mL, whereas altenuisol stimulated root growth by 51.0 % at 10 μg/mL and inhibited root length by 43.4 % at 200 μg/mL. Alternariol and altenuisol did not exert strong regulatory activity on another dicot plant, Amaranthus retroflexus, when tested concentration was low, however, when the concentration reached 1000 μg/ mL, they reduced root length by 68.1 % and 51.0 %, respectively. Alternariol and altenuisol exerted similar effect on shoot growth of three tested plants but to a lesser extent. It is noteworthy to mention that this is the first report on the phytotoxicity of altenuisol.

Phytotoxic Secondary Metabolites from Fungi

“…Both alternariol (18) and alternuisol (22) were isolated from the cultures of Alternaria sp., the pathogen of the invasive weed Xanthium italicum. They inhibited shoot and root growth of Pennisetum alopecuroides and Medicago sativa by seedling growth assay [43]. Further stud-ies on the mode of action showed that alternariol (18) and alternariol-9-methyl ether (also called AME, 19) from Alternaria alternata inhibited the photosynthetic electron transport chain in isolated spinach chloroplasts [44].…”

“…Agropyrenal (43), a naphthol, was isolated from the liquid cultures of Ascochyta agropyrina var. nana.…”

“…nana. When the leaves of several weed plants (i.e., Mercurialis annua, Chenopodium album and Setaria viridis) were assayed, agropyrenal (43) was proved to be phytotoxic by causing the appearance of necrotic lesions [57].…”

Global potential distribution prediction of Xanthium italicum based on Maxent model

“…The biological invasion has become a great challenge for human beings. Xanthium italicum Moretti is one of the most widely distributed invasive plants in the world, and its biological characteristics of easily carrying seeds make it more likely to spread widely 6 . X. italicum is an annual herbaceous plant of the genus Xanthium in the Compositae family, propagated by seeds 7 , and native to North America but has been spread to many countries and regions in Europe, Asia, and Oceania 8 , 9 .…”

Recent Advances in Alternaria Phytotoxins: A Review of Their Occurrence, Structure, Bioactivity, and Biosynthesis

“…It was suggested that the phenolic hydroxyl group played a key role in the toxicity to soybean cell culture [183]. AOH inhibited root growth of Pennisetum alopecuroides, Medicago sativa, and Amaranthus retroflexus at 1000 µg•mL −1 [184]. AME inhibited the electron transport chain of spinach chloroplasts with an IC 50 value of 29.1 µM, and inhibited the growth of Synechococcus by directly interacting with one or more of the electron carriers involved in the electron transport chain [185].…”