Seven flavanones were identified from kino exudate of Corymbia torelliana by spectroscopic and spectrometric methods including UV, 1D and 2D NMR and UPLC-HR-MS. The study identified seven molecules, namely 3,4',5,7-tetrahydroxyflavanone (1), 3',4',5,7-tetrahydroxyflavanone (2), 4',5,7-trihydroxyflavanone (3), 3,4',5-trihydroxy-7-methoxyflavanone (4), (+)-(2S)-4',5,7-trihydroxy-6-methylflavanone (5), 4',5,7-trihydroxy-6,8-dimethylflavanone (6) and 4',5-dihydroxy-7-methoxyflavanone (7) from this eucalypt species. This is the first report of these natural products from C. torelliana kino exudate.

Traditional medicine and ecological cues can both help to reveal bioactive natural compounds. Indigenous Australians have long used kino from trunks of the eucalypt tree, Corymbia citriodora, in traditional medicine. A closely related eucalypt, C. torelliana, produces a fruit resin with antimicrobial properties that is highly attractive to stingless bees. We tested the antimicrobial activity of extracts from kino of C. citriodora, C. torelliana × C. citriodora, and C. torelliana against three Gram-negative and two Gram-positive bacteria and the unicellular fungus, Candida albicans. All extracts were active against all microbes, with the highest activity observed against P. aeruginosa. We tested the activity of seven flavonoids from the kino of C. torelliana against P. aeruginosa and S. aureus. All flavonoids were active against P. aeruginosa, and one compound, (+)-(2S)-4′,5,7-trihydroxy-6-methylflavanone, was active against S. aureus. Another compound, 4′,5,7-trihydroxy-6,8-dimethylflavanone, greatly increased biofilm formation by both P. aeruginosa and S. aureus. The presence or absence of methyl groups at positions 6 and 8 in the flavonoid A ring determined their anti-Staphylococcus and biofilm-stimulating activity. One of the most abundant and active compounds, 3,4′,5,7-tetrahydroxyflavanone, was tested further against P. aeruginosa and was found to be bacteriostatic at its minimum inhibitory concentration of 200 µg/mL. This flavanonol reduced adhesion of P. aeruginosa cells while inducing no cytotoxic effects in Vero cells. This study demonstrated the antimicrobial properties of flavonoids in eucalypt kino and highlighted that traditional medicinal knowledge and ecological cues can reveal valuable natural compounds.

Six cultivars of vegetable sovbean (Glycine max [L.] Merr.) were evaluated in the laboratory for relative levels of antibiosis to corn earworm (Helicoverpa zea [Boddie]). The cultivars evaluated were Fuji, Kim, Oakland, Peking, Sanga, and Toano. One plant introduction (PI 229.358) having known resistance to corn earworm and Essex, a commercial cultivar, were used as check plants. The biological data for antibiosis in a series of tests included larval weights. The results showed that cultivars Sanga, Peking, and Oakland were comparatively more susceptible while cultivars Fuji, Kim, and Toano exhibited a moderate level of leaf feeding resistance to corn earworm. The cultivars with moderate resistance can be useful in reducing corn earworm damage and cost of chemical control in vegetable soybean insect pest management systems.

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