The structures of the butenolides 1 and 2, isolated from the endemic plants Hortonia floribunda, H. angustifolia, and H. ovalifolia, collected in Sri Lanka, have been elucidated by spectroscopic analysis. These compounds exhibited potent mosquito larvicidal activity against the second instar larvae of Aedes aegypti.
Fruit rot caused by Aspergillus niger is a major postharvest problem in wood-apple, Feronia limonia Swingle (syns. F. elephantum Correa; Limonia acidissima L.; Schinus limonia L.[Rutaceae]). The effect of four Generally Recommended As Safe (GRAS) compounds-sodium bicarbonate, calcium chloride, citric acid and sodium benzoate-in different concentrations was evaluated on mycelium growth and spore germination. The effectiveness of the compounds was investigated on inoculated and naturally infected fruits. Sodium bicarbonate (4%) completely inhibited the mycelial growth and spore germination. Fruits that were first inoculated and then treated with 4% sodium bicarbonate, or the reverse, gave 53.6% and 98.4% disease reduction, respectively. Non-treated control fruits were diseased completely 3 days after inoculation. Sodium bicarbonate treatment on naturally infected fruits controlled the disease by 100% and extended the storage life up to 28 days at 27±2°C and 65-70% r.h. Sensory attributes of the treated fruits did not change during storage.
The new hexahydroazulenones hortonones A (1) to C (3) were isolated from the leaves of three representative species of the endemic Sri Lankan genus Hortonia that belongs to the family Monimiaceae. Hortonones A (1) and B (2) have the unprecedented rearranged hortonane sesquiterpenoid carbon skeleton, and hortonone C (3) has the unprecedented rearranged and degraded 13-norhortonane skeleton. Hortonone C (3) exhibited in vitro cytotoxicity against human breast cancer MCF-7 cells at 5 μg/mL.
Rice husk is a natural Silicon (Si) source. This study evaluated the effect of rice husk in two different forms; ground rice husk (GRH) and rice husk ash (RHA) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora sp. Rice husk was added to the growing medium to achieve the final concentration of 200 mg Si /kg soil. Si accumulation in leaves, disease severity, plant growth parameters, cuticle-epidermal layer thickness, chlorophyll content, total phenolic content, peroxidase (POD) and polyphenol oxidase (PPO) activity of leaves were measured. Husk treatment lowered the downy mildew severity significantly (p < 0.05) in leaves although the difference between the effects of two husk forms was insignificant. Numbers of leaves, flowers and fruits in husk-treated plants were significantly higher (p < 0.05) than those in control plants. Cuticle-epidermal layer thickness in GRH, RHA-treated and control plants were 16.8 ± 1.21, 18.2 ± 0.98 and 13.2 ± 1.27 µm respectively. Total phenol content, POD, PPO activity and chlorophyll content in rice husk-treated plants were significantly (p < 0.05) higher than that of control plants. The enhanced disease resistance in rice husk-treated plants appears to be positively associated with the higher accumulation of silicon and Si-enhanced phenolic content and increased activity of PPO and POD enzymes in leaves.
Effect of soluble silicon (Si) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora cubensis was tested using three concentrations of liquid potassium silicate (100, 200, 300 mg Si/kg) added to the growing medium containing top soil, compost and sand. Disease severity, plant growth parameters, silicon accumulation on leaves and cuticle-epidermal layer thickness of transverse sections of leaves were measured. Si treated plants exhibited less disease severity than that of control plants and 200 mg Si/kg treatment resulted in highly significant disease suppression (37 -53% reduction against controls). The suppression of the disease strongly correlated with the Si accumulation in leaves. Cuticle-epidermis thickness was higher in Si-treated leaves (17.2 -21.3 µm) against non-treated (10.3 -13.81 µm). Numbers of leaves, flowers or fruits in Si treated plants were significantly higher (p < 0.05) than control plants except in 300 ppm Si level. Structural changes created by Si may at least be partly responsible for reducing the fungal disease severity in bitter gourd leaves.
The tetracyclic sesquiterpene, ishwarane, was isolated from the leaves of the representative species of the genus Hortonia, H. angustifolia, H. floribunda and H. ovalifolia collected in Sri Lanka. The complete 2D NMR assignments are reported. Ishwarane exhibited antifungal activity against Cladosporium cladosporioides.
The dichloromethane extracts of the leaves, stem bark, bark and the roots of the three species of the primitive endemic genus Hortonia, H. angustifolia, H. floribunda and H. ovalifolia, collected from nine geographical locations ranging from lower elevations (84-420 m) to higher (2000 m) showed comparable HPLC profiles and mosquito larvicidal and antifungal activities; protein analysis of the leaves of the three species of Hortonia showed identical peaks and bands. The two major metabolites (4S)-4-methyl-2-(11-dodecynyl)-2-butenolide (2) and (4S)-4-methyl-2-(11-dodecenyl)-2-butenolide (3), which were previously reported from all three plants, showed potent larvicidal activities. Compound 2 was excessively high in the extracts of the stem bark and the roots of all three species amounting to approximately 38 and 60%, respectively. A minor new butenolide (4), (4S)-4-methyl-2-((2R)-hydroxy-11-dodecenyl)-2-butenolide, with much reduced larvicidal activity and ishwarane (1), which showed antifungal activity, were also isolated from all three plants. Treatment of compound 2 with H(2)/Pd-C afforded the completely reduced compound 5, which showed no larvicidal activity, indicating that unsaturation in both 2 and 3 is necessary for their bioactivity. The foregoing evidence showed that there are major similarities between the three species of Hortonia.
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