Cai Liang,Li Yang,Yu Shao,Xinyue Zhu,Hongliang Zhao,Biwei Chen,Wen Song,Xiangmin Song,Xiaofan Ding,Ranfeng Sun
The secondary metabolites produced by plants are important sources of fungicides with intriguing bioactivities and environmentally benign attributes (eg. low residual toxicity to mammals and readily biodegradable in soil). In this study, the dichloromethane extract of stems of Waltheria indica L. was found to exhibit broad-spectrum antifungal activity toward eight phytopathogenic fungi, particularly against carbendazim-resistant Sclerotinia sclerotiorum with inhibition rate of 100% at 500 μg/mL. Two quinoline alkaloids, antidesmone and waltherione C, were isolated and identified as fungicidal compounds by bioassay-guided isolation and spectroscopic analyses. Antidesmone displayed superior antifungal activities against eight phytopathogenic fungi to commercial botanical fungicides (osthole, carvacrol, and eugenol). Moreover, antidesmone was found to have significant negative cross-resistance with carbendazim to Sclerotinia sclerotiorum for the first time and exhibited much better antifungal activity (EC 50 = 0.60 μg/mL) against carbendazim-resistant strains than carbendazim-sensitive strain (EC 50 = 9.61 μg/mL) of Sclerotinia sclerotiorum , which was further supported by the molecular modelling result. In addition, the dichloromethane extract of the Waltheria indica stems could effectively control the development of eleven species of phytopathogenic fungi in vivo. These results suggest that Waltheria indica dichloromethane extract and antidesmone can be developed as promising broad-spectrum botanical fungicides.
Waltheria indica L. is a traditional officinal plant with many medicinal and insecticidal properties. This study established an in vitro propagation system for W. indica and evaluated the repellent activity of the compounds from in vitro-derived plants against the nematode Meloidogyne incognita . We optimized the medium for axillary bud proliferation and rooting of sterile shoots. Adventitious buds were induced from hypocotyls on Murashige and Skoog (MS) + 0.1 mg/L 6-benzyladenine (BA). MS + 1.0 mg/L 6-BA + 0.2 mg/L 1-napthaleneacetic acid (NAA) + 1.0 mg/L 2,4-dichlorophenoxyacetic acid was the best media for adventitious root induction from callus. An adventitious root suspension culture system was successfully induced and established in MS medium supplemented with 1.0 mg/L NAA, using a 1% inoculum size and a 30-day subculture interval. We isolated and identified antidesmone and trans-tiliroside from W. indica plants. They demonstrated repellent activity against J2 of M. incognita with chemotaxis index of 0.41 and 0.22, respectively, at a concentration of 10 mg/L. The relative content of antidesmone in adventitious roots cultured in liquid suspension was significantly higher than that in tissue-cultured plantlets. Exogenous supplementation of 0.05 mg/L 6-BA significantly improved the accumulation of trans-tiliroside synthesis in stems and leaves by reversing the inhibitory effect of tissue culture conditions. This study provides a theoretical basis and technical support for the large-scale propagation, germplasm improvement, and regulation of active secondary metabolite production in W. indica.
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