Isolation, identification and characterization of labdane diterpenoids with antifungal/anti-TMV activities from Nicotiana glutinosa

Nicotiana glutinosa is a tobacco plant abundant in labdane diterpenoids. This study determined the composition and contents of the main labdane diterpenoids in N. glutinosa and evaluated their bioactivities and corresponding structure-activity relationship (SAR) in anti-Tobacco Mosaic Virus (TMV) and anti-phytopathogenic fungi. Eight labdane diterpenoids and one sesquiterpene were isolated , among which 2α/2β-hydroxymanool, manoyl oxide, and 13-epimanoyl oxide were identified from tobacco for the first time. The labdane diterpenoids were most abundant in flowers and upper-middle leaves, with a total amount of 1260–1457 μg/g FW dominated by sclareol (accounting for 50% of the total labdane diterpenoids), manool, and its derivatives. The crude extract and separated fractions Fr.3/Fr.4 exhibited promising bioactivities in inhibiting TMV, gray mold, and apple valsa canker. Sclareol and labdenediol exhibited TMV inactivation rates of 66.37% and 55.28%, respectively, at 200 μg/mL. Sclareol, 2α/2β-hydroxymanool, and labdenediol inhibited the growth of Botrytis cinerea by 72.37–80.20% in vitro at 20 μg/mL and by 68.14–83.60% in vivo at 100 μg/mL, which was superior/equivalent to pyrimethanil. Sclareol and 13-epimanoyl oxide inhibited the growth of Valsa mali by 98.09% and 94.60%, similar to the activity of carbendazim. SAR revealed that the anti-TMV activity of labdane diterpenoids may be correlated with the C−8 hydroxylation, while their antifungal activity depended on the amphiphilic balance between hydrophobic ‌parent nucleus and polar groups. This study provides a resource for isolating plant-derived antiviral/fungicidal compound and molecular templates for pesticide design according to the SAR references.