Abstract
Rice sheath blight, caused by Rhizoctonia solani, is a globally important rice disease and the increasing resistance of this pathogen highlights the need for new active compounds against rice sheath blight. In this study, natural β-carboline alkaloids were optimized to obtain a series of 1,2,4,9-tetrahydro-3-thia-9-aza-fluorene derivatives and evaluated for their fungicidal activity and mode of action against R. solani. Of these compounds, 18 exhibited significant in vitro fungicidal activity against R. solani, with an EC50 value of 2.35 μg/mL, and was more active than validamycin A. In vivo bioassay also demonstrated that 18 displayed superior protective and curative activities as compared to validamycin A. Mechanistically, 18 not only induced the loss of mitochondrial membrane potential and accumulation of reactive oxygen species, but also interfered with DNA synthesis. Therefore, compound 18 displayed pronounced in vitro and in vivo fungicidal activity against R. solani and could be used as a potential candidate for the control of rice sheath blight.
Highlights
Rice sheath blight, caused by Rhizoctonia solani [1], is one of the most important and destructive fungal diseases in rice around the world [2], and has caused devastating losses of yield up to 50% under favorable conditions as well as decreased quality of rice [3,4]
Natural bioactive products are considered as ideal lead compounds to develop biorational alternatives compared to synthetic agrochemicals [8,9]. β-Carboline alkaloids and the saturated analogues, dihydro-β-carboline and tetrahydro-β-carboline alkaloids, are the main active components from medicinal genus Peganum, such as Peganum harmala, P. multisectum, and P. nigellastrum, which are distributed in the northwest of China [10]
Harmine (1) and its analogs 3 and 5–13 were screened for their fungicidal activity against R. solani and the results presented in Table 1 show that these three β-carboline alkaloids displayed similar fungicidal activity against R. solani, indicating that the C ring of β-carboline is attractive for further optimization
Summary
Rice sheath blight, caused by Rhizoctonia solani [1], is one of the most important and destructive fungal diseases in rice around the world [2], and has caused devastating losses of yield up to 50% under favorable conditions as well as decreased quality of rice [3,4]. A few fungicides are available and have been widely used for the control of rice sheath blight [5], such as validamycin A [6], indiscriminate fungicide usage increases the risk of pathogen resistance and harms the environment and human health [7]. The quest for highly-effective fungicides against rice sheath blight with a novel mode of action is imperative. Harmine (1), harmane (2), harmaline (3), harmalol (4), and tetrahydroharmine (5) are the representative harmala alkaloids (Figure 1), and these alkaloids have demonstrated marginal and similar fungicidal activity against several pathogenic fungi including R. solani [11,12], which implies that ring C of β-carboline is attractive for further optimization. CCHOOH3O2O;CEEOtt;;OMe; CH22COOMEte; ; C((BCCHzHH;222C))4O4CCOOOEOOt;EEtt;; 34: 35: R2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
