Antioxidant, Antifungal and Aphicidal Activity of Triterpenoids Spinasterol, 22,23-Dihydrospinasterol From Colocynthis (Citrullus Colocynthis L.) Leaves

Terpenoids from natural plants resources are valuable for diverse biological activities which exhibited important part in medical and agrochemicals industry. This study aimed to assess the antioxidant, antifungal and aphicidal activity of a mixture of Spinasterol, 22,23-dihydrospinasterol from Citrullus colocynthis leaves. 1, 1-diphenyl-2-picrylhydrazyl (DPPH) was used to assess the antioxidant activity whereas, antifungal activity was tested by mycelium growth inhibition assay on three pathogenic fungi Magnaporthe grisea, Rhizoctonia solani and Phytophthora infestans. Aphicidal activity against adults of Myzus persicae was also determined via In-vitro and In-vivo assays. The outcome of the study exposed that Spinasterol, 22, 23-dihydrospinasterol afforded moderate antioxidant activity even at lower concentrations i.e. 19.98, 31.52, 36.61 and 49.76% at 0.78, 3.0, 12.5 and 50µgmL− 1 respectively. However, reasonable fungicidal activity of Spinasterol, 22; 23-dihydrospinasterol was recorded as being EC50 values 129.5 and 206.1µgmL− 1 against R. solani and M. grisea respectively. On the other hand, Boscalid and Carbendazim being a positive control proved highly effective against all fungi except for M. grisea and P. infestans with EC50 values 868 and 272109µgmL− 1 respectively. The significant insecticidal activity was afforded via residual as well as greenhouse assay being LC50 values as 42.46, 54.86, 180.9 µgmL− 1 and 32.71, 42.46 and 173.8µgmL− 1 at 72, 48 and 24 h respectively. Moreover, antioxidant activity of Spinasterol, 22,23-dihydrospinasterol presented strong positive correlation versus antifungal and insecticidal activity. Spinasterol, 22,23-dihydrospinasterol possess good antioxidant and aphicidal activity with moderate fungicidal activity which could be a suitable candidate as an alternative to synthetic pesticidal agents.

Field Evaluation of Native B. thuringiensis Isolates Against Aphids (Aphis fabae)

Objectives: The purpose of this study was to evaluate the aphicidal activity of native Bacillus thuringiensis (Bt) strains. Methods: Soil samples of Provinces 2 and 3 of Nepal were collected randomly for isolation of Bt by acetate selection method. Bt were identified by observing insecticidal crystal proteins (ICPs) by Commassie Brilliant Blue (CBB) staining technique. Aphicidal activity of 12 B. thuringiensis isolates was evaluated by two processes. The preliminary screening was done by spraying the suspension containing the spore and ICPs mixture in Phaseolus species heavily infested with black aphids (Aphis fabae) in fi elds. The second process (selective bioassay) was done by counting the number of aphids (nymphs, instar, winged, wingless) before and after spraying 5ml of suspension containing the spore and ICPs mixture on the leaf or on the beans pods surface infested by Aphids. The mortality percentage of Aphids after treatment was calculated on the 4th day, by counting the live aphids and the result was recorded. Results: Preliminary screening for aphicidal activity revealed that 4 isolates ML5(1), CW1(1), SN2(1) and MP2(1) producing spherical crystal protein, showed 100% mortality against nymphs, instar, winged and wingless Aphids. Isolates were effective in controlling the Aphid (Aphis fabae) within 4 days and the part of the plant that was sprayed becomes free of Aphids. Selective bioassay of native isolate MP3(3) was most effective in killing 95.83% of aphids followed by CW2(1), 85.71%, ML5(1), 77.34%, SN3(1), 72.72%, CW1(1), 70.21%. Conclusion: This study revealed that indigenous Bacillus thuringiensis of Terai region of Nepal are effective in controlling Aphids.

Spinasterol, 22,23-Dihydrospinasterol and Fernenol from Citrullus Colocynthis L. with Aphicidal Activity against Cabbage Aphid Brevicoryne Brassicae L.

Brevicoryne brassicae is a problematic pest in cabbage and other field crops. Synthetic pesticides are used to control this pest, but they are injurious for human health and the environment. The present study aimed to purify and identify the active compounds from Citrullus colocynthis leaves with an appraisal of their efficacy against B. brassicae. Separation and purification were performed via different chromatographic techniques. Molecular analysis and chemical structures were recognized by mass spectrum (MS) and nuclear magnetic resonance (NMR), respectively. Moreover, in vitro and in vivo aphicidal activity was assessed using various concentrations, i.e., 6.25, 12.5, 25 and 50 µg/mL at 12, 24, 48 and 72 h exposure. The outcome shows that mass spectrum analyses of the purified compounds suggested the molecular formulae are C30H50O and C29H50O, C29H48O. The compounds were characterized as fernenol and a mixture of spinasterol, 22,23-dihydrospinasterol by 1H-NMR and 13C-NMR spectrum analysis. The toxicity results showed that the mixture of spinasterol and 22,23-dihydrospinasterol showed LC50 values of 32.36, 44.49 and 37.50 µg/mL by contact, residual and greenhouse assay at 72 h exposure, respectively. In contrast, fernenol recorded LC50 values as 47.99, 57.46 and 58.67 µg/mL, respectively. On the other hand, spinasterol, 22,23-dihydrospinasterol showed the highest mortality, i.e., 66.67%, 53.33% and 60% while, 30%, 23.33% and 25% mortality was recorded by fernenol after 72 h at 50 µg/mL by contact, residual and greenhouse assay, respectively. This study suggests that spinasterol, 22,23-dihydrospinasterol are more effective against B. brassicae which may be introduced as an effective and suitable substitute of synthetic chemical pesticides.