Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses.

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H2O2, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Characterization of a Novel Chitinase from Sweet Potato and Its Fungicidal Effect against Ceratocystis fimbriata.

Black rot, caused by Ceratocystis fimbriata, is a destructive disease of sweet potatoes (Ipomoea batatas). In this study, a novel chitinase (IbChiA) was screened from sweet potatoes, which showed a remarkably higher expression level in resistant varieties than in susceptible ones after inoculation with C. fimbriata. Sequence analysis indicated that IbChiA belongs to family 19 class II extracellular chitinase with a MW of 26.3 kDa and pI of 5.96. Recombinant IbChiA, produced by Pichia pastoris, displayed antifungal activity and stability. IbChiA could restrain the mycelium extension of C. fimbriata. FDA/PI double staining combined with transmission electron microscopy observation revealed the remarkable fungicidal effect of IbChiA on the conidia of C. fimbriata. The disease symptoms on the surface of slices and tuberous roots of sweet potatoes were significantly reduced after treatment with IbChiA. These results indicated that IbChiA could be used as a potential biofungicide to replace chemical fungicides.