In vitro and in vivo toxicity of nano chitosan against Curvularia lunata, the causal microorganism of fruit rot and blight, a new disease of olive (O. europaea L.)

During 2019, fruit blight and rot symptoms were observed on olive ( O. europaea L.) fruits on trees grown in the Experimental Farm, Faculty of Agriculture, Sohag University, Egypt. Fungal isolates recovered from symptomatic fruits were identified as Curvularia lunata (Walker) Boedijn (two isolates) and A. alternata (Fr.) Keissl. (one isolate). Koch’s postulates were fulfilled by a pathogenicity test conducted in vitro on olive fruits wounded before inoculation with fungal isolates and incubation at 25 ± 0.2 °C in a moist chamber for a week. During incubation, we observed the development of blight and rot symptoms on fruits inoculated with both isolates of C. lunata , similar to the natural symptoms described. Conversely, A. alternata was nonpathogenic to olive fruits. PCR amplification using the specific P1 and P2 primers to C. lunata based on the Clg2p Ras protein gene sequences resulted in approx. 870 base pairs for all DNA of C. lunata analyzed, confirming the identification of C. lunata . In vitro, both chitosan nano and non-nano scale effectively inhibited mycelial growth by reducing linear mycelium and biomass and sporulation of C. lunata . In vivo, chitosan nanoscale at 2.0 mg mL −1 greatly reduced the infection and the lesion diameter of C. lunata inoculated fruits after a week and effectively induced defense-related enzyme activity of PO, PPO, and PAL. This report is the first recording of fruit blight and rots on olive caused by C. lunata , as a new disease. Also, we report the in vitro and vivo toxicity of nanoparticles of chitosan as a natural elicitor, effectively inducing defense-related enzymes against C. lunata .