Induction of Chitinase and Brown Spot Disease Resistance by Oligochitosan and Nanosilica–Oligochitosan in Dragon Fruit Plants

The brown spot disease caused by Neoscytalidium dimidiatum fungus on dragon fruit plants ( Hylocereus undatus ) is an extremely serious disease. Oligochitosan (OC) and nanosilica ( n SiO 2 ) have been considered as effective plant elicitors. In this study, OC with Mw of 3000, 5000, and 7000 g/mol was prepared by γ -irradiation and n SiO 2 with size ~ 45 nm was synthesized from rice husk. Mixture of n SiO 2 –OC was prepared by dispersing n SiO 2 in OC solution. The resistant effect against brown spot disease on dragon fruit plants was assessed by measuring the induced chitinase enzyme activity and the disease severity after spraying OC, n SiO 2 –OC and inoculating fungus. The results showed that all OC enhanced chitinase induction and reduced disease severity compared with control, and the OC ~ 3000 g/mol exhibited the highest activity. The n SiO 2 –OC also exhibited similar effect as OC and n SiO 2 , but it was more effective than individual OC or n SiO 2 from 120 h onward.