Chitosan Oligosaccharides–Triggered Innate Immunity Contributes to Oilseed Rape Resistance against Sclerotinia Sclerotiorum

Chitosan oligosaccharides (collectively, oligochitosan, or COS) are considered to be potent plant immunity elicitors. In this article, the induction of resistance to Sclerotinia sclerotiorum in Brassica napus L. var. Huyou 15 by COS is studied. Even though COS (50 μg mL−1) did not affect radial growth of this pathogen in vitro, it reduced the disease symptoms in vivo relative to control plants. The disease control rates were 25.8%, 41.4%, 57.1%, 68.7%, and 48.8% with COS pretreatment 0, 24, 48, 72, and 96 h before S. sclerotiorum inoculation, respectively. Specific binding of COS to B. napus epidermis cells was validated by competition experiments. Simultaneously, it was observed that COS induced bursts of cytosolic Ca2+, nitric oxide (NO), and hydrogen peroxide (H2O2). NO and H2O2 inhibitors were used to prove the interaction between NO and H2O2. Furthermore, treatments of B. napus with NO and H2O2 inhibitors reduced the induction effect of the jasmonic acid–ethylene (JA/ET) signaling marker BnPDF1.2 by COS, indicating that NO and H2O2 participate in COS-induced JA/ET signaling. In conclusion, this article provides a comprehensive study of the effect and mechanism of COS-induced resistance to S. sclerotiorum in B. napus.