Optimization of nanofibrillation degree of chitin for induction of plant disease resistance: Elicitor activity and systemic resistance induced by chitin nanofiber in cabbage and strawberry.

Chitin has not been extensively used in agriculture owing to its handling difficulties despite its utilizable functions such as induction of disease resistance and growth promotion in plants. Chitin nanofiber (CNF), which has an elicitor activity to induce plant disease resistance, can be handled like a water-soluble material, because of its high dispersibility. To determine the potential use of CNF in agriculture, the nanofibrillation degree of chitin for elicitor activity and its effect on the disease resistance against pathogens were examined in cabbage and strawberry plants. The similarity in thickness and length of CNF to that of polymeric chitin was sufficient to induce elicitor activity in both plants. Cabbage and strawberry plants, which were grown in a mixture of soil and CNF with optimized specification, challenged with fungal pathogens showed a reduction in the number of spots caused by Alternaria brassicicola and lesion size by Colletotrichum fructicola, respectively. Gene expression analysis revealed that the defense-related genes in cabbage plant grown in CNF-containing soil were significantly upregulated before and after pathogen infection. These results indicate that CNF can systemically induce disease resistance in cabbage and strawberry plants and is a promising natural-based material to control diseases in cultivated plants.