Pipecolic Acid‐Induced Physiological and Biochemical Changes in Maize Hamper Colletotrichum graminicola Infection

Anthracnose, caused by Colletotrichum graminicola , is an important foliar disease on maize. We hypothesised that pipecolic acid (PA) could boost the defence of maize leaves against fungal infection. An in‐depth analysis of the photosynthetic apparatus, quantification of malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and superoxide anion radical (O 2 •− ) as well as changes in the expression of genes involved in both host defence and the antioxidant metabolism was investigated. Leaves of plants non‐sprayed (−PA) or sprayed (+PA) with PA were challenged with C. graminicola . Reduced anthracnose symptoms and less production of MDA, H 2 O 2 and O 2 •− occurred for +PA plants. The +PA and infected plants displayed higher values for F v / F m , Y(II) and Y(NPQ) and greater concentrations of chlorophyll a + b and carotenoids. Expressions of genes involved in PA and N ‐hydroxy‐PA synthesis ( ALD1 and FMO , respectively) were significantly up‐regulated for infected +PA plants from 2 to 16 days after inoculation (dai) compared to infected −PA plants. For infected +PA plants, NPR1 expression was kept significantly higher from 4 to 12 dai, but only at the advanced stage of fungal infection (at 16 dai) for −PA plants. Genes related to maize defence ( Bx1 , IGL , CHS02 , PR1 , POX and CHI ) and the antioxidative metabolism ( CAT , SOD and GR ) were greatly up‐regulated for +PA infected plants compared to infected −PA plants. These findings strongly suggested the positive effect of PA in boosting maize resistance against infection by C. graminicola , which was linked to the preservation of the photosynthetic apparatus and a robust antioxidative metabolism.