Nano selenium enhanced tomato resistance to leaf mold via activating salicylic acid defense pathways and regulating metabolic profiles as well as improved plant growth

Disease infection seriously threatens the healthy growth of tomatoes. In recent years, using nanomaterials to suppress crop disease damage has become a hotspot in agriculture. As an emerging nano-material, nano-selenium has been widely reported for improving crop growth and saving the damage caused by stresses such as pathogens and heavy metals on plants. This study investigated the control of tomato leaf mold (Cladosporium fulvum) by applying nano-Se (5/10/25 mg L-1) on tomato seedlings and explored related mechanisms. We found: (i) Nano-Se applying (especially 10 mg L-1) significantly inhibited tomato leaf mold and reduced disease severity of seedlings (52.84%, 14 days after inoculation). This was because nano-Se significantly promoted the accumulation of salicylic acid (SA) through up-regulating biosynthesis genes expression by significantly up-regulating the gene expression related to MAPK cascade and calcium signaling. This thereby induced the genes expression (NPR1, TGA2/1/5, WRKY33, WRKY70 and WRKY54) of SA signaling pathway, enhancing resistance-genes (PR1/2/3) transcription and elevating antioxidant and resistance-related indicator levels, ultimately activating systemic acquired resistance (SAR) in tomato. Nano-Se also promoted jasmonic acid (JA) signaling pathway. In addition, metabolomic analysis indicated nano-Se promoted phenolic compounds from the phenylpropane pathway (α-tocopherol, chlorogenic acid and ferulic acid), polyamines, GABA and various amino acids accumulation of tomato seedlings, which also supported the above results. (ii) Nano-Se promoted the growth of tomato seedings by enhancing photosynthesis and increasing auxin level. Compared to chemical fungicides, these findings suggested nano-Se provided a more promising and sustainable approach for managing diseases such as leaf mold and improving tomato plant growth.