Purpose:In this study, we observed the effect of exogenous melatonin on the proliferation and pathogenicity of Alternaria alternata, judged the biological function of melatonin on Alternaria alternata, and found the key genes of melatonin regulating Alternaria alternata traits at the transcription level by RNA SEQ, and preliminarily revealed its mechanism of action. Methods:SNA medium with melatonin concentration of 50, 100, 500, 1000 and 1500 µ m was prepared and 30 ml plate was made. Take sterilized circular filter paper with a diameter of 1 cm, add 100 UL 50 CFU / cm3 spore suspension, transfer to SNA medium center, and culture upside down for 7 days Results:In this study, 20 metabolic pathways with the most significant KEGG enrichment were selected from the four control groups by P value analysis (Fig. 9). In 500 µ m vs control group, DEGs were mainly enriched in ribosome, glyoxylic acid and dicarboxylic acid metabolism pathways. In 1500 µ m vs control group, the metabolic pathways such as glyoxylic acid and dicarboxylic acid metabolism, valine, leucine and isoleucine degradation, ketone body synthesis and degradation, terpenoid main chain biosynthesis were the most significant in 500 µ m vs 1500 µ m, DEGs were mainly enriched in eukaryotic ribosome biosynthesis and RNA polymerase pathway 500 µ m vs 1500 µ M Compared with the control treatment, DEGs were significantly enriched among the three groups, and the pathways were rich, such as amino acid metabolism, glyoxylic acid and dicarboxylic acid metabolism, valine, leucine and isoleucine degradation, glyceride metabolism, glycolysis / gluconeogenesis, ABC transporter and so on. Conclusions:Nine DEGs related to the development and pathogenesis of streptozospora were obtained by transcriptional sequencing. The results showed that melatonin involved aflatoxin biosynthesis (sld1 and sld2, s-adenosine-l-methionine dependent methyltransferase synthesis), MAPK signal pathway (GLP), linoleic acid metabolism (HP1), heme peroxidase synthesis )The results showed that the metabolism of selenium (THR), protein processing in endoplasmic reticulum (KHP, 30kda heat shock protein synthesis), glycolysis / glycometagenesis (PPL), and synthesis of non reductive poly ketoacetase (NPS) and heme peroxidase (HP2) were also studied. Among them, THR is related to proliferation regulation [49], sld1, sld2, NPs and ppl are related to pathogenicity , GLP is related to colony growth and pathogenicity, KHP is related to stress , HP1 and HP2 are related to antioxidant activity . Overall design: The colony of Alternaria alternata treated with 0, 500 and 1500 µ m melatonin was used as experimental material