Abstract：Late blight is an important disease destroying tomato production．Previous studies have shown that Ph-2 gene presented age-related resistance against late blight in tomato．In this study，we used comparative transcriptome analysis to identify the differentially expressed genes at 0 h，8 h，24 h and 48 h respectively after inoculation of Phytophthora infestans between two seedling stages．The results showed that there was no significant difference in the expression levels of Ph-2 gene and other typical disease resistance genes between the three-leaf stage seedlings and the six-leaf stage seedlings at 0-48 h after inoculation．The expression difference of peroxidase gene Solyc01g006290 and Solyc02g087110 between the two seedlings maybe one of the causes for the age-related resistance．The expression level of Solyc01g006290 gene in sixleaf stage seedlings from 0-48 h after inoculation was always significantly higher than that in three-leaf stage seedlings．Solyc01g006290 gene positively regulates lignin synthesis and plays an important role in cell wall strengthening．There was no significant difference in the expression level of Solyc02g087110 gene between the three-leaf stage seedings and six-leaf stage seedlings at 0 h after inoculation，but the expression level of the gene in the three-leaf stage seedlings is greatly down-regulated and significantly lower than that in the six-leaf stage seedlings at 8-48 h after inoculation．Besides，the difference in the expression of genes in salicylic acid and ethylene signal transduction pathways between the two seedlings may also be one of the reasons for the agerelated resistance．Our result lays the foundation for the durable resistant breeding against late blight in tomato．
