Abstract Peanut ( Arachis hypogaea ) is an important economic crop that is susceptible to various foliar diseases. Web blotch, which is caused by Phoma arachidicola , is one of the most serious peanut foliar diseases because it affects the leaves and results in substantial yield losses. In this study, the P . arachidicola infection process and the response of peanut plants to infection were revealed through a cytological study of resistant and susceptible peanut varieties. Conidial germination rates, appressorium formation and resistance responses, including papillae formation and the hypersensitive response (HR), were analysed at different infection stages. Notably, the basal infection response of susceptible varieties resulted in limited papillae formation and a single HR, which was followed by programmed cell death. The papillae formation frequency and HR frequency were significantly greater in the resistant varieties than in the susceptible varieties at 84 h postinoculation. The primary difference between the two resistant varieties was the superior HR of Zheng8903 compared with that of Yuhua15. The complex amphidiploid peanut genome may explain the complexity and diversity of the resistance responses. The interactions of functional orthologs should be clarified and perhaps modulated in future investigations. The results of this study revealed the differences in the resistance responses among peanut germplasm and may be relevant for the breeding of new peanut varieties highly resistant to P . arachidicola .