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Wild tomato species in Solanum Section Lycopersicon often exhibit two types of reproductive barriers: self‐incompatibility (SI) and unilateral incompatibility or incongruity (UI), wherein the success of an inter‐specific cross depends on the direction of the cross. UI pollen rejection often follows the ‘SI × SC’ rule, i.e. pistils of SI species reject the pollen of SC (self‐compatible) species but not vice versa, suggesting that the SI and UI pollen rejection mechanisms may overlap. In order to address this question, pollen tube growth was measured after inter‐specific crosses using wild tomato species as the female parents and pollen from cultivated tomato (Solanum lycopersicum). Two modes of UI pollen rejection, early and late, were observed, and both differed from SI pollen rejection. The structure and expression of known stylar SI genes were evaluated. We found that S‐RNase expression is not required for either the …