Penicillium verrucosum survives in soil and on cereal debris. It colonises grain during harvesting, drying and storage. There is no information on the relative tolerance of P. verrucosum to solute and matric stress in terms of colonisation, or on the biosynthetic toxin gene clusters or ochratoxin A (OTA) production. The objectives were to examine the effect of ionic and non-ionic solute and matric potential stress on (a) growth, (b) expression of two toxin biosynthetic genes otapksPV and otanrpsPV, and (c) OTA production by a strain of P. verrucosum. Optimum growth and OTA production were at -7.0 MPa (= 0.95 water activity, a_w) and -1.4 MPa (= 0.99 a_w), respectively, regardless of whether solute (Ψ_s) or matric (Ψ_m) stress was imposed. P. verrucosum was more sensitive to ionic solute stress (NaCl) with no growth at -19.6 MPa (=0.86 a_w) while growth still occurred in the non-ionic solute (glycerol) and matric stress treatments. Relative gene expression of the biosynthetic genes using PCR (RT-qPCR) showed that the otapksPV gene was expressed over a wide range of ionic/non-ionic solute stress conditions (-1.4 to -14.0 MPa; = 0.99-0.90 a_w). The highest expression was in the non-ionic Ψ_s stress treatments at -7.0 MPa (= 0.95 a_w). However, the otanrpsPV gene was significantly up regulated under Ψ_m stress, especially with freely available water (-1.4 MPa = 0.99 a_w). OTA production was significantly decreased as Ψ_s or Ψ_m stress were imposed. Limited OTA production occurred in the driest treatments under Ψ_s and Ψ_m stress respectively. The impact of these two types of stresses on the growth of P. verrucosum was quite different from that for OTA production. The results are discussed in the context of the life cycle and ecological characteristics of this species in contaminating cereals with OTA in the post-harvest phase of the cereal chain.