Dynamics of solute/matric stress interactions with climate change abiotic factors on growth, gene expression and ochratoxin aA production by Penicillium verrucosum on a wheat-based matrix

Penicillium verrucosum is responsible for ochratoxin A (OTA) contamination of temperate cereals during harvesting and storage. Inoculum comes from soil and crop debris. This study examined the effect of temperature (25 vs 30 °C), CO2 (400 vs 1000 ppm) and matric and solute stress (-2.8 vs -7.0 MPa) on (i) growth, (ii) key OTA biosynthetic genes and (iii) OTA production on a milled wheat substrate. Growth was generally faster under matric than solute stress at 25 °C, regardless of CO2 concentrations. At 30 °C, growth of P. verrucosum was significantly reduced under solute stress in both CO2 treatments, with no growth observed at -2.8 MPa (=0.98 water activity, aw) and 1000 ppm CO2. Overall, the growth patterns under solute stress was slower in elevated CO2 than under matric stress conditions when compared with existing conditions. The otapksPV gene expression was increased under elevated CO2 levels in matric stress treatments. There was fewer effects on the otanrpsPV biosynthetic gene. This pattern was paralleled with the production of OTA under these conditions. This suggest that P. verrucosum is able to actively grow and survive in both soil and on crop debris under three way interacting climate-related abiotic factors. This resilience suggests that they would still be able to pose an OTA contamination risk in temperate cereals post-harvest.