PPIG and viral infectious disease: Based on this observation, we systematically investigated expression stabilities of eight widely used (including ACT11, TUA5, CYP, EF1B, TUA4, TUB4, EF1A and ACT2/7) and one recently reported (UKN2) reference genes under viral infection and stresses of darking, salinity and drought, with the objective of identifying those which provide stable expressions in each of the environments assessed.