Dynamic of water activity in maize hybrids is crucial for fumonisin contamination in kernels

The dynamic of water activity (aw) and humidity (h) of maize (Zea mays L.) kernels and their relevance for fumonisin (FUM) accumulation in kernels was studied in 10 commercial hybrids grown in 5 locations of North Italy, in 2007 and 2008. The dynamic of both aw and h in maize kernels was different in diverse hybrids and was accurately described by monomolecular and linear regression, respectively, using degree-days (base 0 degrees C) accumulated between female flowering and harvest as an independent variable (R2=0.61-0.96, depending on the hybrid). FUM contamination at harvest was predicted by using aw as an independent variable in a logistic regression which provided 67% of correct prediction of cases with FUM >=4000 micro g/kg of kernel; accuracy of prediction increased to 72% by using both aw and ECB severity as independent variables. The use of h as independent variable provided 71% correct predictions, but specific correction factors were necessary for each hybrid. Results showed that "slow dry down" hybrids were more prone to FUM accumulation, irrespective of their season length. The identification of factors able to drive aw dynamic in maize kernels and their genetic bases may then provide a crucial contribution in breeding maize for resistance to FUM contamination.