Screening for resistance to Fusarium ear rot disease in the USA maize inbred line collection using a rolled towel assay.

Fusarium verticillioides is the causal agent of Fusarium ear rot, it is associated with disease at all stages of maize development, also causing symptomless endophytic infection. This fungus produces fumonisins, a family of mycotoxins that contaminate grain, threatening human and animal health. Genetically resistant maize hybrids are necessary to control Fusarium ear rot and reduce fumonisin contamination. Resistance is under polygenic control and so far no immune genotypes have been found. Previous inbred evaluations were performed in field trials infecting ears after silking and evaluating the ear rot at harvest maturity. Resistance during seed germination is part of the plant-pathogen interaction and so far this aspect has not been investigated. In this study the 267 corn inbreds of the maize association population (Plant J. 2005 Dec; 44(6):1054-64) were screened using a Rolled Towel Assay to evaluate the resistance of maize kernels against F. verticillioides. Surface disinfected seeds were placed on germinating paper towels, inoculated with F. verticillioides conidial suspension and rolled up. Non-inoculated towels were used as control. Disease severity was evaluated with a 1 (healthy kernel) to 5 (complete rotting) scale depending on symptoms of kernel colonization after 7 days of incubation at 25°C, germination percentages, seedling length and weight were recorded for each seedling. The majority of the lines have a disease severity mean between 2,5-3,5 and few lines fall in the lower or higher infection classes. Disease severity evaluation reveals different degrees of susceptibility and responses in maize inbreds, suggesting possible sources of genetic resistance. These phenotypic data will be used to perform a Genome Wide Association Study (GWAS) using a combined set of 47k array-based SNPs (PLoS ONE 6(12): e28334) plus and additional 50k+ derived from GBS in order to dissect genes related to Fusarium resistance.