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Abstract

Recent epidemics of northern leaf blight (NLB) on brown midrib (BMR) silage corn hybrids led to the hypothesis that the BMR alleles may enhance vulnerability to fungal diseases. BMR lines have mutations in genes that influence lignin content, which is desirable in silage corn because of its greater digestibility for ruminants. These genes are part of the phenylpropanoid pathway, which plays a role not only in structural support, but also plant defense. To date, six brown midrib mutants have been described in maize, with four of them defined to the gene level. In this study, we investigate the role of the brown midrib genes as candidate genes for resistance to multiple diseases in maize through disease phenotyping and genic association analysis. Several brown midrib genes are near to or within QTL intervals for NLB. Field inoculation of bm1, bm2, bm3 and bm4 mutant lines with the NLB, Stewart’s wilt and grey leaf spot pathogens indicated that the mutants are highly susceptible to all three foliar diseases. Natural genetic variation at bm2 was associated with NLB and GLS resistance in the 282-line maize diversity panel, allelic variation at bm1 was associated with southern leaf blight. Understanding the disease vulnerabilities of BMR maize is important for resistance breeding and complementary disease management strategies.