ARS | Publication request: Alteration in Lignin Biosynthesis Restricts Growth of Fusarium Species in Brown Midrib Sorghum

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 13, 2010
Publication Date: June 8, 2010
Repository URL: http://hdl.handle.net/10113/43486
Citation: Funnell-Harris, D.L., Pedersen, J.F., Sattler, S.E. 2010. Alteration in Lignin Biosynthesis Restricts Growth of Fusarium Species in Brown Midrib Sorghum. Phytopathology 100:671-681.

Interpretive Summary: We provided evidence that a mutation in lignin biosynthesis can prevent infection by a fungus that is commonly found in wild-type sorghum. Lignin biosynthesis mutants, bmr6 or bmr12, were used to reduce lignin content and increase cell wall digestibility. We screened field-grown grain and found a significant reduction in Fusarium fungal species that include sorghum pathogens in bmr grain. Using a molecular technique to identify Fusarium species, eleven species colonizing grain were found. Three of the most frequently found species were sorghum pathogens while three other commonly recovered species colonize sorghum without producing symptoms. The second most commonly isolated fungus from wild-type grain was not detected on bmr12 grain. The third most commonly isolated fungus, a pathogenic species had reduced colonization in bmr12 grain. Stalks of wild-type and near-isogenic bmr6 and bmr12 plants were inoculated with three sorghum pathogens: two Fusarium and one Alternaria species. Infected areas resulting on bmr6 or bmr12 plants, or both, were smaller than those on wild-type plants. We propose that one or more factors in bmr plants, resulting from lignin biosynthesis mutations, is either directly inhibitory to Fusarium species, and possibly other fungi, or results in activation of resistance mechanisms effective against these fungi.

Technical Abstract: To improve sorghum for bioenergy and forage uses, brown midrib6 (bmr) and 12 near-isogenic genotypes were developed in different sorghum backgrounds. bmr6 and bmr12 grain had significantly reduced colonization by members of the Gibberella fujikuroi species complex as compared with wild-type. Fusarium species were identified using sequence analysis of a portion of the translation elongation factor 1-a gene (TEF). The pathogens Fusarium thapsinum, Fusarium proliferatum and Fusarium verticillioides, G. fujikuroi members, were commonly recovered. Other frequently isolated Fusarium species likely colonize sorghum asymptomatically. Chi-square analyses showed that the ratios of Fusarium species colonizing bmr12 grain were significantly different from wild-type, indicating that bmr12 affects colonization by Fusarium spp. One Fusarium incarnatum/equiseti species complex (FIESC) genotype, commonly isolated from wild-type and bmr6 grain, was not detected in bmr12 grain. Phylogenetic analysis suggested that this FIESC genotype represents a previously unreported TEF haplotype. When peduncles of wild-type and near-isogenic bmr plants were inoculated with F. thapsinum F. verticillioides, or Alternaria alternata, the resulting mean lesion lengths were significantly reduced relative to wild-type in one or both bmr mutants. This indicates that impairing lignin biosynthesis results in reduced colonization by Fusarium spp. and A. alternata.