Response of fusarium thapsinum to sorghum brown midrib lines and to phenolic metabolites

Authors: Funnell-Harris, Deanna; Sattler, Scott; Pedersen, Jeffrey

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2014
Publication Date: 9/11/2014
Publication URL: http://handle.nal.usda.gov/10113/59573
Citation: Funnell-Harris, D.L., Sattler, S.E., Pedersen, J.F. 2014. Response of fusarium thapsinum to sorghum brown midrib lines and to phenolic metabolites. Plant Disease. 98:1300-1308.

Interpretive Summary: Sorghum was bred for cellulosic bioenergy uses by incorporating two genes that resulted in reduced lignin content of the sorghum biomass. Using a newly developed technique, the normal lines and low lignin lines were tested for resistance to Fusarium stalk rot, which can cause lodging. The results showed that the low lignin lines were as resistant as the normal lines. Stem infections can cause breakage and loss of the head. Stems of newly identified low lignin lines were inoculated with the stalk rot fungus. These new low lignin lines also were as resistant as the normal line. One of the new low lignin lines was even more resistant than the normal line. To identify possible plant sources of resistance, the stalk rot fungus was grown on chemicals commonly found in stems of low lignin sorghum. Surprisingly, this fungus was not affected in growth by these chemicals, which implies that there are other factors involved in the resistance seen in low lignin plants. Eight other sorghum pathogens were also grown on these chemicals and they were all inhibited by at least one of them. Although the Fusarium stalk rot fungus may not be controlled by the tested chemicals found in low lignin sorghum, the other eight pathogens may be able to be controlled by them.

Technical Abstract: Sorghum lines were bred for reduced lignin for cellulosic bioenergy uses, through the incorporation of brown midrib (bmr) bmr6 and/or 12 into two genetic backgrounds, either as single or double mutant lines. These lines were assessed for resistance to Fusarium thapsinum stalk rot, a cause of lodging. This assay showed that the bmr lines were as resistant to F. thapsinum as near-isogenic wild-type lines. Peduncles of newly identified bmr lines from an ethyl-methanesulfonate-mutagenized population, inoculated with F. thapsinum, were as resistant as the wild-type line, BTx623. One bmr line had significantly smaller mean lesion lengths than BTx623. Growing F. thapsinum on medium with ferulic, vanillic, sinapic, syringic and caffeic acids, phenolic compounds derived from the lignin pathway, indicated that F. thapsinum was tolerant to all these compounds. However, eight other fungi associated with sorghum were grown in the presence of these phenolic acids and ferulic acid inhibited the growth of all eight fungi. Most of the phenolics inhibited Fusarium verticillioides and Fusarium proliferatum. For some sorghum pathogens, the accumulation of phenolic metabolites in bmr plants may inhibit their growth, while other factors appear to be involved in resistance to F. thapsinum.