Location: Wheat, Sorghum and Forage Research2010 Annual Report
1a. Objectives (from AD-416)
The long-term objectives of this project are the development of sorghum (Sorghum bicolor) germplasm lines with improved bioenergy, feed, and food value, and the elucidation of genetic, biochemical, and biological factors impacting these characters. Over the next five years, the following specific objectives will be addressed: 1) Identify and evaluate genes to improve sorghum for bioenergy, food, and feed traits, 2) Develop a better understanding of genes and fundamental mechanisms controlling cell wall formation and energy availability, and 3) Develop molecular and other technologies for monitoring sorghum fungal pathogens and determine the effects of sorghum genetic modification for bioenergy on pathogen populations.
1b. Approach (from AD-416)
The project utilizes a diverse set of technologies and approaches that are best delineated by objective: Objective 1 will be addressed primarily using traditional whole-plant plant breeding techniques, animal feeding trials, and established laboratory methods for assessment of feed and bioenergy value. Objective 2 will be addressed using current molecular and biochemistry technologies including PCR, RT-PCR, HPLC, microarrays, GC-MS. Objective 3 incorporates both field-based experiments and current molecular biology technologies. All experiments will utilize sound statistical designs to allow hypothesis testing at established levels of probability.
3. Progress Report
1a. Data describing the effect of bmr-12 on grain sorghum and steer performance was analyzed, and data on the effect of bmr-12 silage on dairy performance was summarized. An article describing the effect of stacked bmr genes on ETOH was published. 1b. Backcrossing to male-sterilize selected elite B-lines was continued and S4 lines still segregating for waxy alleles were identified. 1c. Backcrossing and selfing of high energy and high starch content introductions into elite backgrounds was continued. 2a. Expressed Bmr12 (COMT) in E. coli and made site-directed mutation for bmr12 alleles. In collaboration with the National Genome Resource Center, Santa Fe, NM, detected SNPs within transcripts from the stalk between wild-type and bmr mutant lines. 2b. Demonstrated that promoter elements were not conserved within lignin biosynthetic genes. 3a. Conducted assays to measure inhibition rates of sorghum grain pathogens grown on different semi-selective medium. Isolated crude preparations of a toxin from Curvularia species; established genotype specificity in production. Established three loci for genotyping of Fusarium spp. and have sequenced the three loci from over 200 isolates. Discovered a new genotype within the Fusarium incarnatum/F. equiseti species complex. Found six species of Alternaria spp. in grain grown in Nebraska and Texas, four of which have never been reported on sorghum, and Embellesia spp., which also has not been previously reported on sorghum. Paper describing Fusarium spp. epidemiology in bmr grain published. 3b. Screening of grain from near isogenic plant color lines for Alternaria, Fusarium and Curvularia spp. to be completed by end of FY2010. 3c. Established conditions for stalk rot inoculations by Fusarium verticillioides. Assay conditions for inoculation by Macrophomina phaseolina are being established and to be completed by end of FY2010. Three repetitions to screen wild-type, bmr6, bmr12 and bmr6, bmr12 double mutant lines in two genetic backgrounds for resistance to stalk rot by Fusarium thapsinum to be completed by end of FY2010. 3d. Molecular genetic characterization of select isolates with genes for antibiotic production continued. Paper describing microbial numbers and biochemical and genetic characterization of fluorescent Pseudomonas associated with sorghum in growth-chamber and field studies accepted for publication.
1. Singular and stacked brown midrib 6 and 12 modify lignocellulosic chemistry. Brown midrib genes were introduced into the grain sorghum hybrid AWheatland x RTx430 by ARS researchers at Lincoln, NE, to reduce lignin content and improve digestibility of stalk residues following grain harvest for use as a bioenergy or livestock feedstock. Impacts of the genes bmr6, bmr12 and the bmr6bmr12 “stacked” double mutant on sorghum biomass composition and whole-plant physiology were assessed in a two year field study. The lignin content of the stacked stalk residue was further reduced compared to bmr6 or bmr12, but it had digestibility comparable to bmr12 stalk. Analysis of stalk carbohydrate composition indicated that bmr12 had modestly increased amounts of cellulose, glucoarabinoxylan and soluble sugars. Together these results indicate that bmr12 had broader effects on stalk composition than bmr6 or stacked hybrid, and this increase in carbohydrates in bmr12 is another potential positive effect for downstream applications. This body of work has demonstrated that sorghum brown midrib mutants have reduced lignin and increased biomass digestibility, while having a minor impact on plant fitness and yield in hybrid backgrounds.
2. Brown midrib sorghum is associated with reduced pathogens. Lignin biosynthesis mutants, bmr6 or bmr12, were incorporated into sorghum grain lines to reduce lignin content and increase cell wall digestibility. Traditionally it was assumed that reduction in lignin biosynthesis would cause plants to be more susceptible to diseases. However, ARS researchers at Lincoln, NE showed that for infection by some Fusarium fungi, the mutant lines were actually more resistant. There was a significant reduction in grain infections of field grown plants and stalk infections of plants inoculated in the greenhouse. In particular, one Fusarium species, commonly-found in wild-type grain, was not detected in bmr12 grain. This research provides evidence that sorghum modified for increased bioenergy use could also be more resistant to some pathogens.Sattler, S.E., Funnell-Harris, D.L., Pedersen, J.F. 2010. Efficacy of Singular and Stacked Brown Midrib 6 and 12 in Modification of Lignocellulose and Grain Chemistry. Journal of Agricultural and Food Chemistry. 58:3611-3616.