Mineral Nutrients and Primary Metabolites Involved in Yellowing of Switchgrass During Early Regrowth.

Yellowing of plants significantly reduces the photosynthetic activity and may have prominent effect on subsequent growth and yield. This condition was observed in switchgrass plants during early regrowth in two sibling genotypes derived from the switchgrass accession (BN-13645-64), acquired from GRIN by the Noble Foundation at Ardmore, Oklahoma. Near infrared spectrophotometry (NIR) for elemental analysis, and gas chromatography/mass spectrophotmetry (GC/MS) for primary metabolite analysis were employed. The non-yellowed genotype in one of the four biological replications was kept as the control.  The same plants showed the yellowing phenotype in two consecutive years at the Research Park, Ardmore, Oklahoma. All the yellow plants regain greenness at later developmental stages. NIR results indicated increased levels of calcium, phosphorous, and potassium in the yellowed genotypes when compared to the control. Marked levels of increase in Magnesium (41%), Ash (30%), Crude Protein (10%), and In Vitro True Digestibility (2%) in the yellowed plants compared to the control. GC/MS analysis on the eight samples yielded a total of 493 components and 263 targets. Maltose, raffinose, and galactinol showed marked increase in the green control plant than the yellowed plants. Acids of the Tricarboxylic Acid Cycle (TCA) like oxalic acid, succinic acid, fumaric acid, and several other disaccharides were higher in yellow plants than in the green plant. Further experiments are currently underway to investigate the significance of these preliminary findings.