Heritability of Cell Wall Carbohydrates in Switchgrass

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Abstract
Cell wall monosaccharides are closely associated with forage digestibility in switchgrass (Panicum virgatum L.). This study was conducted to estimate the feasibility of using these monomers as selection criteria to increase in vitro dry matter disappearance (IVDMD) of switchgrass. Thirty‐three parents were selected from a population of 660 plants on the basis of forage yield, IVDMD and N concentration. The 33 parents and their half‐sib progeny were evaluated during 1985 and 1986, at Clayton, NC, in separate fields with four replicates per field. First and second harvest plant samples of the parents and their offspring were assayed for IVDMD, acid detergent fiber (ADF), neutral detergent fiber (NDF), concentrations of arabinose (ARA), galactose (GAL), glucose (GLU) and (XYL), and ratios of the monosaccharides. Narrow‐sense heritability was estimated on a family mean basis and from parent‐offspring covariances. Broad‐sense heritability was estimated from parent variance components. A relatively low family mean heritability estimate was obtained for ARA, while GAL, GLU, and XYL were moderately heritable. Only initial growth XYL in the parents and regrowth XYL in progeny significantly interacted with years. The genotypic correlation between GLU and IVDMD in regrowth was positive (rG= 0.81) and exceeded three times its standard error, while the genotypic correlation between IVDMD and XYL (rG = −0.91) was significantly negative. The digestible cell wall (DCW) fraction of NDF residues was significantly positively correlated with GLU (rG = −0.92) in regrowth and significantly negatively correlated with XYL (rG = −0.81) in initial growth. Monomeric ratios of ARA:GLU, GAL:GLU, and XYL:GLU were highly negatively correlated with IVDMD and DCW and positively correlated with ADF and NDF. Based on predicted gains from selection, correlated responses of IVDMD are expected to be greatest when using clonal selection or modified earto‐row selection for reductions in the ARA:GLU or XYL:GLU ratios.
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