Breeding for cell wall characteristics linked to improved saccharification efficiency in alfalfa

Bertrand, A., Claessens, A., Thivierge, M.-N., and Rocher, S. 2017. Breeding for cell wall characteristics linked to improved saccharification efficiency in alfalfa. Plant Biology 2017, Honolulu, June 24-28 2017.

Abstract

Alfalfa (Medicago sativa L.) is an open-pollinated autotetraploid species with extensive genetic variability for cell wall (CW) degradability that can be exploited for genetic improvement. However, genetic gains for this trait are tributary to the availability of screening techniques for the precise identification of superior genotypes. We developed a screening approach using glucose released from CW following enzymatic hydrolysis and Near Infra-Red Spectroscopy predictions. Using this approach, we identified genotypes that are more prone to enzymatic degradation and thus having higher saccharification potential. Here, the objective was to evaluate the effect of recurrent selection on enzyme-released glucose in alfalfa, and to evaluate the stability of that trait under field conditions. Alfalfa genotypes from two genetic backgrounds (cultivars 54V54 and Orca) were subjected to two cycles of phenotypic selection based on their CW enzyme-released glucose (G) concentrations. After each cycle, the genotypes with lowest (G-) and highest (G+) released glucose within each background were selected and intercrossed. Eight populations were generated and evaluated at three sites in Canada in 2014 and 2015. A significant response to selection was observed in both backgrounds, with the G+ populations having a significantly higher concentration of enzyme-released glucose at all experimental sites. For instance, the 54V54 G+2 population obtained after two cycles of positive recurrent selection had a CW concentration of enzyme-released glucose of 176 mg g-1 CW, 16% higher than initial population 54V54 (152 mg g-1 CW). After two years, field selection for that trait had no significant impact on alfalfa yield. Several SRAP polymorphisms varying in intensity between populations were identified and used to identify genes displaying allele frequency shifts in response to divergent selection for cell wall degradability. Phenotypic selection based on stem G concentrations is a very promising approach to improve alfalfa stem cell wall degradability without reducing plant biomass.

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