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Submitted to: Crop Science
Publication Type: Review Article Publication Acceptance Date: 1/3/2017 Publication Date: 3/16/2017 Publication URL: https://handle.nal.usda.gov/10113/5700670 Citation: Edme, S.J., Mitchell, R., Sarath, G. 2017. Genetic parameters and prediction of breeding values in switchgrass bred for bioenergy. Crop Science. 57:1-11. doi:10.2135/cropsci2016.09.0770. Interpretive Summary: There is an increasing interest in the world to convert plant feedstocks and residues into solid or liquid biofuels. Several research programs in the US are targeting switchgrass, an indigenous perennial grass, to increase its biomass yield and reduce its lignin content by breeding. This study evaluates the bioenergy potential of a breeding population of switchgrass, developed at USDA-ARS in Lincoln, NE by crossing two different (eco)types (Summer and Kanlow), after two successive generations. The results indicate that there is substantial variation in each generation for biomass yield, lignin, and ethanol yield in the population to improve its potential. However, breeding has brought some changes in the correlations (relationships) among the three traits. In the second generation, selecting for high biomass yield would meet the goal of simultaneously decreasing lignin content and increasing the ethanol yield of the plants. In the third generation, the same relationships between biomass yield and lignin or between lignin and ethanol yield existed, but the strengths were reduced by about half. The relationship between biomass yield and ethanol yield decreased from significant to zero. As these relationships weigh considerably in the selection of potential parents of each generation, the strategy adopted is to recurrently assess their genetic merit at transmitting genes that confer high biomass and ethanol yields and low lignin content. Technical Abstract: Estimating genetic parameters is an essential step in breeding by recurrent selection to maximize genetic gains over time. This study evaluated the effects of selection on genetic variation across two successive cycles (C1 and C2) of a ‘Summer’x‘Kanlow’ switchgrass (Panicum virgatum L.) population. Two progeny tests were planted in 2007 and 2011 near Mead, NE and respectively analyzed for 2 and 4 yr. Each test was a randomized complete block design, with four replicates of 34 halfsib families in single-row plots of 10 seedlings in C1 and with three replicates of 111 halfsib families in single-row plots of five seedlings in C2. The C2 test included C0, C1, and parental populations for comparison. Multivariate mixed linear models revealed ample additive genetic variation for dry matter yield (DMY), Klason lignin (KL), and predicted ethanol yield (ETOH) in both cycles, with heritability ranging from 0.40±0.18 to 0.5±0.14 at the family level, from 0.22±0.17 to 0.36±0.22 at the individual level, and from 0.25 to 0.31 within family in C1. Matching values in C2 were: from 0.42±0.09 to 0.63±0.07, from 0.10±0.07 to 0.34±0.13, and from 0.12 to 0.48. More opportunity exists to improve DMY, with a coefficient of additive genetic variation of 11 to 32%, than KL (3–5%) or ETOH (3–6%). The traits were properly aligned for joint improvement for high DMY and reduced KL in C1, owing to favorable genetic correlations (rA=-0.33±0.11) and each having respective rA of 0.60±0.05 and -0.62±0.07 with ETOH. In C2, the rA between DMY and KL (-0.19±0.10) or ETOH (0.04±0.04) decreased towards zero, and that between KL and ETOH was moderately less negative (-0.35±0.15). These results suggest a strong genetic basis for improvement of the traits and monitoring of their patterns every cycle to find the proper weights that maximize the breeding goal of designing the ideal bioenergy switchgrass. |
