Genetic Analysis of Yield and Quality Traits in Switchgrass Based on Population Crosses

Serge Edmé,Rob Mitchell

doi:10.3390/agronomy11112220

Abstract

Obtaining greater genetic gains, particularly for biomass yield, requires a good understanding of the gene action governing the inheritance of traits with economic importance in switchgrass (Panicum virgatum L.). Individual genotypes from three different accessions were crossed in single-pair matings with reciprocals to assess the relative importance of additive to nonadditive genetic variation and the potential of using inter-ecotypic crosses to improve dry matter yield (DMY), in vitro dry matter digestibility (IVDMD), lignin content (ADL and KL), and ethanol yield (ETOH). Crosses and four reference populations were planted in a randomized complete block design with eight replications of single family-rows plots, with five-plants each and 1 m spacings. A linear mixed model was applied as per the restricted maximum likelihood method, integrated with a pedigree tracing back to the original founders of these parental populations, and augmented with the designation of four genetic groups. Variation due to SCA (specific combining ability) was predominant for all traits, contributing from 20% to 57% of the total phenotypic variation and with Baker’s ratios (GCA/SCA) varying from 0.003 to 0.67. Heritability values calculated at the fullsib-family mean level were moderate to very high. Variation due to GCA (general combining ability) was detected with a lesser significance for DMY and ETOH. A reciprocal GCA effect was present in the form of maternal inheritance for DMY, suggesting the use of the highest biomass-yielding parent as female in inter-ecotypic breeding. Selecting and deploying fullsib families, deploying clonal hybrids, and adopting an introgression breeding approach are all possibilities available to switchgrass breeders to exploit the complementary genes from this germplasm and capitalize on the non-additive genetic variation present in these crosses.

Highlights

Switchgrass (Panicum virgatum L.) is an economically and ecologically important crop species in the USA, providing forage for livestock, for prairie restoration, for landscaping, and potentially for biofuel production [1]
Biomass yield is one of the traits in switchgrass that breeders struggle to improve over time, with the reason being a combination of its negative genetic correlation with quality traits when breeding for forage and of more selection emphasis given to quality traits
The inheritance of the trait was never questioned with ample additive genetic variation reported in genetic studies [5,6]

Summary

Introduction

Switchgrass (Panicum virgatum L.) is an economically and ecologically important crop species in the USA, providing forage for livestock, for prairie restoration, for landscaping, and potentially for biofuel production [1]. The USDA-ARS breeding program in Lincoln NE released the first bioenergy cultivar as “Liberty” after one cycle of selection in an upland (“Summer”) × lowland (“Kanlow”) population [4]. Breeding switchgrass is ordinarily and primarily based on exploiting additive genetic variation in halfsib recurrent selection protocols within ecotypic populations adapted for a specific region of the country [5]. Parents are collected from wild stands in the prairies, tested, and selected for crossing in wind-pollinated nurseries. Seed is collected from the female tassels and tested as halfsib (open-pollinated) families. Selection is first practiced between and within families in the progeny tests to obtain parents of the generation. Deployment of seed of the new cultivar is produced by wind/mass pollination after at least three cycles of multiplication without selection

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