Abstract
The efficient use of sorghum as a renewable energy source requires high biomass yields and reduced agricultural inputs. Hybridization of Sorghum bicolor with wild Sorghum halepense can help meet both requirements, generating high-yielding and environment friendly perennial sorghum cultivars. Selection efficiency, however, needs to be improved to exploit the genetic potential of the derived recombinant lines and remove weedy and other wild traits. In this work, we present the results from a Genome-Wide Association Study conducted on a diversity panel made up of S. bicolor and an advanced population derived from S. bicolor × S. halepense multi-parent crosses. The objective was to identify genetic loci controlling biomass yield and biomass-relevant traits for breeding purposes. Plants were phenotyped during four consecutive years for dry biomass yield, dry mass fraction of fresh material, plant height and plant maturity. A genotyping-by-sequencing approach was implemented to obtain 92,383 high quality SNP markers used in this work. Significant marker-trait associations were uncovered across eight of the ten sorghum chromosomes, with two main hotspots near the end of chromosomes 7 and 9, in proximity of dwarfing genes Dw1 and Dw3. No significant marker was found on chromosomes 2 and 4. A large number of significant marker loci associated with biomass yield and biomass-relevant traits showed minor effects on respective plant characteristics, with the exception of seven loci on chromosomes 3, 8, and 9 that explained 5.2–7.8% of phenotypic variability in dry mass yield, dry mass fraction of fresh material, and maturity, and a major effect (R2 = 16.2%) locus on chromosome 1 for dry mass fraction of fresh material which co-localized with a zinc-finger homeodomain protein possibly involved in the expression of the D (Dry stalk) locus. These markers and marker haplotypes identified in this work are expected to boost marker-assisted selection in sorghum breeding.
Highlights
Sorghum [Sorghum bicolor (L.) Moench] is the fifth cereal in the world in terms of production and acreage (Ordonio et al, 2016a)
No significant differences were registered among the two groups for dry mass fraction of fresh materials (DMC: 37.4 vs. 36.8%, p = 0.28) and yield (DMY: 20.2 vs. 18.8 t/ha, p = 0.11)
Our data suggest that hybridization of domesticated sorghum with S. halepense can be useful for enhancing biomass production, especially if negative traits transmitted by the wild parent, such as seed chattering will be eliminated by breeding techniques including crossing and/or backcrossing to S. bicolor followed by selection
Summary
Sorghum [Sorghum bicolor (L.) Moench] is the fifth cereal in the world in terms of production and acreage (Ordonio et al, 2016a). The S. bicolor genome sequence was first released in 2009 (Paterson et al, 2009) and the current version is 3.1.1; it is sized 732.2 Megabases (Mb), arranged in x = 10 (2n = 20) chromosomes and reporting more than 34,000 annotated genes several of which can be harnessed in genetic introgressions to improve biomass production in this crop (McCormick et al, 2018). Perennial crops are considered a paradigm shift in modern farming owing to their potential to help the world move toward more sustainable production and environment friendlier systems to increase food security while reducing tillage, water consumption, soil erosion and CO2 emissions (FAO, 2013). Cultivated sorghum could benefit from perenniality in terms of food, fodder and energy security, and in terms of sustainability, cutting environmental load through increased energy balance, and soil protection (Hallam et al, 2001)
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