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Hybridity has a greater effect than paternal genome dosage on heterosis in sugar beet (Beta vulgaris) - PubMed

  • ️Mon Jan 01 2018

Hybridity has a greater effect than paternal genome dosage on heterosis in sugar beet (Beta vulgaris)

Brendan F Hallahan et al. BMC Plant Biol. 2018.

Abstract

Background: The phenomenon of heterosis is critical to plant breeding and agricultural productivity. Heterosis occurs when F1 hybrid offspring display quantitative improvements in traits to levels that do not occur in the parents. Increasing the genome dosage (i.e. ploidy level) of F1 offspring can contribute to heterosis effects. Sugar beet (Beta vulgaris) provides a model for investigating the relative effects of genetic hybridity and genome dosage on heterosis. Sugar beet lines of different ploidy levels were crossed to generate diploid and triploid F1 offspring to investigate the effect of; (1) paternal genome dosage increase on F1 heterosis, and; (2) homozygous versus heterozygous tetraploid male parents on F1 triploid heterosis. A range of traits of agronomic and commercial importance were analyzed for the extent of heterosis effects observed in the F1 offspring.

Results: Comparisons of parental lines to diploid (EA, EB) and triploid (EAA, EBB) F1 hybrids for total yield, root yield, and sugar yield indicated that there was no effect of paternal genome dosage increases on heterosis levels, indicating that hybridity is the main contributor to the heterosis levels observed. For all traits measured (apart from seed viability), F1 triploid hybrids derived from heterozygous tetraploid male parents displayed equivalent levels of heterosis as F1 triploid hybrids generated with homozygous tetraploid male parents, suggesting that heterosis gains in F1 triploids do not arise by simply increasing the extent of multi-locus heterozygosity in sugar beet F1 offspring.

Conclusions: Overall, our study indicates that; (1) increasing the paternal genome dosage does not enhance heterosis in F1 hybrids, and; (2) increasing multi-locus heterozygosity using highly heterozygous paternal genomes to generate F1 triploid hybrids does not enhance heterosis. Our findings have implications for the design of future F1 hybrid improvement programs for sugar beet.

Keywords: F1 hybrid; Genome dosage; Heterosis; Hybrid vigor; Hybridity; Polyploidy; Triploid.

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Figures

Fig. 1
Fig. 1

Cross-section of sugar beet fruits revealing seed inside. Representative F1 2× hybrid (EA) and its parent lines. Seed tissue is labelled A perisperm, and, B embryo. Red line is scale of 0.5 mm

Fig. 2
Fig. 2

Sugar beet seed characteristics of diploid and triploid F1 hybrids and their parent lines. Data are mean of four replicates (± SD). a Seed viability, b seed size, c embryo size, d perisperm size. Different genotypes specified in parentheses. DH = double haploid. * Best parent heterosis (P ≤ 0.05), † Mid-parent heterosis (P ≤ 0.05), NS Not significantly different (P > 0.05)

Fig. 3
Fig. 3

Agronomic and root quality traits of diploid and triploid F1 hybrids of sugar beet and their parental lines. Data are mean of four replicates (± SD). a Total yield, b root yield, c corrected sugar content, d corrected sugar yield. Different genotypes specified in parentheses. DH = double haploid. * Best parent heterosis (P ≤ 0.05), † Mid-parent heterosis (P ≤ 0.05), NS Not significantly different (P > 0.05)

Fig. 4
Fig. 4

Mean genome-wide heterozygosity rate of F1 3× hybrids of sugar beet generated in this experiment. Heterozygosity rate is calculated by the ratio of heterozygous SNPs to the total number of genome bases. Data are mean of three replicates (± SD). F1 3× hybrids with heterozygous male parents, F1 3× hybrid (FCC) and (GDD), are significantly more heterozygous than F1 3× hybrids with homozygous male parents, F1 3× hybrid (EAA) and (EBB). Statistical differences were determined with a one-way ANOVA and Tukey’s HSD test. Means assigned different letters are statistically different (P <  0.05)

Fig. 5
Fig. 5

Sugar beet fruit and seed characteristics of F1 triploid hybrids and their parent lines. Data are mean of four replicates (± SD). a Seed viability, b seed size, c embryo size, d perisperm size. Different genotypes specified in parentheses. * Best parent heterosis (P ≤ 0.05), † Mid-parent heterosis (P ≤ 0.05), NS Not significantly different (P > 0.05),

‡

Below mid-parent value (P ≤ 0.05)

Fig. 6
Fig. 6

Agronomic and root quality traits of F1 triploid hybrids of sugar beet and their parental lines. Data are mean of four replicates (± SD). a Total yield, b root yield, c corrected sugar content, d corrected sugar yield. Different genotypes specified in parentheses. * Best parent heterosis (P ≤ 0.05), † Mid-parent heterosis (P ≤ 0.05), NS Not significantly different (P > 0.05)

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