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Design of an F1 hybrid breeding strategy for ryegrasses based on selection of self-incompatibility locus-specific alleles.

Pembleton LW, Shinozuka H, Wang J, Spangenberg GC, Forster JW, Cogan NO - Front Plant Sci (2015)

Bottom Line: This property is partially due to an inability to effectively exploit heterosis through the formation of F1 hybrids.Based on simulation of various levels of SI allele diversity restriction, the most effective scheme will generate 83.33% F1 hybrids.Results from the study, including the impact of varying flowering time, are discussed along with a proposed breeding design for commercial application.

View Article: PubMed Central - PubMed

Affiliation: Biosciences Research Division, AgriBio, La Trobe University Bundoora, VIC, Australia ; Dairy Futures Cooperative Research Centre, AgriBio, La Trobe University Bundoora, VIC, Australia ; School of Applied Systems Biology, La Trobe University Bundoora, VIC, Australia.

ABSTRACT
Relatively modest levels of genetic gain have been achieved in conventional ryegrass breeding when compared to cereal crops such as maize, current estimates indicating an annual improvement of 0.25-0.6% in dry matter production. This property is partially due to an inability to effectively exploit heterosis through the formation of F1 hybrids. Controlled crossing of ryegrass lines from geographically distant origins has demonstrated the occurrence of heterosis, which can result in increases of dry matter production in the order of 25%. Although capture of hybrid vigor offers obvious advantages for ryegrass cultivar production, to date there have been no effective and commercially suitable methods for obtaining high proportions of F1 hybrid seed. Continued advances in fine-scale genetic and physical mapping of the gametophytic self-incompatibility (SI) loci (S and Z) of ryegrasses are likely in the near future to permit the identification of closely linked genetic markers that define locus-specific haplotypes, allowing prediction of allelic variants and hence compatibility between different plant genotypes. Given the availability of such information, a strategy for efficient generation of ryegrass cultivars with a high proportion of F1 hybrid individuals has been simulated, which is suitable for commercial implementation. Through development of two parental pools with restricted diversity at the SI loci, relative crossing compatibility between pools is increased. Based on simulation of various levels of SI allele diversity restriction, the most effective scheme will generate 83.33% F1 hybrids. Results from the study, including the impact of varying flowering time, are discussed along with a proposed breeding design for commercial application.

No MeSH data available.


Proportion of plants in each of the three genotype groups present in Se1, and the compatible (solid black lines) and incompatible (dashed red lines) pollen-specific SI alleles between each group.
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Figure 2: Proportion of plants in each of the three genotype groups present in Se1, and the compatible (solid black lines) and incompatible (dashed red lines) pollen-specific SI alleles between each group.

Mentions: Within Se1, the presence of only two alleles at S and Z and the mechanics of the SI process ensured that no individual will be homozygous at both S and Z, causing the genotypes to fall into three groups: those homozygous at one locus, those homozygous at the same locus but for the alternate allele, and those heterozygous at both the S and Z loci (Figure 2). A total of 50% of the individuals will belong to the fully heterozygous group, while the remaining individuals will be distributed between the other two groups, at 25% each. This simple 1:2:1 Mendelian ratio is maintained over each generation of crossing within the pool, such that only the identity of the homozygous locus alternates between generations (Supplemental Figure 1). The 1:2:1 ratio of genotypic groups was also found to be “self-correcting,” such that if the groups were not represented at this ratio during crossing, or if pollen-specific SI alleles were not distributed across the field in a 1:2:1 ratio, the generated progeny would still conform to expectation. The individuals in each generation that are heterozygous at both S and Z will not yield any seed, as none of the pollen-specific alleles from the other genotypes are unique (when compared to the genotype of the heterozygous plant) (Figure 2). Although only 66.67% of the pollen alleles are compatible with those of the other two groups, it is assumed that pollen availability is not limiting and that sufficient numbers of compatible alleles will be available for fertilization of these plants, leading to 100% seed production. For the seed multiplication phases within the parental pools of Se1, an overall seed production penalty of 50% is sustained within the pool (Table 2). For all of the other breeding schemes, due to the presence of more than two alleles at either S or Z, no individuals are ever heterozygous for all the alleles that are present within the parental pools, and so these schemes exhibited no seed production penalties during the simulation process (Table 2).


Design of an F1 hybrid breeding strategy for ryegrasses based on selection of self-incompatibility locus-specific alleles.

Pembleton LW, Shinozuka H, Wang J, Spangenberg GC, Forster JW, Cogan NO - Front Plant Sci (2015)

Proportion of plants in each of the three genotype groups present in Se1, and the compatible (solid black lines) and incompatible (dashed red lines) pollen-specific SI alleles between each group.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585157&req=5

Figure 2: Proportion of plants in each of the three genotype groups present in Se1, and the compatible (solid black lines) and incompatible (dashed red lines) pollen-specific SI alleles between each group.
Mentions: Within Se1, the presence of only two alleles at S and Z and the mechanics of the SI process ensured that no individual will be homozygous at both S and Z, causing the genotypes to fall into three groups: those homozygous at one locus, those homozygous at the same locus but for the alternate allele, and those heterozygous at both the S and Z loci (Figure 2). A total of 50% of the individuals will belong to the fully heterozygous group, while the remaining individuals will be distributed between the other two groups, at 25% each. This simple 1:2:1 Mendelian ratio is maintained over each generation of crossing within the pool, such that only the identity of the homozygous locus alternates between generations (Supplemental Figure 1). The 1:2:1 ratio of genotypic groups was also found to be “self-correcting,” such that if the groups were not represented at this ratio during crossing, or if pollen-specific SI alleles were not distributed across the field in a 1:2:1 ratio, the generated progeny would still conform to expectation. The individuals in each generation that are heterozygous at both S and Z will not yield any seed, as none of the pollen-specific alleles from the other genotypes are unique (when compared to the genotype of the heterozygous plant) (Figure 2). Although only 66.67% of the pollen alleles are compatible with those of the other two groups, it is assumed that pollen availability is not limiting and that sufficient numbers of compatible alleles will be available for fertilization of these plants, leading to 100% seed production. For the seed multiplication phases within the parental pools of Se1, an overall seed production penalty of 50% is sustained within the pool (Table 2). For all of the other breeding schemes, due to the presence of more than two alleles at either S or Z, no individuals are ever heterozygous for all the alleles that are present within the parental pools, and so these schemes exhibited no seed production penalties during the simulation process (Table 2).

Bottom Line: This property is partially due to an inability to effectively exploit heterosis through the formation of F1 hybrids.Based on simulation of various levels of SI allele diversity restriction, the most effective scheme will generate 83.33% F1 hybrids.Results from the study, including the impact of varying flowering time, are discussed along with a proposed breeding design for commercial application.

View Article: PubMed Central - PubMed

Affiliation: Biosciences Research Division, AgriBio, La Trobe University Bundoora, VIC, Australia ; Dairy Futures Cooperative Research Centre, AgriBio, La Trobe University Bundoora, VIC, Australia ; School of Applied Systems Biology, La Trobe University Bundoora, VIC, Australia.

ABSTRACT
Relatively modest levels of genetic gain have been achieved in conventional ryegrass breeding when compared to cereal crops such as maize, current estimates indicating an annual improvement of 0.25-0.6% in dry matter production. This property is partially due to an inability to effectively exploit heterosis through the formation of F1 hybrids. Controlled crossing of ryegrass lines from geographically distant origins has demonstrated the occurrence of heterosis, which can result in increases of dry matter production in the order of 25%. Although capture of hybrid vigor offers obvious advantages for ryegrass cultivar production, to date there have been no effective and commercially suitable methods for obtaining high proportions of F1 hybrid seed. Continued advances in fine-scale genetic and physical mapping of the gametophytic self-incompatibility (SI) loci (S and Z) of ryegrasses are likely in the near future to permit the identification of closely linked genetic markers that define locus-specific haplotypes, allowing prediction of allelic variants and hence compatibility between different plant genotypes. Given the availability of such information, a strategy for efficient generation of ryegrass cultivars with a high proportion of F1 hybrid individuals has been simulated, which is suitable for commercial implementation. Through development of two parental pools with restricted diversity at the SI loci, relative crossing compatibility between pools is increased. Based on simulation of various levels of SI allele diversity restriction, the most effective scheme will generate 83.33% F1 hybrids. Results from the study, including the impact of varying flowering time, are discussed along with a proposed breeding design for commercial application.

No MeSH data available.