A Library Of Dosage Variants As a Fast Source Of Novel Populus Germplasm

Among the poplar clones with the highest biomass yields are hybrids, created through hybridization between species. Some of the best performing commercial F1 hybrids can be triploid (3x = 63) or, potentially, aneuploid (individuals with unbalanced chromosome sets), and can have transgressive phenotypes desirable for biomass production. Superior genotypes can thus result from interactions among genomic regions that are in different dosage. Unfortunately the chromosomal composition and genetic features of most commercial germplasms are poorly characterized and the potential of dosage variation is not yet fully integrated in breeding programs. We are using next generation sequencing-based genotyping and karyotyping to understand the consequences of dosage variation in Populus. Through sampling of commercial and wild populations, we have successfully identified both triploid and aneuploid individuals. To produce karyotype variants on a larger scale, we performed γ−irradiation of pollen to induce chromosomal breaks. We have recovered many individuals carrying either deletions or additional copies of chromosomal fragments of varying sizes. Similarly, interploidy crosses between diploid and triploid parents were used to produce a swarm of aneuploid individuals, in which whole chromosomes vary in dosage compared to their diploid siblings. We are characterizing these populations, with the goal of describing a library of dosage variants across all 19 chromosomes of the poplar genome. This library will allow us to explore correlations between chromosomal segments, their dosage and phenotypes, to identify commercially-relevant genomic combinations and integrate them in breeding programs.