Association genetics approach to identification of hybrids in pinus contorta - pinus banksiana complex

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Correct identification of natural hybrids between Pinus contorta Dougl. ex Loud. and P. banksiana Lamb. (PCBC) is essential for assessing their evolutionary significance. Despite numerous morphological, biochemical and molecular studies conducted over decades, hybrids identification from this hybrid zone remains difficult for two main reasons. First, classic Anderson's hybrid index or similar morphometric indices are based on marked phenotypic differences between hybrids and their parental species but the observed character correlation and morphological intermediacy could arise from evolutionary phenomena (e.g., remnants of ancestral population of two isolated species) other than hybridization per se. Second, a lack of unique molecular markers for parental genotypes and the close genetic affinity among PCBC populations have not significantly improved the capability of morphological characters to separate hybrids from the parental species. Recent advances in discovery of vast numbers of single nucleotide polymorphism (SNP) markers in many species including pines have raised prospects of genomewide association studies. However, due to the large genome sizes (~30 billion bp) and rapid decay of linkage disequilibrium (within 1000 bp or faster) in outcrossing pines, a candidate gene approach is more appropriate for these conifers. In this proposal, I will develop a 'quais-genomewide' hybrid index for drought tolerance from affordable and abundant SNPs towards unambiguous identification of hybrids and parental individuals and populations in PCBC complex. I will use total tree height as a surrogate to measure phenotypic variation among 36 PCBC populations in response to drought. The 'quasi-genomewide' hybrid index for drought tolerance will be then predicted as the sum of genotypic (breeding) values across all SNP markers under different mixed models. The proposed association genetics approach to identification of hybrids uses the latest mixed-model developments that allow for combining the information of adaptive traits with SNP markers and thus is a major step towards resolving a longstanding issue of classification and use of natural hybrids.