Abstract
Crop wild relatives (CWR) are a rich source of genetic diversity for crop improvement. Combining ecogeographic and phylogenetic techniques can inform both conservation and breeding. Geographic occurrence, bioclimatic, and biophysical data were used to predict species distributions, range overlap and niche occupancy in 36 taxa closely related to sunflower (Helianthus annuus L.). Taxa lacking comprehensive ex situ conservation were identified. The predicted distributions for 36 Helianthus taxa identified substantial range overlap, range asymmetry and niche conservatism. Specific taxa (e.g., Helianthus deblis Nutt., Helianthus anomalus Blake, and Helianthus divaricatus L.) were identified as targets for traits of interest, particularly for abiotic stress tolerance, and adaptation to extreme soil properties. The combination of techniques demonstrates the potential for publicly available ecogeographic and phylogenetic data to facilitate the identification of possible sources of abiotic stress traits for plant breeding programs. Much of the primary genepool (wild H. annuus) occurs in extreme environments indicating that introgression of targeted traits may be relatively straightforward. Sister taxa in Helianthus have greater range overlap than more distantly related taxa within the genus. This adds to a growing body of literature suggesting that in plants (unlike some animal groups), geographic isolation may not be necessary for speciation.
Highlights
Plant genetic resources represent the biological foundation for maintaining and improving crop productivity having played a central role in crop development from antiquity (Porter et al, 2014)
(1) target taxa were identified, and geographic occurrence data were gathered and verified, (2) the overall representation of Crop wild relatives (CWR) in germplasm collections was estimated, (3) potential distribution models were produced for taxa with sufficient samples with coordinates, (4) the geographic and ecological representation of germplasm collections were assessed for each taxon by comparing potential distribution models to existing germplasm collection locations, (5) taxa were prioritized for further collecting based upon the average of their overall, geographic, and ecological coverage results, and (6) gap analysis results were correlated with the subjective assessments of collection priorities from crop experts
Ecogeographic variables for cultivated sunflower were extracted from the area of species distribution maps (Monfreda et al, 2008) at a resolution of 5 arc-min, with a random sample of 1000 points weighted by harvested area taken from major production regions
Summary
Plant genetic resources represent the biological foundation for maintaining and improving crop productivity having played a central role in crop development from antiquity (Porter et al, 2014). CWR have traditionally been categorized based on crossing relationships with domesticates; the primary germplasm contains no crossing barriers, the secondary contains some meiotic abnormalities, and the tertiary requires special techniques such as embryo rescue (Harlan and de Wet, 1971; Harlan, 1976). Such classifications may be supplemented by molecular, bioclimatic, and biophysical data to aid in the identification of candidate taxa for breeding, such efforts have been constrained by challenges in comprehensively generating and integrating these data (Ricklefs and Jenkins, 2011)
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