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Title:   Author  item
                                            Gleason, Sean
  Submitted to: American Society of Agronomy Meetings
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 6/15/2015
                                    Publication  Date: 6/15/2015
                                    Citation: Gleason, S.M. 2015. Why aren’t more plant breeders and geneticists interested in xylem traits?. American Society of Agronomy Meetings. Synergy in Science. 264:2.Interpretive Summary:
                                Technical Abstract: Plants in all habitats need to maintain an adequate supply of water to the sites of photosynthesis and evaporation within their leaves. Although the efficiency and safety (i.e., safe from embolism) of this water supply have been long appreciated, the importance of these traits in conferring fitness across the world’s angiosperm species are now coming to light, mainly through the connectivity of large datasets. However, despite evident relationships between xylem traits and aridity, few breeding and transgenic studies have focused on xylem traits. Here, we present our present knowledge of xylem-climate relationships. We then ask, on the basis of these relationships, which traits are likely to confer drought resistance in crop plants?  

Climate explained meaningful proportions of variation in xylem traits across the globe. In arid habitats, natural selection has favored strategies that increase the embolism resistance of xylem, investment in xylem tissue per unit leaf area, as well as the density of xylem tissue. Mean annual precipitation and soil water potential explained 11 – 19% and 14 – 54% of the variation in hydraulic traits across a global spread of species. Long-assumed tradeoffs between xylem efficiency and xylem safety, as well as the often assumed tradeoff between xylem efficiency and mechanical safety were not supported by the analysis.    

Soil water potential was positively correlated with the efficiency of xylem tissue to transport water (r2 = 0.25; n = 261) and negatively correlated with xylem safety; the capacity of xylem to resist embolism (r2 = 32; n = 139). However, these two traits did not tradeoff against one another (r2 = 0.062; n = 274), suggesting that modern breeding techniques could provide independent selection of each, providing sufficient hereditable variation. The analysis also suggests that selection for more conductive sapwood is not likely result in weaker xylem or less safe plant stems, as is often assumed. 

The evolutionary alignment between aridity and xylem traits suggests that xylem transformation was key to angiosperm success in arid habitats. As such, it is likely that these same traits could confer drought resistance in crop species. We suggest that research directed towards finding the genes coding for these traits, as well as their posttranscriptional regulation should be a research priorities for agriculture.


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