The possible drivers and implications of an observed latitudinal cline in disease resistance of a host tree were examined. Mycosphaerella leaf disease (MLD) damage, caused by Teratosphaeria species, was assessed in five Eucalyptus globulus (Tasmanian blue gum) common garden trials containing open-pollinated progeny from 13 native-forest populations. Significant population and family within population variation in MLD resistance was detected, which was relatively stable across different combinations of trial sites, ages, seasons and epidemics. A distinct genetic-based latitudinal cline in MLD damage among host populations was evident. Two lines of evidence argue that the observed genetic-based latitudinal trend was the result of direct pathogen-imposed selection for MLD resistance. First, MLD damage was positively associated with temperature and negatively associated with a prediction of disease risk in the native environment of these populations; and, second, the quantitative inbreeding coefficient (Q ST ) significantly exceeded neutral marker F ST at the trial that exhibited the greatest MLD damage, suggesting that diversifying selection contributed to differentiation in MLD resistance among populations. This study highlights the potential for spatial variation in pathogen risk to drive adaptive differentiation across the geographic range of a foundation host tree species.

Harnessing the biotechnological potential of the large number of proteins available in sequence databases requires scalable methods for functional characterization. Here we propose a workflow to address this challenge by combining phylogenomic guided DNA synthesis with high-throughput mass spectrometry and apply it to the systematic characterization of GH1 β-glucosidases, a family of enzymes necessary for biomass hydrolysis, an important step in the conversion of lignocellulosic feedstocks to fuels and chemicals. We synthesized and expressed 175 GH1s, selected from over 2000 candidate sequences to cover maximum sequence diversity. These enzymes were functionally characterized over a range of temperatures and pHs using nanostructure-initiator mass spectrometry (NIMS), generating over 10,000 data points. When combined with HPLC-based sugar profiling, we observed GH1 enzymes active over a broad temperature range and toward many different β-linked disaccharides. For some GH1s we also observed activity toward laminarin, a more complex oligosaccharide present as a major component of macroalgae. An area of particular interest was the identification of GH1 enzymes compatible with the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), a next-generation biomass pretreatment technology. We thus searched for GH1 enzymes active at 70 °C and 20% (v/v) [C2mim][OAc] over the course of a 24-h saccharification reaction. Using our unbiased approach, we identified multiple enzymes of different phylogentic origin with such activities. Our approach of characterizing sequence diversity through targeted gene synthesis coupled to high-throughput screening technologies is a broadly applicable paradigm for a wide range of biological problems.

A trial was undertaken to assess the extent to which variation in sawn-board quality traits of plantationgrown Eucalyptus nitens is under genetic control and amenable to genetic improvement. Five hundred and sixty trees from 129 families and three central Victorian races were sampled from an open-pollinated progeny trial in Tasmania, Australia. Acoustic wave velocity (AWV) was assessed on standing trees and sawlogs. Wedges from disks extracted from sawlogs were assessed for basic density and checking. Processed boards from 496 of the trees were assessed for board stiffness (static modulus of elasticity, MOE), and internal and surface checking. Genetic differences among races were significant for AWV and MOE traits. The Southern race had the highest mean values for these traits. Significant additive genetic variation within races was observed in all traits, demonstrating that the quality of plantation-grown E. nitens boards could be improved through breeding. Estimated narrow-sense heritabilities were 0.85 for standing-tree AWV, 0.71 for log AWV, 0.37 for board MOE, and ranged from 0.20 to 0.52 for checking traits. A strongly positive genetic correlation (r g =1.05) was observed between standing-tree AWV and board MOE, indicating that AWV could be used as a selection trait to improve E. nitens board stiffness. The genetic correlation between basic density and board MOE was also positive (r g =0.62). However, a significant and adverse genetic correlation (r g =0.61) was identified between basic density and surface check length. Wood stiffness and checking traits were more-or-less genetically independent, and genetic correlations between surface and internal checking were positive but only moderate (r g =0.48-0.52).

Eucalyptus nitens plantations are generally established for pulpwood production but an increasing area is being managed for solid wood. Genetic variation in, and correlations among, three Kraft pulpwood traits (diameter at breast height, basic density and near-infrared-predicted cellulose content) and three 12-mm wood-core shrinkage traits (recoverable collapse, net shrinkage and gross shrinkage) were examined, utilising data from two 9-year-old firstgeneration progeny trials in Tasmania. These trials contained approximately 400 open-pollinated families (over 100 of which were sampled for wood properties) representing three central-Victorian E. nitens races. Significant genetic variation at the race and/or within-race level was identified in all traits. Within races, relative levels of additive genetic variation were higher for shrinkage traits, although narrowsense heritabilities were lower and the expression of genetic variation less stable across sites than for other wood property traits. Heterogeneous intertrait genetic correlations were identified across sites between growth and some wood property traits. However, where significant, genetic correlations indicated that within-race selection for growth would adversely affect core basic density and all core shrinkage traits. Furthermore, results based on cores suggested that within-race selection for higher basic density would favourably impact on cellulose content and collapse but selection for either higher basic density or cellulose content would adversely affect net shrinkage. Most within-race genetic variation in gross shrinkage appeared to be due to genetic variation in collapse. The implications of these results for sawn timber breeding will depend on the strength of genetic correlations between core traits and rotation-age objective traits and objective trait economic weights.