Robert J. Saville, Tom Passey, Judit Linka, Karen Russell and Richard J. Harrison
Genetics and Crop Improvement, East Malling Research
As part of the Nornex consortium EMR has been screening a collection of UK ash clones collected as part of historic DEFRA projects and by members of the Future Trees Trust. A partial analysis of the diversity of UK ash has previously been reported (Sutherland et al. 2010). Throughout the year, trees were evaluated for floral sexual morphology, leaf emergence, senescence and presence of potential Hymenoscyphus pseudoalbidus infection. The ultimate aim of this work is to identify putative resistant trees and ascertain whether previously reported correlations between senescence date and disease tolerance could be observed in UK ash material (Kjaer et al. 2012; McKinney et al. 2011; McKinney et al. 2012).
Ash populations, described in the downloadable spreadsheet are in the most part duplicate populations, planted in two phases in 2008-2009.
Methods and Results
Tree sex was determined using the trait descriptors shown in Figure 1 (below). Data is presented in the supplementary excel file, in the tab labeled Tree Sex. These data are valuable for future breeding and selection of both males and females that display resistance.
Figure 1. Flower types observed on ash (Fraxinus excelsior L.). a) male flower (prior to anthesis), b) hermaphrodite flower with rudimentary gynoecium (functionally male), c) hermaphrodite flower, d) hermaphrodite flower with vestigial anthers (functionally female) and, e) female flower.
Leaf emergence was scored based on the trait descriptors shown in Figure 2 (below). Data is presented in the supplementary excel file, in the tab labeled Leaf Emergence. These data may be useful when identifying traits correlated with local niche (i.e. altitude/ latitude), which may be important for the successful introduction of resistant material in future.
Senescence was recorded using three different descriptors (listed in Table 1-3). These traits were leaf loss, leaf colour and rachis retention, all of which may be significantly related to disease escape. These data are presented in the supplementary excel file, in the tab labeled Senescence.
Table 1: Trait descriptor for leaf loss
|Leaf Loss Trait||Description|
|1||no leaf loss|
|2||1-25% leaf loss|
|3||26-50% leaf loss|
|4||51-75% leaf loss|
|5||76-99%% leaf loss|
|6||100% leaf loss|
Table 2: Trait descriptor for leaf colour scale (adapted from McKinney et al. 2011)
|Leaf Colour Trait||Description|
|1||dark green leaves|
|2||~25% yellow leaves|
|3||~50% yellow leaves|
|4||~75% yellow leaves|
|5||completely yellow and fading leaves|
|6||necrosis (brown leaves)|
Table 3: Trait descriptor for rachis retention (to assess disease escape significance)
|Rachis retention scale||Description|
|Y||rachis detach easily when pulled through hand|
|N||rachis do not detach when pulled through hand|
Disease was recorded throughout the season in 2013, at which point (barring a single pre-existing lesion) no symptoms of foliar disease were observed during the growing season. However, in early 2014 disease assessment of dormant trees revealed several accessions with lesions on first year wood (i.e. infection that occurred during 2013) but was not observed from assessments. These results are presented in the Disease tab of the supplementary excel file, as are full diary records of dates of recording in the season diary tab. Subsequent isolation from the leading edge of suspect lesions confirmed the presence of cultures consistent with H. pseudoalbidus. PCR validation is underway, though all hallmarks of both lesions and subsequent cultures and indicative of H. pseudoalbidus being present.
Link to raw data at OADB github supplementary excel file
Kjaer, E.D. et al., 2012. Adaptive potential of ash (Fraxinus excelsior) populations against the novel emerging pathogen Hymenoscyphus pseudoalbidus. Evolutionary Applications, 5(3), pp.219–228.
McKinney, L. V et al., 2011. Presence of natural genetic resistance in Fraxinus excelsior (Oleraceae) to Chalara fraxinea (Ascomycota): an emerging infectious disease. Heredity, 106(5), pp.788–97.
McKinney, L. V. et al., 2012. Genetic resistance to Hymenoscyphus pseudoalbidus limits fungal growth and symptom occurrence in Fraxinus excelsior. Forest Pathology, 42(1), pp.69–74.
Sutherland, B.G. et al., 2010. Molecular biodiversity and population structure in common ash (Fraxinus excelsior L.) in Britain: implications for conservation. Molecular ecology, 19(11), pp.2196–211.