A single tree was selected a few metres away from the pocket of ash with extensive and severe symptoms of ash dieback at site 3. It had several well developed cankers at the base of the main stem which extended up to 1. The extent of callusing around the canker margins suggested that the cankers had been initiated some years earlier.
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The tree was felled in January and approximately 1 m of the cankered stem returned to the laboratory for analysis and dating. Prior to dating of the cankers, isolation of H. Isolates obtained were confirmed as H. An isolated room with no history of H. Prior to this, and to avoid any possibility of contamination with H. All the stem sections were also rinsed with 70 per cent ethanol for 1 min, followed by bleach solution for 1 min, and finished by a wash in sterile distilled water for 1 min, after which they were air-dried at room temperature. A mallet and chisel wiped with bleach and flame dried were used to split logs longitudinally, and a sliver of underlying xylem tissue beneath the canker was excised using a similarly cleaned scalpel.
All 29 DNA samples 27 from symptomatic material, 2 healthy controls were tested for the presence of H. Data analysis used the LightCycler version 1. Owner records provided planting year and details of the supplying nursery; the latter confirmed these records and the age of stock supplied Tables 1 and 2. The supplying nursery was in England but was known to occasionally supplement stock by purchasing trees from a wholesaler which routinely imported tree stock from mainland Europe.
Planting positions were clearly visible in aerial photographs. Initial investigation revealed one area of the stand with notably poorer growth. There was little mortality and the two trees that died in ca. Ash dieback symptoms were most developed in the area of poorest growth and some naturally regenerating ash trees in this area also had limited symptoms, indicating recent infection. All trees were established in tree shelters so no assessment for basal lesions was made. Apothecia were found readily under the symptomatic trees with poorer growth and less frequently elsewhere.
Occasional shoot dieback was observed on some mature trees immediately adjacent to the planted stand suggesting recent disease spread. No symptoms were identified in the many hedgerow trees dividing fields to the east of the site, and no infection was detected on younger recently planted ash stands m to the north. The 28 ha site comprised pure blocks of various broadleaf species originally planted in , with additional planting in ; planting year and plant origins were provided by the owner Tables 1 and 2.
Initial inspection suggested that a high percentage of the more recently -planted ash had symptoms consistent with H. Basal lesions were also common on trees in the same block but seen only infrequently in adjoining areas of ash. Overall, mortality was low and estimated year of death was between and Table 1. Symptoms were also occasionally identified in neighbouring mature ash woodlands. Another isolated site but with more recent signs of infection was found over 4.
This 27 ha broadleaf plantation planted from to contained older stands of ash planted in small groups, and younger plantings of ash in blocks of varying size. Symptoms on this site had been reported to be worst on trees planted in However, closer inspection revealed that although some trees planted several years earlier had only recently become infected, there were other pockets of similarly aged ash with severe symptoms, including a small number of trees with basal lesions suggesting a longstanding disease presence.
The most extensive dieback was concentrated in a group of approximately 20 ash trees, planted within a compartment of mixed broadleaved trees and adjacent to heavily affected areas of planted ash which were downhill. Mortality in this pocket was confined to seven trees which appeared to have died between and Table 1.
A further three trees sampled during a later visit were found to have died between and Table 2. Sporadic ash planted over a similar timescale were found with H. Most of the symptomatic trees were located to the east of the site, following the direction of prevailing winds. This extensive newly established 90 ha broadleaf wood was created between and on farmland which surrounded small pockets of long established ash woodland. The owner was able to confirm the planting years of compartments from site records. The supplying nursery was no longer in business, but anecdotal information suggested that it occasionally purchased stock from various sources including from mainland Europe.
Established trees were clearly visible in aerial photographs; the ash had generally been planted in small pure blocks. The amount of dieback across the site varied, but basal lesions were only occasionally observed. Although investigations initially concentrated on areas identified by Forestry Commission England aerial surveillance as those with the greatest levels of dieback, there was no single area where symptoms were more developed and therefore where the disease might have been present longer than elsewhere.
Only a single dead tree with typical ash dieback symptoms was identified Table 1. Apothecia were found readily on rachises across the large site, including under the mature canopy of one small ancient ash stand where they sometimes occurred on small woody material in the leaf litter rather than on rachises. However, other nearby sites were visited and confirmed to be infected as part of this in depth investigation. One dead tree was identified that had died between and Table 2. This small 3 ha site was planted in , and was originally owned, established from the same stock and managed by the same estate as site 6.
The two sites are approximately m apart, separated by a disused railway, open farmland and fragments of woodland, including older ash stands and younger, more recently planted ash. The owner was able to supply details of planting year and the supplying nursery. The latter also confirmed the age of stock supplied Tables 1 and 2 and confirmed that any Fraxinus stock supplied would have been grown on the nursery from seed.
Planting positions were clearly visible in the aerial photographs.
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Aerial surveillance of sites 5 and 6 revealed worse levels of dieback than elsewhere in the area, and the extent of dieback suggested a high level of mortality. However, ground inspection revealed most trees were still alive. Dead trees were scattered across the site, and some larger individuals appeared to have been entirely girdled by H.
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Apothecia and sclerotized rachises were also abundant across the site. Most of the dead trees were between 1 and 3 m in height, and initially 10 of the smallest dead trees with obvious cankers were dated as having died between and Table 1.
A further 23 trees sampled during a later visit were found to have died between and Table 2. As with site 4, a formal 1. However, inspections of adjacent ash stands revealed an absence of similarly well established symptoms, while nearby mature and ancient stands of ash did not have high levels of dieback and only a few apothecia were found underneath them. This 8 ha site that was established at the same time as site 5 in , and had similar site conditions. Details of the planting date and stock origins were the same as site 5. Subsequently the site had been sold and had not been thinned.
There was limited mortality and most of the dead trees were 1—3 m in height and estimated year of death ranged from to Table 1. Many near-dead, smaller trees had been girdled but still had epicormic shoots close to their root collars but largely hidden by the grass sward. Eleven of the smallest dead trees with typical ash dieback cankers were sampled Table 1. Many others had basal cankers consistent with longstanding H.
http://blacksmithsurgical.com/t3-assets/encyclopedias/pyfa-666-the-things.php Another indicator of a long established outbreak was abundant apothecia on both fallen rachises and small sections of woody material on the forest floor Kirisits et al. Table 1 shows the data for the 36 dead trees that were initially identified for investigation at the six sites.
Most of the planting stock had been obtained from UK nurseries and only the stock for the Devon site site 2 had definitely come directly from a non-UK source. Replacement stock was planted the year following establishment to make good any planting failures.
Apart from site 3, all the replacement plants were known to be sourced from the same nurseries that supplied the original stock. With the exception of site 1, all the sites had at least one tree that had died some years earlier with one or more diamond-shaped canker s on the stem consistent with the symptoms caused by H.
Although the planting date of most of the cankered dead trees was likely to be the initial establishment year, it could not be ruled out that some of the trees might be one year younger i. When a more detailed tree dating analysis was undertaken using a further 27 dead trees taken from sites 3, 4 and 5 Table 2 a similar pattern emerged, although the accurate counts of growth rings made in the laboratory indicated that the ring counts made in the field had underestimated the age of the trees and therefore the year in which they died.
As before, each of the 27 dead trees had at least one diamond-shaped canker on the stem indicative of H. Examples of the cankers are shown in Figure 2. The same section of stem had six sunken cankers, two of which had coalesced and each canker ranged in length from ca. Hymenoscyphus fraxineus was isolated from four of the six cankers demonstrating they were active lesions, and it transpired that all H. Despite the sunken and aged appearance of the cankers which were surrounded by high ridges of callus tissue, this proved to be deceptive when estimating canker age.
The depth of the cankers was largely due to vigorous growth and formation of wide growth rings between and from the uninjured cambium and phloem rather than multiple smaller growth rings over a longer period of time. Overall, four of the active lesions dated from ; one lesion for which H.
This suggests that the fungus is capable of remaining alive and colonizing stem material for upwards of 3—4 years after growing into bark tissue from infected shoots or foliage. Table 3 Timing of lesion development by Hymenoscyphus fraxineus on a single live Fraxinus excelsior log collected in Timing of lesion development by Hymenoscyphus fraxineus on a single live Fraxinus excelsior log collected in Of the remaining samples, twelve were negative for H. Additional definitive evidence for H.
To evaluate whether ash planted over the previous 20 years might have included any plants infected by the ash dieback pathogen, H. Ideally, sites needed to be relatively isolated and therefore unlikely to be affected by airborne H. If possible, study sites were also excluded with multiple planting episodes over the life of the plantation, to reduce the opportunities for the oldest trees on the site to be cross-infected by diseased stock introduced several years later.
Although the six sites selected for study established between and did not meet all these criteria completely, we were able to find evidence of infection by H. Moreover, based on the site characteristics, the most parsimonious explanation for the established infection is that it originated from use of infected planting stock rather than from airborne inoculum. In particular, the location and geographical isolation of sites 1, 2 and 3 in Northumberland, Leicestershire and Devon, made the likelihood of exposure to airborne ascospores from ash dieback outbreaks in mainland Europe very small.