2015 hybrids and progress report
FL 493 x U. minor “Tonge Mill”
Back-crossing, as described last year, aims to combine the resistance of a modern elm clone with the appearance of a strain which has traditionally grown in this country. The goal is to produce a substantial progeny of seedlings which can be expected to range between the extremes of those which have neither the resistance of the one parent nor the looks of the other, and those – even one would be a significant development – which have resistance and aesthetic qualities in the ideal combination.
In early 2015, two plants of the highly resistant and vigorous FL 493 (of 75% European elm parentage) developed copious flower buds, and unlike last year, they developed quickly and evenly. Flowering twigs were obtained once again from the stand of U. minor growing at Tonge Mill, Sittingbourne, which combines attractive form with a degree of disease resistance.
The cross-pollination attempt led to perhaps 10% of seed proving fertile. The germination rate was high, and some 95 seedlings emerged. They showed obvious genetic variation from an early stage, including differences in vigour, leaf shape, colour, tendency to produce paired leaves, recumbency of growing tips, and onset of side-shooting. Broadly, the appearance of most at this stage seems closer to the male Tonge Mill parent than to FL 493.
At the time of writing (2 June 2015) the tallest of these seedlings have already reached 30 cm.
Only time and testing will establish how much of FL 493’s disease resistance has been inherited. However, on the principle that resistance is normally within the parental range, there is good reason to hope that a progeny of this size will include at least one or two clones of real interest.
FL 493 x Patriot
The second of the two flowering FL 493 was fertilised with pollen from the resistant American hybrid “Patriot”. For a period, the quantity of flower on this specimen of FL 493 was such that the plant’s survival seemed to be in question. The ultimate proportion of fertile seed was only about 2%, probably because of the stress of this excessive flowering. About 80 fertile seeds germinated, but some later damped off. This progeny is less vigorous than the one described above. That seems curious since Patriot is a notably vigorous plant. It probably reflects the fact that it was unfortunately necessary to set out the seeds in trays rather than individual pots, as was done for FL 493 x Tonge Mill (and transplanting them at the end of this year will further check their development).
Given that both parents of this progeny are disease resistant, it seems likely that their offspring will include plants which show good resistance in future inoculation trials. These are planned for 2018 or 2019, and a site has already been identified.
Patriot x FL 493
A by-product of the above cross was its reverse, since FL 493 pollen happened to fertilise a few flowers on the Patriot plant which was in use as a pollen donor. A few apparently fertile seeds were harvested, but none germinated.
FL 506 x FL 493
Since one plant of FL 506 had a few flower clusters, the attempt was made to fertilise them using pollen from FL 493. One fertile seed was produced, which put out a vigorous radicle but then succumbed to rot in over-wetted compost.
2014 hybrids – progress report
FL 462 x Patriot
This cross, undertaken only because the materials were to hand, was initially puzzling because so little genetic variation appeared. Of the seedlings which survived the onslaughts last year of wind, drought and sooty mould, 11 were retained and the rest planted out. This year, genetic variation within this progeny is very obvious. Last year, very few of these seedlings showed good stability; this year, most have survived an ever windier spring than usual unscathed. None of these plants currently seems strikingly handsome, but most of them will be kept for future inoculation testing.
Morfeo x Sapporo Autumn Gold
The crossing of these two highly resistant clones took place last year with insufficient Sapporo pollen, but produced two seedlings. Both exhibited twig die-back, perhaps due to the U. pumila (Siberian Elm) genes in Sapporo. One of the two trees this year is fairly bushy and amorphous, and has very light green foliage. The other is moderately shapely, quite vigorous, and dark green. It has inherited none of the glaucous character of Morfeo’s parent U. chenmoui, and if it proves to be disease resistant it could be a useful tree. It seems relatively easy to propagate, at least from early indications.
Morfeo x U. minor “Tonge Mill”
The rather sorry story of this first back-cross is given in full in last year’s hybridisation report. The sequel is more cheering. Following this single seedling’s rocky first year, it has developed during the first part of this season into quite a good-looking tree. Its vigour is now moderate (last year it was lamentable), its form is attractive, and the foliage colour is considerably better than it was last year. The fact remains that it back-crossing a large progeny is needed for there to be much chance of an ideal combination emerging, and this turned out to be a progeny of just one. Nevertheless, whatever its ultimate disease resistance, at least the plant is no longer quite the disaster it first appeared to be.
This batch of seedlings was fairly ruthlessly reduced to just four, selected for looks, form, vigour, and above all, the impressive girth increment shown by some. Two of the plants coincidentally suffered damage to their leading shoots, so that their form is currently difficult to assess. The colour of a couple of them is notably light. Of particular interest is the fact that the “exoniensis twist”, which frankly disfigures Columella, seems either to have disappeared or at least to be greatly attenuated in these seedlings. The question is how much of Columella’s exemplary disease resistance may have gone with it.