Hybridisation

Ulmus “Arcadia” (Patriot x Morfeo)

An exercise in elm hybridisation

Ulmus Arcadia seedling leaves

Ulmus Arcadia seedling leaves

Ulmus Morfeo

Ulmus Morfeo

Ulmus Patriot

Ulmus Patriot

Two of the best modern elm hybrids are the American “Patriot”, and the Italian “Morfeo”.  Neither is perfect.  Interestingly, their respective strengths and weaknesses are complementary.  From this, amongst other prompts, developed the idea of crossing them with a view to obtaining an elm which would ideally combine the best features of the two parents.

In 1980, Alden Townsend crossed the clone “Urban” [U. pumila x (U. hollandica “Vegeta” x U. minor)] with a Japanese elm cultivar later to be known as “Prospector”.  After testing, the clone was released in 1993 by the United States National Arboretum as “Patriot”.  It had proven highly resistant to elm disease in U.S. inoculation trials, it was fast-growing, and the literature described it essentially as a “tough tree”.   The U.S. market was initially told that Patriot had the talismanic “vase shape” of the American elm, but in fact its silhouette is much more reminiscent of the narrow-leaved elms of South Eastern England.

Morfeo, 20 years its junior, was obtained by Professor Alberto Santini’s team at the IPP in Florence from a crossing of the Chinese Chenmou elm with the Dutch clone 148, and is therefore [U. chenmoui x (U. hollandica x U. minor)].  Its growth rate is modest by the standards of hybrid elms, but the plant has demonstrated near-exemplary resistance to elm disease.  Morfeo’s cultural performance in plantings by the UK charity Butterfly Conservation has led it to become the most highly recommended modern elm assessed by that body.

The two clones’ strengths and weaknesses

Against Morfeo’s moderate annual height increment (approximately 150cm in ideal conditions) Patriot is capable of growing up to 250cm in a year.  However, Patriot tends not to put on sufficient girth to support this rate of growth.  Morfeo’s height/girth increment leads to much better balance, and the plant is sufficiently stable to free-stand from an early age.

Patriot, when well-grown, is strongly monopodial without being fastigiate.  Few hybrid elms display this desirable combination of characteristics, essential for the ultimate size and silhouette of the mature tree.  Morfeo is not reliably monopodial, and in England its leading shoot often adopts a recumbent position closer to horizontal than vertical (apparently less noticed in Italy).

Patriot’s foliage quickly matures from fresh green to the dark green of prototypical European elm, turning burnt gold in autumn.  Leaves are comparatively small.  These are positive attributes.  However, leaf stalks are lengthy, and the outline of the leaf is markedly shaped by pumila and japonica genes.  Morfeo’s leaves on the less vigorous shoots have strong European character, tending to be obovate with very short stalks, but the foliage has derived such dense pubescence from U. chenmoui that in certain lights it has a glaucous or even greyish cast.  It tends to lighten as the season progresses, and autumn colouration includes red and purple tones.

Patriot, like most prototypical European elms (apart from Wych elm) makes secondary shoots on the current year’s most vigorous growth.  In Morfeo this tendency is limited and sporadic.  The bark of Patriot on recent growth is grey/olive green.  That of Morfeo is brown.

Patriot is smooth-barked in its youth, and appears not to sucker.  Morfeo quickly develops semi-mature bark with isolated patches of corky flanges on young branches (derived from U. x hollandica, shared with English elm, and subjectively considered a positive feature).  It does sucker, so that the clone can maintain itself through successive generations without genetic recombination and the consequent risk of attenuated disease resistance.

Therefore, in addition to the optimal disease resistance to be expected from its parentage, the ideal Patriot x Morfeo cross would also exhibit:

(a)   Rapid growth combined with stability

(b)   Monopodial habit

(c)    Dark, short-stalked leaves with European outline and limited pubescence

(d)   Absence of red and purple autumn colouration

(e)   Secondary branching on current year’s growth

(f)    Early development of semi-mature bark

(g)   Suckering

 In February 2012 the London Borough of Islington planted two specimens of Patriot and Morfeo in Wilmington Square, in close proximity to each other.  Hybrid seed may one day be produced there.  Meanwhile, a controlled crossing has been carried out in Rochester, Kent, and is believed to be the first successful hybridisation of elm undertaken in this country for many years.  Patriot was chosen as the (male) pollen donor on account of its plentiful flowers, and Morfeo as the (female) pollen recipient since its flowers are large and fairly readily ripen into seed.  It should be noted that in past years there has been no evidence of Morfeo self-fertilising.

Ulmus Arcadia seedling leaves

Ulmus Arcadia seedling leaves

25 January Plentiful flower buds observed on 4 year old containerised Patriot.
28 January Seven flower buds observed on 6 year old containerised Morfeo.  The plant, initially much behind Patriot in its development, was immediately moved into a sealed but unheated conservatory.
4 February Patriot, soon to flower, was moved inside.  Over the next few days, pollen was collected and stored in a refrigerator  in a sealed container.
7 February Morfeo stigma lobes reflexed above emerging anthers.  Controlled pollination began, using a stiff brush to fire clouds of Patriot pollen at close range towards Morfeo flowers.  Repeated for a few days until Morfeo anther dehiscence.
24 March Morfeo seeds assessed as including some definitely fertile.
30 March Morfeo moved to a cooler room to prolong seed maturation.
7 April Morfeo seeds falling; all seeds immediately harvested and sorted.  10 were apparently fertile; these were de-winged and placed in an open plastic container between layers of soaked kitchen paper, maintained at a mean temperature of 25 degrees.
10 April First seed germinated.
11 April Three more seeds germinated.  Placed in pots of compost/sand/grit, covered with 5mm of same, and placed in dew-point propagator at 18 degrees and <100% humidity.
12 April Another three seeds germinated during the night, but dessicated before dawn.  Ultimately 9 of the 10 apparently fertile seeds germinated.  The three which dessicated overnight continued to extend their radicles notwithstanding the loss of the tips
13 April Seedling leaves open on the oldest of the plants.
29 May Axial buds breaking on stems of certain plants – infrequent with Morfeo.
18 June Seedlings provisionally assessed pending full description, individually photographed, and assigned identificatory codes AR 1-9 on the informal basis of earliest germination x apparent vigour.
23 June Preliminary description of each seedling undertaken.
AR1

AR1

AR 1

370mm.   Leaves dark green, matt, quilted, glaucous cast, alternate, markedly recurved downwards.  Coarse, blunt serration.  Sporadic and late development of side shoots towards top of stem.  Tip shows tendency to become recumbent.

 

AR2

AR2

AR 2

325mm.  Leaves dark green, alternate, moderately glossy, pronounced venation, lanceolate, curving upwards along axis of central vein.  Regular and balanced side-shooting, vigorous at base of plant.  Tip shows tendency to tilt

AR3

AR3

AR 3

340mm.  Leaves mid green, opposite, matt maturing to semi-glossy, delicate serration, rhomboid.  Regular, low-vigour side-shooting; leaves on side-shoots alternate, glossy and obovate without pronounced tips.  Strongly upright growth with no tendency to zig-zag or tilt at the tip.

AR4

AR4

AR 4

310mm.  Similar to AR 3, except for apparently lesser vigour, smaller leaf, and slightly more vigorous side-shooting.  Leaves on side-shoots lanceolate.

AR5

AR5

AR 5

330mm.  Leaves mid-green, alternate, matt, maturing to slightly glossy, some glaucous cast.  Lanceolate.  Held horizontally from the stem.  Side-shoots vary from average to high vigour.  Slight tendency to zig-zag/tilt at the tip.

AR6

AR6

AR 6

290mm.   Leaves dark green, alternate, maturing to very dark, glossy, lanceolate, with slightly undulate margin.  Very limited and uneven side-shooting at base and towards top of plant.  Zig-zagging at tip.  One leaf with a pronounced stalk.

AR7

AR7

AR 7

235mm.  Leaves mid-green, alternate, blunt serration, strongly recurved.  Very limited side-shooting at base of plant.  Zig-zagging at tip.

AR8

AR8

AR 8

235mm.  Leaves alternate, occasionally opposite, mid-green quickly becoming semi-glossy.  Strongly double-serrate with tendency to lobeing (assumed to be expression of a U. glabra gene).  No side-shooting.  Zig-zagging at the tip.

AR9

AR9

AR 9

215mm.  Leaves dark green, small, maturing to very dark, semi-glossy, alternate but occasionally opposite.  Leaf stalks apparent.  Strong venation.  No side-shooting.  Slight tendency to tilt at the tip.

 

 

 

 

 

The nine elm seedlings therefore show marked genetic diversity in terms of apparent vigour, leaf colour, form and ability to produce side-shoots.  Their full parentage is: [[((U. pumila x (U. x hollandica “Vegeta” x U. minor)) x U. davidiana var. Japonica] x [(U. chenmoui x (U. hollandica x U. minor))].  The Asian to European parentage is therefore in the ratio 5:3.

The plants will be grown on and observed.  Any which exhibit combinations of desirable traits will be vegetatively propagated in readiness for disease inoculation trials in or around 2017.

The likelihood of the ideal combination of genes occurring amongst so few seedlings is remote, but a plant combining stability and improved leaf colour while inheriting high disease resistance would have obvious usefulness.  The early observations reported above are broadly encouraging.

This Patriot x Morfeo progeny has been named Ulmus “Arcadia” after the region of Greece once famed for its forests, and for an idyllic landscape now lost.

For further information contact David Herling: info@resistantelms.co.uk

arcadia_seedarcadia_seed1

 

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