Rose "Scarlet Meidiland"

Rosa "Meikrotal" (trademarked as "Scarlet Meidiland") is an extraordinary rose.

One of the new breed of landscape roses bred by the House of Meilland in France, it has flowers of such vivid scarlet intensity that it is difficult to photograph. It was released in 1988 and has been widely planted since then.

It is tolerant of winter cold and summer heat and resistant to pests and diseases. These qualities make it a good rose for mass planting along roadways etc.

The photograph here is one I took last summer in a heatwave: no rose symbolises summer heat better that this one.

The scent of roses in winter

Now winter is in its depths one great pleasure when viewing the barren landscape around is conjuring in the mind the scents of summer roses.

A little science

Rose scent is manufactured in the floral parts (petals usually, sometimes stamens) and released from specialised epidermal cells. The scent compounds (the so-called rose oils) are aromatic chemicals such as the rose monoterpenoids (e.g. geraniol) and rose ketones (e.g. damascenone). However there are very large numbers of chemicals that go to making rose scent, which accounts for the complexity and depth of the scent. In different roses these scents occur in differing proportions so giving the great variety of scents to be found in diverse rose varieties.

There are three major types of rose scent:

1. the classic Rosa gallica scent. In this the most abundant component is usually geraniol, as in the scented geranium (Pelargonium graveolens), and other deliciously fruity aromatic compounds;
2. the musk rose scent, a heavier scent of carotenoid-derived compounds
3. the tea rose scent, restricted to the china roses and their descendants. An important component of this tea scent is orcinol dimethyl ester [also known as 3,5-dimethoxytoluene]. Recent studies have shown that this is made by two enzymes, unique to tea roses, which methylate orcinol, first to orcinol monomethyl ester and then to orcinol dimethyl ester. The acquisition of these enzymes was therefore a crucial step in the evolution of the china roses.

The great rosarian G.S. Thomas wrote about roses with distinctive scents. Among these he mentions:

• Rosa bracteata - lemon
• Polyantha grandiflora - orange
• Adam Messerich - raspberry
• Vanity - sweet pea
• Ayrshire Splendens, Constance Spry - myrrh
• Fritz Nobis - cloves
• Lavender Lassie - lilac

These could all be due to a single dominant chemical. Orange and lemon scents are both due to the chemical limonene (different forms of the same chemical give orange or lemon). A raspberry scent might indicate the presence of raspberry ketone (hydroxyphenyl butanone). Sweet pea fragrance is due to the abundant production of linalool by sweet peas, the "rose myrrh" fragrance is said to be due to vinyl anisole, clove scent to eugenol, while a lilac scent might indicate the presence of the lilac aldehydes.

A rich and fragrant field of study!

Hurst's decaploid theory for the origin of rose species: wrong but not forgotten

C.C. Hurst (1870-1947) was the brilliant amateur geneticist who did more that anyone to elucidate the tangled history of the rose. He confirmed that the basic chromosome number of roses was 7 and he distinguished 5 rose genomes, A, B, C, D and E, each associated with a set of seven rose chromosomes. Diploid roses have chromosomes in pairs so they may be represented as AA or BB etc.

The basic building blocks of rose evolution are these diploids:

• the AA diploids: the odorata group (R. odorata, R. brunonii, R. moschata, R. multiflora etc)
• the BB diploids: the hugonis group (R. hugonis, R. wilmottiae, R. sericea)
• the CC diploids: the rugosa group (R. rugosa)
• the DD diploids: the woodsii group (R. woodsii, R. nitida, R. blanda etc)
• the EE diploids: the macrophylla group (R. macrophylla)

Roses exist not only as diploids but as tetraploids, pentaploids, hexaploids and octoploids. These can all be seen to be derived from the diploids by appropriate duplication and hybridisation. Thus Rosa nutkana and Rosa moyesii are both hexaploids but Rosa moyesii is (according to Hurst) AABBEE and Rosa nutkana is AADDEE. This is the accepted "upwards" theory of rose origins in which the polyploids derive from the diploids by chromosome doubling and hybridisation.

However, somewhat incredibly Hurst did not believe this. He put forward another theory: the decaploid theory. In this "downwards" theory roses derive from a hypothetical arctic decaploid AABBCCDDEE by progressive loss of genomes, ending up with diploids that have lost all their genomes except one!

No-one believed Hurst then and no-one believes him now. The upwards theory is based on mechanisms that are well attested in hundreds of groups of organisms, and is based on the diploids, all of which still exist. The downwards theory is based on a hypothetical decaploid that no-one has ever found and requires a mechanism that has never been demonstrated in any group.

So why did Hurst put forward his bizarre theory? He gives a variety of reasons:

1. the doubling of a sterile AB hybrid to give a AABB tetraploid would result in a homozygous plant whereas the roses are heterozygous.
2. the diploids occur in different habitats and regions and are not geographically available in the precise pairs necessary for hybridisation.
3. Hurst worked on the idea that polyploids were adapted to higher altitudes or higher latitudes than their diploid progenitors, therefore the polyploids would have to migrate northwards or up mountains very quickly in order to find habitat to which they were fitted.
4. Hurst also worked under the now defunct theory that the flora of the northern hemisphere had an arctic origin. Therefore it made more sense for arctic polyploids to become tropical diploids rather than vice versa.
5. Hurst thought that a single origin from one decaploid progenitor species was more parsimonious that multiple origins from multiple diploid species.

Today we can see that all these arguments are based on false assumptions. However, I don't mean to belittle Hurst because his theory proved to be false: he was a giant of genetics, who came up with a brilliant if erroneous theory: wrong but not forgotten.

[For a full list of Hurst's rose genomes see this link]

The artless pruner

Rose pruning often occupies a large section of rose books but all the advice boils down to:

• Shrub roses and climbers don't need pruning except to keep them in check, and some larger roses are best with light trimming only.
• Floribundas and hybrid teas should be pruned hard in early March (i.e. well before budbreak), in order to encourage the production of a few very vigorous shoots the following year which will bloom abundantly.
• "Pruning hard" means reducing last year's shoots to about four, each about 6 inches long with 3 or four buds.
• Cut 1/4 of an inch above a bud, with a sloping cut, sloping down away from the bud.
• Cut above an outward facing bud.
• Remove entirely dead wood and weak shoots; eliminate crossing or inward facing branches, giving an open centre.

And that is it. Or is it?

Many books obsess about the minutiae of pruning. A few years ago a British consumer magazine ran a test on rose pruning techniques, subjecting identical beds either to so-and-so's pruning method X or to thingummyjig's pruning method Y. And as a control, one bed was just run over with an electric hedge-clipper. The roses were then assessed in the summer to see which pruning method gave the best bloom.

Come the summer there was no difference at all. If anything the massacre with the electric clipper came out on top.

This sort of anecdote is music to the ears of all those interested in reviving the rose hedge, but do who not want to have to surgically prune a long hedge. David JC Austin has pioneered the modern rose hedge using his family's English Roses. He has used the fantastic, very vigorous "Hyde Hall" rose as a hedge, trimming it back to "half its size each year using a hedge trimmer".

Rose pruning has not come much further than the recommendations of Mrs Gore in 1838 (see below), except we now have the mechanical hedge trimmer!

From: THE ROSE FANCIER'S MANUAL; BY MRS. GORE (1838)

"OF PRUNING AND TRIMMING. Some gardeners prepare their rose-trees for spring-pruning by a preparatory one in the autumn; which is superfluous, except for the sake of neatness. The tree should be subjected to the pruning knife early in the month of March; and all dead, sickly, or unsightly branches carefully removed. The shoots of the preceding years should be trimmed down to the second eye, in order to secure fine flowers. A few species, however, require to have longer branches allowed; while others need only be trimmed of their sprays to produce an abundance of flowers. On this point, experience is the only guide; for the extent of pruning and trimming depends, not only upon the species of rose, but upon the situation, soil, and even the temperature of the season.

When it is desirable to retard the flowering of a rose-tree by two or three weeks, it should not be pruned till the vegetation has commenced, and the shoots have attained an inch in length."