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Hulthemia Roses and the Red Blotch

What are the heritable or genetic characteristics of the red blotch? Before proposing answers to that question, a short discussion about the Hulthemias is in order.

Roses are divided botanically into four sub-genera, with eleven main subdivisions in the subgenus Rosa. Hulthemia persica is placed in it's own subgenus, apart from the true roses, as are the subgenuses Hesperrhodos (containing R. minutifolia and R. stellata), and Platyrhodon (with one species from east Asia, R. roxburghii). Most species roses bloom just once each year in the springtime. Modern roses owe their ability to bloom repeatedly throughout the season to the China roses (Rosa chinensis). Through selective breeding, the recessive gene responsible for remontancy (continuous blooming) has been brought into modern roses. This selective process has occurred over many generations.

Hulthemia persicas, as the name suggests, originated in the area of ancient Persia, and can be found growing wild in the dry desert-like conditions of Iran and Afghanistan. There, because of its unattractive plant habit and thorny rambling branches, it is considered more of a weed than an interesting ornamental plant. Because of their similarities to roses, it was hoped that the hulthemias could be bred with roses to produce new hybrids. After a time then, just like horses were crossed with donkeys, attempts were made to cross roses with hulthemias.

Hulthemias however, as suggested above, are not true roses just like donkeys are not true horses. The hulthemias differ from roses in three very important ways: 1) they lack auricles, the little "ear-like" projections found at the base of each leaf stem where they join the cane; 2) they have simple leaves, rather than compound leaves seen in roses; and 3) they have a distinctive red blotch at the base of their petals, giving a unique red center to their blooms. It is this third characteristic that has intrigued rose breeders for more than 40 years.

Jack Harkness was the first to successfully hybridize roses with hulthemias. At first, work was very slow and like mules, the early hybrids were infertile and frequently unattractive. From his early work, Harkness ultimately released four of his hulthemia roses for introduction. Of these, ‘Tigris’ and ‘Euphrates’ were probably the most important. The other two were ‘Nigel Hawthorne’ and ‘Xerxes’. ‘Euphrates’ was a dead-end, meaning that it was completely sterile and not useful for further breeding. 'Tigris', resulted from a cross of Hulthemia persica X 'Trier', though sterile as a pollen parent, it had a low level of fertility when used as a seed parent. 'Tigris' then became the bridge for Harkness and other rose breeders to use to transfer the red blotch into roses.

During the last 10 years, the pace has quickened to get the red hulthemia blotch into roses. Several rose breeders from around the world have entered the race to produce attractive repeat blooming hulthemia roses. The most successful among this group includes Ralph Moore of the US, Chris Warner of England, Peter Ilsink of the Netherlands, and of course, the Harkness family of England. I predict that one of these men, or more probably, each of these men will have new repeat blooming hulthemia roses available for commercial introduction within the next five years.

So now, let's discuss the question of the red blotch. How is it inherited?

It appears that the "blotch" gene (or genes) is linked to genes coding for non-remontancy (that is non-repeat blooming), willowy growth, disease susceptibility and needle-like prickles. It also appears that there are several aspects of the blotch itself that may be independently coded for: blotch size and shape, blotch color, and intensity of color.

Hulthemias behave like most species roses and lack the capacity for repeat or continuous blooming. When introducing new desirable traits from non-reblooming species into modern roses, for example the hulthemia red blotch, it takes a minimum of two generations from species roses to re-establish the recessive trait for repeat blooming. 'Tigris' is once blooming and most of the seedlings coming from 'Tigris' also lack the ability to repeat bloom. These non-remontant roses can only bloom on wood from the previous year's growth. Therefore, unlike modern repeat blooming seedlings, which bloom 8 to 10 weeks after germination, 'Tigris' seedlings usually will not bloom until the second or third year after germination. This results in a very big delay in selecting the most desirable seedlings that have the best hulthemia-type red blotch. It also necessitates keeping a large number of seedlings to fully evaluate their blooming characteristics before inferior seedlings, or those with blooms lacking the blotch can be discarded. Of course those having a good blotch can then be selected. Once selected, those seedlings, if they prove to be fertile, can be used to further concentrate the genes for the red blotch in subsequent generations and combine that trait with remontancy.

My Experiences with Hulthemias

While I have had some success producing seedlings directly from 'Tigris', nearly all of my direct ‘Tigris’ seedlings have lacked remontancy. In fact, I have had only two seedlings from ‘Tigris’ that had blotches that were repeat blooming. Both of these seedlings had weak plants with very small blotches and ultimately died presumably from some genetic incompatibility. My best ‘Tigris’ selection came from a cross of ‘Tigris’ X [(‘Tobo’ X ‘Singin’ in the Rain’) X ‘Henry Fonda’]. It has a dark yellow bloom with a good red blotch on a better plant than ‘Tigris’. It has a good spring bloom with a very scant fall bloom, so it really is not a repeat bloomer. This seedling is code named "H65" and is still being used in attempts to produce a repeat blooming line from it. Hopefully, something interesting will come from the 417 seeds from crosses with it that are, as I write this, chilling in the refrigerator.

In addition to these hulthemia seedlings, over the last four years, I have had the opportunity to use important hulthemia seedlings from two very gracious and generous rose breeders. After many hundreds of crosses, I now have two fertile repeat blooming lines of hulthemia roses that I have begun crossing together.

The first hulthemia hybrid that I had the chance to bring into my own breeding program was English breeder, Chris Warner's variety, 'Tiggle'. This hulthemia hybrid is an important variety because in it, Warner overcame much of the disease proneness that is seen in the hulthemias. He did this by utilizing 'Baby Love' as the pollen parent crossed with ‘Tigris’. 'Baby Love' has excellent blackspot and powdery mildew resistance. In 2002, I made hundreds of crosses using 'Tiggle' both ways (as pollen and seed parent.) Nearly all of the crosses where 'Tiggle' was used as the pollen parent failed. However, there were two seedlings that clearly had 'Tiggle' as their father (pollen parent.) The first of these resulted from a cross of ('Chipmunk' X 'Halo Sunrise') X 'Tiggle'. My objective was to combine the "halo" developed by Ralph Moore with the red hulthemia blotch. That seedling exhibited growth very similar to 'Tiggle' - clean foliage with angular almost gangly growth, but it did not bloom for the first time until it’s third year in 2005. It was a disappointment to me because it bloomed only sparsely and the red blotch was much smaller and lighter than that seen in 'Tiggle'. The second seedling resulted from a cross of {'Halo Today' X ['Geisha' X ('Tobo' X 'Singin' in the Rain')]} X 'Tiggle'. This seedling also exhibited clean, powdery mildew resistant foliage, but had additional characteristics to qualify it as an important seedling for use in further hulthemia breeding. Besides being a fully repeat blooming hulthemia (it bloomed two months after germination and kept blooming throughout it's first year), it had a tidier bushy plant habit and most importantly, it produced hips. The hips proved to contain viable seeds. The blooms on this second seedling were larger than 'Tiggle', however, the blotch was much lighter and almost disappeared in warmer weather. Significantly, the red blotch is reliably passed on to it's offspring, though the germination rate is somewhat poor. This seedling was code named "G34".

My second line of hulthemias came about by using pollen from a fertile hulthemia hybrid from Mr. Ralph Moore. While visiting his nursery in Visalia, California, in 2004, he gave me six flower buds of his seedling code named "T33"*, a hulthemia hybrid having an excellent red blotch and from a cross of 'Tigris' X un-named Halo variety. From these six buds, I performed 109 pollinations, using 16 different seed parents, carried out over the next two days. The "take" using "T33" pollen was excellent, producing 79 hips, which was much better than my experience using 'Tiggle' pollen. These pollinations ultimately produced 946 seeds that were planted in January 2005.

A total of just over 300 of the seeds germinated. The majority of the resulting seedlings (approximately 75%) exhibited the typical gangly hulthemia growth, indicating non-remontancy (none of these bloomed in the first year). The remaining seedlings bloomed two to three months after germination, typical of modern roses. Unfortunately, almost all of these lacked any evidence of the hulthemia blotch. There was one group of four seedlings, however, all coming from the same seed parent, that did show the blotch and were repeat blooming. The seed parent of these was ('Orangeade' X 'Abraham Darby') X 'Midnight Blue'. One of the four, the one that exhibited the best blotch, fortunately also produced the most pollen. This seedling was code named "I89-2" and was used immediately in my breeding program starting in 2005.

So then, with two fertile lines of repeat blooming hulthemia hybrids, and many further crosses made in 2005, there were several new repeat blooming hulthemias that were found among the new seedlings in 2006. Of about 50 repeat blooming hulthemias, 30 have been kept for further evaluation and breeding. I am hopeful that in bringing several of these new hybrids together that it will be possible to concentrate and enlarge the blotch in the next generation.

The blotch itself seems to be transmitted as a dominant characteristic. What is not clear to me is whether the blotch is coded for by a single gene, or by multiple genes. The blotch varies considerable in size and intensity, and has been seen in various colors from orange, to red, to purple. Among the repeat blooming hulthemia seedlings that I have raised, blotch size has varied from barely a speck of red at the base of the petals, to blotches measuring about 1.5 cm in length. Some of the blotches have a clear demarcation of where they end, while others fade toward their edges and blend into the color of the rest of the petal. In every case so far that I have seen, the blotches are smaller and lighter in color during hot weather. If there are not several genes involved directly in coding for the blotch, there are certainly several genes that govern facets of its expression.

Though Hulthemia persica is reported to be diploid, or having just two members of each chromosome for a total of 14 chromosomes, repeat blooming hulthemia roses are probably tetraploid like most modern roses, meaning that they have four members of each chromosome (two coming from each parent), for a total of 28 chromosomes. If it is assumed that the hulthemia blotch is coded for by a single dominant gene with variable expression, it is probably reasonable to expect that the stronger the dose of the blotch gene, the stronger the size and intensity of the blotch. When one chromosome carries the blotch gene, it is likely that the blotch would be smaller than when two, three or all four of the chromosomes carry the blotch gene.

This story will be continued. From crosses made this year where there were repeat blooming hulthemias used as both the seed and pollen parents, I expect 1/4 of the repeat blooming seedlings to have a large enough dose of the blotch gene to have blotches comparable to the once blooming "T33" and 'Tiggle' hybrids.

Other Observations I Have Made

1. A large percentage of the repeat blooming seedlings coming directly from 'Tiggle' have blooms composed completely of smaller deformed petaloids. I wonder if there is some incompatibility between ‘Tiggle’ and modern roses. Luckily, I have not seen this problem showing up with seedlings of "G34".

2. Most repeat blooming seedlings coming from "T33" lacked any evidence of the red blotch. Only one seed parent produced good blotches in repeat blooming seedlings. That seed parent was from a cross of ('Orangeade' X 'Abraham Darby') X 'Midnight Blue'.

3. The hulthemia blotch differs from the halo of Ralph Moore’s HaloTM roses in several ways: the coloring on the halo goes farther from the apex of the petal towards the petal edges than in the middle of the petal, while in the hulthemias, it is farthest from the petal apex in the middle of the petal; the halo color often shows through to the reverse of the petals, while that is not so with the hulthemias – in fact, the hulthemias most often have a lighter color on the reverse side of their petals and; the halo color does not go all the way to the apex, but is separated from the apex by a zone lacking the halo color, while the blotch of the hulthemias often goes to the petal apex (though I have seen some of the hulthemia blotches cut-off from the petal apex by a zone of clearing, this probably represents an independent trait).

 

*"T33" was released in 2006 by Ralph Moore of Sequoia Nursery under the name ‘Persian Sunset’. Their website reports that "this variety is fertile, both seed and pollen, so may be of interest to breeders."

Resources:

Conversations and correspondence with Ralph Moore and Chris Warner

J. Harkness, Breeding With Hulthemia Persica (Rosa persica), American Rose Annual 1977

J. Harkness, Breeding with Hulthemia persica - Second Report, The Australian Rose Annual. pp. 117-119, 1989

Source regarding rose species: Original text from the article in Wikipedia, The Free Encyclopedia: List of Rosa species.

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