I’ve probably asked similar question in years past so forgive me. My biology is weak and a bit dated, and I doubt simple Mendelian genetics can explain much, and assume an enormous number of genes come into play for most of the general features of a rose, but don’t know for sure…
To what extent does the phenotype matter more than the potential genotype of a rose when considering its use for further breeding? I’m wondering how much of the genotype (genetic potential) is expressed vs invisible when considering a rose for hybridizing. For instance, if K.O. is a very nice rose with good color saturation and higher drought tolerance than its sister Pink KnockOut, would one assume that Pink K.O. would statistically be highly unlikely to offer the better assets of K.O. in progeny? Any guidline as to how much less likely?
Similarly, I know I’ve asked, but I also wonder about the genetics of sports. Would e.g. “Burgundy Iceberg” offer a different set of genes to progeny than the original Iceberg? And if Awakening might be expected to be less fertile than New Dawn due to its doubleness, would there be any merit to using it over New Dawn if for instance one were angling for a more double seedling?
I assume that stable sports might be more likely to express mutated genetics, but unstable sports might have the same genes and just be flakey about expressing them or not?
Yes, some interesting traits may be “invisible”, but we don’t really know for sure. So we depedn on phenotype unless we do know. For instance if one gene for repeat bloom ought to be present based on parentage, we could hope that self seedlings would show some fraction around a quarter of repeat bloomers. But maybe not. We know it is a recessive trait, but it may also get scrambled during the formation of gametes, and could also be coupled somehow to a lethal trait. That is due to linkage disequilibrium. So for instance certain crosses tend to give offspring a lot more like one parent, for instance ins breeding with species. Mendelian genetics works only moderately well with roses.
As far as I know Pink K.O. is just a color sport of K.O. So very likely only the color trait will be differently inherited. And maybe not even that, if the sport leading to pink is not in the same layer of cells as those that make the pollen and egg cells. In general, sports do breed fairly true. For instance New Dawn yields a high fraction of repeaters while Dr van Fleet does not. My climbing Crimson Glory yielded climbing seedlings for instance. But crosses of large shrubs/climbers, with small bushes gives a mix of tall and short. Mostly it is not a single gene trait.
Sorry to be so wishy-sashy, but roses are polyploids mostly, so they have a lot of possible combinations to deal with. It gets really complicated really fast. So I go mostly by phenotype.
A number of years ago I had a “fun” time trying to sort out the inheritance of rebloom/non-recurrence in ‘Morning Stars’. According to Modern Roses V (1958) the latter is non-recurrent. However, it was raised from [(New Dawn x Autumn Bouquet) x (New Dawn x Inspiration)], and both ‘Autumn Bouquet’ and ‘Inspiration’ were from ‘New Dawn’ x ‘Crimson Glory’. It seemed odd that non-recurrence could be recessive.
Alas, ‘Morning Stars’ reportedly blooms in flushes, so my “deep thinking” on the matter came to nothing.
On the other hand, there is some mystery regarding ‘Cl. Mlle. Cecile Brunner’, which (according to Ralph Moore) can give both once-blooming climbers and reblooming dwarfs.
Actually, someone else (who used to work for a nursery) informed me that every year when they propagated ‘Mlle. Cecile Brunner’, they got three types: the reblooming dwarf, the reblooming shrub (Spray Cecile Brunner) and the once-blooming climber.
This is a complicated subject. Several years ago I had what seemed to be a great idea. I knew that David Austin had made good use of ‘Iceberg’ in the breeding of his “English” roses. So, I figured that ‘Burgundy Iceberg’ might serve as well, while giving more deeply colored offspring when crossed with, for instance, ‘Indigo’.
But once I had ‘Burgundy Iceberg’, I was a little disappointed with the floppy flowers, and did not go on with the experiment.
It is worth noting that ‘Burgundy Iceberg’ is a third generation sport: Iceberg > Pink Iceberg > Brilliant Pink Iceberg > Burgundy Iceberg.
It would be very odd if these changes involved three unique gene mutations. Maybe there was some chromosomal rearrangement (somatic segregation).
I think color intensity, rather than presence/absence is fairly easy to explain. Either there is a stable epigenetic conversion, or there is an insertion of variable length as in Huntington’s where it grows and grows and has more and more effect until it reaches a critical level. I don’t know of real evidence of either stable epigenetic conversions, or triplet repeat mutations in plants. But in a polyploid there can be a gene dosage effect. If white is a repressor of color, reducing the amount of the W factor will give more and more color. If there is a transposon causing the white, its loss from different copies of the modulator can result in up-regulating color production.
My favorite example of what white is about is with sweet peas. Two whites can yield a color, if the mutation in each white is for a different step in a pathway. If each diploid parent carries one copy of the gene to fix the defect in the other, offspring will have color, or white in a ratio roughly 1:3. Some (1/3 of) white offspring will breed true, others (2/3) will constantly give rise to colored offspring.
Color intensity modifiers are for real for sure. Rainbow KO is pale pink. Yet crossing it to other pinks, for instance Carefree Beauty, can lead to some of the most incredibly intense reds I’ve seen. OP or self crosses of either parent gives more boring pinks. Golden Slippers ( an orange, presumably pink on yellow) does the same with RKO.
All this is over my head, but may I ask a question(simple), If I have a yellow rose and keep crossing it with it’s self(totally away from any outside polination), will it go back to some of it’s parentage. Sorry to ask a silly question, but I had to ask. In other plants it appears we can work out what the outcome will be(might be), in roses this does not occur to the best of my knowledge. Is it because actual “background” to roses is not totally understood.
Okay… I’ve waded in over my head, so allow me to pose some questions for clarification…
Epigenetics involves gene expression, rather than genetic code, and theoretically would not be inherited in the context of this conversation.
Somatic segregation, as I’m understanding it, does involve the rearranging of chromosomes such that new pairs are created, and in plants, I am assuming that this can then involve the reproductive parts arising from the altered tissue (though I’m not entirely clear as to what happens with mitotic division and to what extent it matters for breeding purposes…)
I think these definitions may be a little different for animal biology.
An unstable sport, such as with Cecile B, would probably be the result of epigenetics, and the results of using one sport over another would for all intents and purposes probably not make a difference, whereas the sports to which Larry referred (New Dawn, Crimson Glory) might be Somatic segregation sorts(?) and would more likely be inheritable(?). I am guessing dwarfism is also generally a somatic mutation, but striping usually is not, for instance?
Would that be a correct interpretation? (And if so, could someone clarify how somatic segregation pans out in mitosis?
My impression is that the iceberg sports are quite stable, so I wonder if there is a rearrangement of the color expression/suppression genes that might be reflected in progeny.
Larry, you are correct. I didn’t realize Pink K.O. was listed as a sport. I find it inferior in many ways, and thought it was a sister riding on it sibling’s reputation. Oddly, for me, it seems less drought tolerant, but perhaps that’s location-related. The yard where I grew them has a huge range of soils.
David, my understanding is that, with roses, they are just way more complicated – having so many different species, routes of expressions, ploidies and such – so that predicting outcomes would be akin to successfully guessing a lottery winner. There are multiple genes that can affect any given trait, and that really muddies the water for Mendelian genetics. In theory, you could reinforce some traits by selfing a yellow plant over and over again, but the odds of selectively getting the genes from one parent in any seedling are slim to none. Plus, the seedling lacks half of the genes from either parent, having (typically) received one haploid from each. You will ultimately decrease the diversity of genes in those seedlings (homozygosity) potentially reinforcing negative traits while trying to segregate for positive ones. Inbreeding has it’s purposes, but requires judicious culling of stock that expresses negative recessive traits. (Anyway, that’s my interpretation – from a relatively biologically illiterate fellow member!)
I’m not convinced Iceberg and its variants are all that stable, Philip. Walking large wholesale nurseries growing thousands of each variant shows a wide variation in color intensity (in each type, not between types) and growth habit between plants of the same type. Finding dwarf, more vigorous (with greater prickle size and count) all the way to climbing (with even greater degree of large prickles) in “plain old Iceberg” from the same original source, is very common in my experience. Granted, perhaps multiple parent plants provided the bud wood for them, but walking rows from the same source, you have to select for gauge of wood and degree of prickles to get plants which will provide uniform plantings. The same goes for the pink and burgundy sports, just not to as extreme a degree.
Roses are a special problem. Tetraploids are messier than diploids. And often we don’t know the precise (or even the approximate) ancestry of desirable cultivars. For example, the dainty pink over white ‘Apache Tears’ (Karl Herbst x China Doll) would be a mystery if we did not know that ‘Karl Herbst’ was raised from (Independence x Peace).
Selfing a rose for a few generations could reveal some traits of its recent ancestors. And breeding with these inbred selections could make it easier to predict the sort of offspring to expect. Otherwise we can look to the ancestry (if known) and to the other progeny that have been raised from a variety we want to use for breeding. For example, ‘Karl Herbst’ can be used to breed deep reds, as well as delicate bicolors … even yellows.
As Jarebek (1975) commented, “In studying Modern Roses VII, I am amazed how often yellow seedlings come from crosses on ‘Pink Parfait’ and ‘Queen Elizabeth.’ Since most yellow roses are light on petallage, one might do well to reach into other color classes with yellow parentage. Even ‘Karl Herbst’ is listed as a parent of a yellow rose.”
BTW, it is also useful to make note of sports a cultivar has produced. There is ‘Yellow Queen Elizabeth’, so it should not be surprising that ‘Queen Elizabeth’ can give yellow offspring.
Speaking of sweet peas, here i Kraus (1916):
“A friend who is interested in Sweet-Pea culture crossed two varieties, a pink and a white. From the second generation he secured one form which he has termed an impure dominant. It is white with pink edging, and has given rise through seed to many forms, light pinks, dark pinks, whites, a glowing salmon and a soft salmon rose, this latter being the only form which has not proven variable on further testing. Three years ago this same impure dominant produced a node-sport, a beautiful glowing rose. Seeds from this sport produced the same rose-colored form, which has remained absolutely fixed. It is of interest to note that the impure dominant has produced similar pink forms which have not bred true.”
In roses, we have the added complexity of white-flowered species. These are capable of producing red pigment, but suppress the synthesis in the petals. These species (e.g., R. spinosissima, R. multiflora) can sport to various shades of pink and red. And when a white-flowered species is mated to another species (or cultivar) with pink or red flowers, it can be difficult to find any pure white progeny in later generations. These “white” selections tend to have some tint of pink.
This also can reverse the expected pattern of dominance. That is, non-red can be dominant over red. And then, two white-flowered varieties can give offspring with colored flowers.
It would be interesting to mate a white-flowered “variety” of a species that usually bears pink flowers, with a white-flowered species. For example, R. virginiana alba x R. spinosissima.
On the other hand, it might be possible to cross white-flowered varieties or different species to see whether the loss of pigment is due to disruptions at different points in pigment synthesis. E.g., Rosa rugosa alba x R. virginiana alba.
Sorry I didn’t have time last night to answer these messages.
One factor we have to remember is that the colored ICEBERGS are each propagated vegetatively, so that epigenetic changes are a perfectly good source of vegetative stable (or unstable as Kim observes) changes. Much harder to guess whether the color change carries into the next generation. If the original parent is diploid and we assume that the changed version (color vs white) is dominant. then a lot of the offspring with self would be colored (maybe 3/4). IN cross to another parent we just can’t say because we don’t know exactly what the color intensifier, or modifier (whatever we want to call it) is acting on. Tetraploids will give far fewer color offspring with if based on dominant change, because it will only be on one of 4 copies of a chromosome. The problem with regulators is you have to assume that both parents carry comparable things for it to work on. Depending on the other parent, that assumption may no be valid. Maybe different species have somewhat different regulatory pathways even if they have the same basic enzymes in the steps needed to make a color.
"Epigenetics involves gene expression, rather than genetic code, and theoretically would not be inherited in the context of this conversation. " There is debate and uncertainty over whether epigenetic changes can pass through the process of meiosis. Some people have evidence for erasing the marks and resetting function in each round of mating for animals. But there are some cases where the treatment of a parent affects children and maybe even grandchildren. For plants, hard to say.
I have harvested and grown OP from Carefree Sunshine (climbing or very vigorous version). A fraction come out exactly like the parent having gotten a balanced assortment of genes from both pollen and egg. Others are more intense, or pale, more double (very few) or more single(many). These OP are fertile and I’ll try for another generation. When I first started breeding roses I wrote to directors at several big nurseries. One wrote back, that they tried selfing as a way to make stable lines but found “inbreeding depression” with loss of vigor and self-sterility. The roses of the day (60s) were very dependent on heterosis (lots of mix and match to get the most vigorous). He discouraged me from trying the inbreeding route. ON the other hand Pernet-Ducher commonly used OP seeds of favorable crosses to get segregation in the 2nd generation. A fair number of good roses come from crosses of sibling pairs or OP selfs. Sometimes the pedigree on HMF is ambiguous.
And yet, corn breeders also faced inbreeding depression, loss of vigor and reduced fertility. These weaknesses were corrected by crossing between inbred lines.
Of course, corn breeders were aiming for uniformity rather than for novelty.
Some rose breeders have gone to later generations:
The Garden 56: 219 (Sept 16, 1899)
The parent of the above-named variety [Mme Eugène Résal] is Mme. Laurette Messimy. It was obtained by M. Guillot in 1887, being the result of a cross between an old China Rose named Rival de Pestum and the Tea Rose Mme. Falcot. We have in Mme. E. Resal a distinct proof of the fact well known to hybridists that the second and third generations of a cross often produce the best results.
Marie-Louise (Louisette) Meilland was not averse to some selfing:
‘Muchacha’ = [(Frenzy x Frenzy) x (Sangria x Sangria)]
‘Decor Arlequin’ = [(Zambra x Zambra) x (Suspense x Suspense)] x Arthur Bell
‘Anne de Bretagne’ = (Danse des Sylphes x Danse des Sylphes) x [(Zambra x Zambra) x Centenaire de Lourdes]
‘Concertino’ = [(Fidélio x Fidélio) x (Zambra x Zambra)] x Marlena
‘Golestan’ = (Tropicana x Tropicana) x (Seedling x Rouge Meilland)
‘Hidalgo’ = [(Queen Elizabeth x Karl Herbst) x (Lady x Pharaon)] x (Papa Meilland x Papa Meilland)
So, a little inbreeding is not too disruptive.