Breeding

by Don Hollingsworth
Winter 1995

With respect to the Itoh hybrids group cultivars (those from lactiflora seed parents and lutea hybrid pollen parents), the universally reported problem for breeding efforts is that the mating is highly incompatible, although not entirely so. For example, I have made hundreds of crosses with few seeds produced and no hybrid seedlings - those which grew all proving to have been from matings contaminated by unwanted pollens. Another time, from several flowers pollinated, I obtained five true hybrid seedlings all from two carpels having a total of eight seeds (this was the seed lot in which Paeonia 'Garden Treasure [Itoh group] appeared). Based upon this and subsequent observations, considering weather records of the days the pollinizations were accomplished, I hypothesized that there is a pollen incompatibility in the cross, which may be somewhat reduced when subjected to substantially above average temperatures during the time the pollen tube is growing. While this is not an established fact, the idea has thereafter guided my choice of priorities for expending effort in making the crosses.

So, when gathering materials with which to make such a difficult cross, one is well advised, I believe, to early in the effort obtain prospective parent plants showing favorable ornamental anatomy in both plant and flower, and, growth habits suitable to garden production and propagation. Having made such an all-inclusive statement, I must now say that I can not confidently tell you which of the many available clones are best for all of these purposes. That is, of course, where the "art" of plant breeding comes to the forefront. I feel competent, however, to speak to the question of selecting for ornamental characters, and, I feel, the utilitarian qualities tend to "come" when we have included a preference for parent clones which grow well and remain healthy under the conditions we can give them.

You have shared your intention to work in the area of red-flowered Itoh hybrid cultivars. Some observations about the flaws found in the redflowered clones so far produced may be useful to you. First the quality or hue of red.

Roy Pehrson (deceased) who made a prodigious effort with the Itoh cross around 25 years ago had opportunistically gathered pollens of flowers brought to the peony society exhibition. The pollens were mixed together and I am unaware whether the source cultivars were all recorded. Pehrson did share that pollen of Paeonia 'Corsair' (lutea group) was a major component of the mix. His efforts proved fortuitous in that he eventually obtained in excess of 100 hybrid seedlings, perhaps most of them from that particular pollen collection. We are fortunate in that he was also a mentor to others working on the cross, sharing his observations and divisions of seedlings. There is much to report on this that must wait. Now I will share what I believe to be significant observations concerning the achievement of desirable red color and improved doubleness in the hybrids.

We see a great prevalence of unappealing, dull red hues among a random batch of lactiflora group seedlings and most of the introduced cultivars. A reason for this has been offered by persons competent to do biochemical study of pigments. This is that the opacity, or density of flower hues seen in the most preferred of white and lighter pink flowered peonies is due to color factors which in the presence of red pigment results in dull, bluish colors. Red flowers dominated among Roy Pehrson's Itoh hybrid seedlings and they were almost all dull and drab in flower colors, very disappointing to most persons who had envisioned the expressions of red seen in the tree peonies. I believe it will be necessary to somehow get around this dullness in order to have red flowered Itoh hybrids which are appealing to most observers - in other words, to the "market".

lt is worth noting here that Pehrson had initially advocated the avoidance of pollen bearing lactiflora cultivars in a breeding collection, in order to reduce the risk of pollen contamination. He said that when he commenced gathering mother plants for his breeding project he chose lactiflora cultivars which were not pollen bearing and with generally normal carpels (principally of Japanese and anemone form flowers) and that he acquired, quite cheaply, a quantity of such kinds from the "close-out plants" price list of a specialist grower. He also reported that among his mother plants one of the best seeders for hybrid crosses was one of these which he referred to as Lavender Japanese, a characterization which, to me, invokes the image of "dull pink"! In retrospect I see two problems here - first, flower types having minimum doubleness - even the center petals are of small size, as contrasted with the widely available flower-in-flower form and larger petals of the fuller flower types, and, secondly, typically dulled colors.

Edward Auten (deceased) set out many decades ago to produce sharper red colors in the cultivars of Paeonia lactiflora. His early introductions (ca. 1930) include the single Paeonia 'Arcturus' (herbaceous hybrid) and Paeonia lactiflora 'Kickapoo'. These have fair color quality and are fine for their time and their flower type. However, I am seeking to add some of his later originations (ca. l 960). One of these I have now, Paeonia 'Maestro', a near shining spectrum red with semi-double to double form flower, which I hope will prove to have usable breeding fitness.

Another area of interest to me in the Itoh hybrids is increased doubleness. Except for multiplied petals and multiplied flower segments (as compared to the wild-type flower) - "multipetally" is a Pehrson coinage which I often use - the lutea hybrid tree peonies seldom offer much doubleness, while the few which produce pollen have low fertility. (Of those showing both fertility and substantial doubleness is Paeonia 'Alice Harding' [lutea group], pollen parent of the Itoh hybrids which were earliest to reach commerce.)

To obtain greater doubleness in the first generation Itoh hybrids, I believe we must look to the Paeonia lactiflora parents. The more double forms, even semi-doubles as in Paeonia 'Maestro', are more of a challenge to work with. However, these are amenable to favorable modification of the flower form upon deliberate effort, such that the carpels and stigmas will be improved and thereby having better anatomy for producing seeds. The "mechanics" of the procedure is to cut off the young shoots at a stage of growth when secondary shoots will arise from the remaining stubs. The "art" of the procedure is in the choice of timing. Cut off the new stems in early spring near or below the lowest normal leaf. Do so by the time they have reached 15-30 cm height, at a stage of development when the branch buds (axillary meristems) remain under control of apical dominance alone and before the onset of dormancy factors. This stimulates and enables the plant to regenerate stem growth from the branch meristems which occur at the leaf axials or further down-stem at the bud-cover axials. The secondary stems which grow afterwards will number from one to three or four per cut-off stem and some of them will produce a reduced flower (reduced in its doubleness).

That is the basic technique. You soon realize that the degree of success is variable and may prove to vary by cultivar and by other factors. The quality of the response perhaps partly reflects some optimum relationship between the amount of stored food remaining (at the time of pruning) and the number of secondary stems which are stimulated to grow. In this connection a report attributed to another deceased breeder of Paeonia lactiflora cv. Art Murawska, states he successfully produced seeds in normally sterile, doubled flower forms by pruning the spring shoots after having replanted divisions the previous autumn (presumably divisions of mature plants which would have flowered had they been left undisturbed). This might seem especially severe inasmuch as the process of dividing would ordinarily involve a reduction in the amount of stored food available to the shoots.

Pehrsons who report using the pruning technique sometimes associate the benefit with "stressing" of the plant, suggesting that something like the flush of fruiting often seen in a dying tree has been stimulated. A recent report by Steve Varner (APS Bulletin 292, Dec. 1994, p. 18) speaks of this in explaining the approach which he used in obtaining the recently registered peony, Paeonia 'Major Steve' (herbaceous hybrid), a seedling of the interspecies hybrid Paeonia 'Red Charm' (herbaceous hybrid). lt was long believed that Paeonia 'Red Charm' (herbaceous hybrid) was entirely infertile, but not obviously due to anatomy, inasmuch as its flowers typically have large carpels which appear to be normal (although the stigmas often have a poor receptive surface). Varner's result seems to support the idea that something more than apportionment of the remaining stored food is at work.

On the pollen side of the ltoh hybrids cross, I have little information as to the most reliable sources of fertile pollen among the red-flowered lutea hybrids. I grow only a limited selection of those presently in commerce and have had only a few of them under observation for pollen production. An inquiry to Dr. David Reath of the Reath Nursery (Vulcan, Michigan) may be productive in this respect, inasmuch as he has long been active in breeding among the lutea hybrids.

Of course, there is also the prospect of obtaining additional and possibly more desirable selections of red lutea hybrids pollenators using the red flowered Paeonia delavayi and, to seek enhanced doubling, by giving priority to the more doubled, red-flowered forms of the Paeonia suffruticosa cultivars as the other parent.

In all of the above, diligent effort, using as wide array of materials as can be assembled and making as many crosses as possible would seem to support the highest probability of success. Past experience shows that all the crosses and techniques discussed above yield poorly - lutea hybrid and Itoh hybrid, as well as the uncertainty of obtaining usable fertility in the more doubled flower forms of the cultivars of the lactiflora group. A larger number of crosses (using pollen which has at least some fertility) predicts better chance of success. I can report from personal experience that having a little success helps greatly to sustain one's enthusiasm.

Editorial Note of Donald Smith:
Roger Anderson has shared with me a few colored slides showing some of his recent "I" hybrid seedlings. One of these flowers was a beautiful bright red which appeared to be of excellent color (not dull at all). I believe it is the same one that appeared in his 1992 colored catalog/brochure which is called Paeonia 'Scarlet Heaven' (Itoh group). lt does not look to be a double, but the color does appear to be good. Maybe Roger has a record of the parentage of this one and would be willing to share it with the group.

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