Peonies: Their origin and micropropagation

Through our research with these plants, we have become particularly fascinated with a whole new group of peonies known as Itohs or intersectional peonies.   To understand this group of peonies, we must know a bit of peony taxonomy.  Peonies were originally grouped with the Ranunculaceae, the Buttercup family.  They now have their own family designation: Paeoniaceae, comprised of one genus: Paeonia.   The genus is made up of 3 sections: Moutan, which are known as tree peonies; Onaepia, which includes only 2 species of little commercial interest, and  Paeon, which are known as herbaceous peonies.

Family : Paeoniaceae

Genus: Paeonia

Section:
Moutan Onaepia Paeon
P. rockii P. brownii P. lactiflora
P. x suffruticosa P. californica P. officinalis
P. lutea P. peregrina
P. wittmanniana
P. tenuifolia

 

Peony cultivars are sold as being of P. lactiflora origin, as hybrid herbaceous (crosses within the Paeon section), as Chinese or Japanese tree peonies (referring to their origin and not botanical differences), or as hybrid tree peonies (crosses within the Moutan section).  To this we can now also add another category, the Itoh or intersectional peonies.  These are crosses between the Paeon and Moutan sections, more specifically, between P. lactiflora (herbaceous) and P. lutea hybrids (tree peony).

This cross was thought impossible until a Japanese nurseryman, Toichi Itoh, succeeded in 1948 by crossing ‘Kakoden’ (P. lactiflora) with ‘Alice Harding’ (P. lutea hybrid).  Unfortunately he did not live to see his plants flower.  An American, Louis Smirnow, purchased 4 selections from Itoh’s widow and introduced them to North America as ‘Yellow Crown’, ‘Yellow Emperor’, ‘Yellow Heaven’ and ‘Yellow Dream’.  These first hybrids are inferior from a horticultural point of view to the new Itohs now available, but they inspired a number of  breeders to attempt similar crosses, in particular Roger Anderson, Don Hollingsworth, Don Smith and more recently, Thierry Rat.

The Itohs have been available on the collector’s market for about twenty years, but prices of US$200 – $1000 for a 3-5 eye division kept them well out of reach of all but the wealthiest collectors.  High prices and lack of availability have made these varieties particularly attractive for micropropagation.

Peonies have a determinant herbaceous growth habit, meaning that next season’s growth is determined by bud and storage root development in the fall.  On herbaceous peonies, buds are located at the crown of the plant and protected by the soil.  On tree peonies, the buds are located on lignified branches above soil and often not protected by snow, therefore they are not as winter hardy as herbaceous peonies.  By the way, tree peony is a misnomer because they are really shrubs. Itohs have an intermediate growth habit with most buds at the crown, but often some on the lower part of the stem as well.

This determinant growth habit makes peonies recalcitrant to in vitro propagation.  Despite this, Planteck has developed an economically feasible method for the micropropagation of peonies.  Planteck’s micropropagation program has been successful with all three major groups of peonies: herbaceous, tree and Itohs.  Genotype still has an important role to play and some cultivars from each of these groups respond better than others.

The tree peonies generally multiply very well, but rooting is more difficult.  This is only natural given that tree peonies are usually grafted onto herbaceous nurse roots until their own roots are strong enough to take over.  The advantage of micropropagated tree peonies is that they are immediately growing on their own roots.  ‘High Noon’ was our first micropropagated tree peony to flower.

Given the infrastructure required for in vitro propagation, herbaceous cultivars which were developed in the first half of the 20th century and are readily available from traditional field propagation are not economically interesting for propagation by tissue culture.   However, new herbaceous varieties with high market potential are being bred and micropropagation has a definite advantage to bringing new varieties to the market more quickly and in sufficient number to meet the demand (and therefore at a more accessible price).  Once again, new varieties must first be tested for their response to in vitro propagation.  Eg. Mackinac Grand.

To date, all of our micropropagated peonies have flowered true-to-type.  Our first micropropagated peony flowered in 2003.  Since then  thousands of hundred have reached flowering size in our demonstration garden and with our customers.