Do you know how this rare variety of peony was cultivated?

The Tang Dynasty poet Pi Rixiu once wrote a poem to praise the peony: "The national beauty is like drinking wine in the morning, and the heavenly fragrance dyes clothes at night." Since then, the peony has been known as "the national beauty and the heavenly fragrance."

Since the peony entered the palace from the wilderness during the Sui and Tang Dynasties, after more than a thousand years of hard cultivation by successive generations of breeders and gardeners, the peony has undergone a radical change from its original appearance in the wild, forming nine color systems of white, pink, red, purple, black, blue, green, yellow and complex colors, and thousands of varieties. Among these colors, white, pink, red and purple are more common colors in peony, while black, blue, green and yellow are relatively rare in traditional peony. Among peony lovers, there is often a saying that "black peony is not black, yellow peony is not yellow, and green peony is not green."

Light yellow 'Yao Huang' (photographed by Yang Yong)

Part 1

Is it possible that there is no real yellow peony in the world?

For a long time, it was a mystery whether there are truly yellow peonies. It was not until 1906 when French botanist A. Franchet published two wild peonies: Paeonia delavayi (purple peony) and P. lutea (yellow peony) that the botanical community first saw peonies with truly yellow flowers. Both wild species were discovered and collected by French missionary Delavayi in Yunnan, China. The yellow peony (P. lutea) was collected from Eryuan, Yunnan, and its flowers are golden yellow. After investigating wild peony resources in southwest China, botanists found that the distribution range of yellow peonies is extremely wide, and they are distributed in Kunming, Dali, Shangri-La, Deqin in Yunnan, and Linzhi County, Milin County and Bomi County in Linzhi City, Tibet. Only then was the mystery of the yellow peony unveiled.

At the end of the 20th century, Academician Hong Deyuan conducted a relatively systematic investigation and classification study of China's wild peony resources. The study found that there is no trait or combination of traits that can classify P. delavayi (purple peony) and P. lutea (yellow peony) into different species or even sub-species taxa. Many of the original taxa are just some extreme morphological variations of a species. Any morphological division is unnatural, so these two species and some other variant types are merged into one species: P. delavayi, or Yunnan peony. (Note: The "yellow peony" that appears below refers to the type of yellow flowers in Yunnan peony.)

Main flower color types of Yunnan peony (Photographed by Wang Fu)

Part 2

How are new yellow peony varieties cultivated?

Although wild yellow peonies have bright yellow flowers, they are very small and have poor adaptability. They are not resistant to high temperatures and severe cold, so the effect of direct domestication as horticultural flowers is poor. The small-flowered wild yellow peony is distantly related to the large-flowered cultivated peony in horticulture. Although they belong to the same peony group of the genus Paeoniaceae, they belong to different subgroups. The yellow peony belongs to the fleshy disc subgroup, while the traditional large-flowered peony (P.× suffruticosa) in horticulture belongs to the leathery disc subgroup. There is serious reproductive isolation between different subgroups, and it is extremely difficult to form seeds through hybridization. Even if seeds are formed, it is difficult to germinate. Therefore, Professor Maxime Cornu, a horticulturalist in Paris, once asserted that this species will achieve nothing in horticultural breeding.

But the slap in the face came too quickly. After Professor Victor Lemoine and Professor Louis Henry, who were contemporaries of Professor Maxime Cornu, cultivated yellow peonies from seeds, they tried to use yellow peonies as the mother plant and hybridize with traditional cultivated peonies (large flowers and highly double petals) introduced from China. After a lot of attempts and failures, Professor Victor Lemoine was the first to succeed in 1904 and hybridized the first yellow double-petaled large-flowered cultivated peony variety 'La Lorraine'. In 1908, Professor Louis Henry also succeeded and hybridized the yellow peony variety 'Souvenirdu Prof. Maxime Cornu' (Golden Pavilion), which has been widely circulated in the world so far. After that, Victor Lemoine and his son Emile Leomine successively cultivated many new yellow varieties.

'La Lorraine' (https://pivoinesriviere.com/produit/la-lorraine/)

'Souvenir of Prof. Maxime Cornu' (Photo by Yang Yong)

During the First World War, the new yellow peony variety of the Lemoine family appeared at the exhibition of the American Peony Society (APS), which caused a huge sensation and also led some American breeders to join the team of breeding new yellow peony varieties. Among them, the breeder with the most outstanding results was AP Saunders. Saunders realized that although the varieties bred by Lemoine had novel colors, most of them inherited the characteristics of the thin and weak pedicels of yellow peonies. The thin and weak pedicels could not support the huge flowers. Most varieties had the problem of drooping flowers, and some varieties even had completely drooping flowers, which greatly reduced the ornamental value. In order to avoid the problem of drooping flowers in hybrid offspring, Saunders chose traditional Japanese cultivated peony varieties with more upright and strong pedicels and mostly single or semi-double petals as the male parent to hybridize with Yunnan peony (both yellow and purple-red types).

Saunders also carried out a large number of hybridizations. Through continuous attempts and unremitting persistence, he finally announced his first yellow hybrid variety 'Argosy' in 1928. This is a yellow single-petal variety with side-opening flowers. After that, Suanders continued to expand the types of hybrid parents and the scale of hybridization, and new varieties continued to emerge. According to the APS list Peonies 1976-1986, Saunders and his daughter registered a total of 78 new peony varieties between 1928 and 1960. These new varieties inherited the characteristics of single or semi-double petals and upright pedicels of traditional Japanese peony cultivation. Most of them are single and semi-double petals, with enhanced upright flower heads and rich color variations, ranging from deep red, scarlet, apricot yellow to amber, golden yellow and lemon yellow. At this stage, some varieties cultivated by Saunders are still popular, among which 'High Noon' (sea yellow), a semi-double yellow flower variety, is widely cultivated around the world for its bright color, excellent adaptability and pleasant fragrance. This type of cultivated peony variety formed by hybridization between Yunnan peony and traditional cultivated peony is also called inter-subgroup hybrid of peony.

AP Saunders

(https://www.peonysociety.eu/some-new-hybrid-peonies-by-ap-saunders-1926/)

Above: ‘Argosy’ (https://www.hamilton.edu)

Below: 'High Noon' (Photo by Yang Yong)

Because Yunnan peony and traditional cultivated peony are distantly related, their first generation of hybrids (F1) are almost all highly sterile. During the decades that Saunders has been breeding yellow peonies, he has been trying to carry out hybridization between these F1 generations, hoping to obtain a strong yellow variety, but there has been no breakthrough. By chance, Saunders was patrolling in the garden and saw a full fruit pod on one of his hybrid F1 generations. He obtained two full seeds from this fruit pod. Saunders regarded it as a treasure, sowed it carefully and maintained it carefully. Finally, the two seeds germinated successfully and were cultivated into seedlings (Saunders F2A and Saunders F2B).

Saunders knew that he was too old to continue using these two precious F2 generations to cultivate new varieties of peonies. After careful consideration, he gave these two precious F2s to his friend William Gratwick, who also loved and owned a large peony garden. Gratwick knew the preciousness of these two peonies and took good care of them in his peony garden, and finally they bloomed successfully. Gratwick was not a stingy person. When his painter friend Nassos Daphnis came to his peony garden to appreciate flowers and sketch, he introduced these two precious peonies to Daphnis and encouraged Daphnis to use them for hybrid breeding attempts. Daphnis used these Saunders F2s to carry out a lot of hybridization work for many years. As Saunders guessed, these two F2 generations had certain fertility. They were used to hybridize with some of Saunders' F1s to obtain offspring. Dpahnis finally numbered more than 500 offspring, and since then the bottleneck of hybrid sterility between peony subgroups has begun to be broken. In recent years, with the efforts of many peony breeders, a number of new yellow peony varieties with stronger adaptability, more upright flower heads and fuller flower shapes have been bred through continued hybridization between fertile subgroups.

'Autumn Harvest', 'Big Sombrero', 'Pan' and 'Saharan Sun'

(http://solarisfarms.com/)

Part 3

Can the yellow peony flower color be inherited by peony?

After the yellow peony was cultivated, breeders began to think about whether it was possible to cross the peony with the herbaceous peony to pass on the yellow flower of the peony to the herbaceous peony, after all, the herbaceous peony is more cold-resistant and moisture-resistant and can be planted in more areas. However, although the peony and the herbaceous peony belong to the same genus, the herbaceous peony is a woody plant and the herbaceous peony. The huge differences in genotype and phenotype between the two made breeders believe that it was impossible to cross the peony and the herbaceous peony. This view was not broken until 1948 by Japanese breeder Toichi Itoh.

Itoh used the yellow peony intergroup hybrid 'Alice Harding' (金煌) as the male parent to cross-pollinate 1,200 peony 'Kakoden' (花香殿) and obtained 36 seedlings, of which 9 were more phenotypically like peonies. Unfortunately, Itoh did not see these offspring he created bloom during his lifetime. He entrusted these precious seedlings to his son-in-law to take care of them and they grew and bloomed successfully. Fortunately, these offspring perfectly inherited the yellow flowers of the yellow peony. In 1974, American businessman Smirnow brought four of the varieties ('Yellow Crown', 'Yellow Dream', 'Yellow Emperor' and 'Yellow Heaven') to the United States for breeding, and exhibited and sold them locally, which quickly caused a sensation.

To commemorate Toichi Itoh's pioneering contribution to inter-group hybridization of the peony genus, APS named the variety obtained with P. lactiflora as the female parent and the hybrid variety between peony subgroups as the male parent Itoh hybrid peony.

'Yellow Crown', 'Yellow Dream', 'Yellow Emperor' and 'Yellow Heaven'

(https://www.farmergracy.co.uk/products/peony-yellow-crown-bare-roots-uk

http://plants.makeitgreen.ca/11090002/Plant/8450/Yellow_Dream_Peony

https://pivoinesriviere.com/produit/yellow-emperor/

https://procvetok.com/zh/plants/perennials-yellow-heaven)

Itoh's breakthrough in hybrids between peony and peony groups has also stimulated many peony and peony breeders to conduct a large number of attempts. However, after all, peony and peony are too distantly related, so this type of hybridization is more difficult than hybridization between peony subgroups. After more than 70 years of efforts, there are only about 200 varieties of Itoh hybrids named worldwide. The male parents of these varieties are almost all hybrids between peony subgroups, and the two most frequently used varieties, 'Golden Era' and 'Golden Experience', are both yellow. Itoh hybrids perfectly inherit the advantages of hybrids between peony and peony subgroups. The flower and leaf shapes are similar to those of peonies, the ecological habits are similar to those of peonies, the flowering period is similar to that of peonies, the adaptability is strong, there are very few diseases, and the flowering volume is large. Therefore, compared with peonies, they are also promoted and planted in more areas, which also allows more people to appreciate the "national color".

Left: 'Golden Era'

Right: 'Golden Experience'

(https://americanpeonysociety.org/cultivars/peony-registry/)

Ito hybrid peony 'Bartzella' (photographed by Yang Yong)

Part 4

How is China progressing in yellow peony breeding?

Although China is the country of origin of Yunnan peony, the yellow peony was discovered at the end of the Qing Dynasty, the last feudal dynasty in China. The whole of China was in the midst of internal and external troubles. In the following decades, ornamental horticulture was almost stagnant. After the founding of the People's Republic of China, Chinese peony ushered in new development. After the reform and opening up, information exchange at home and abroad became smoother, and information on Yunnan peony breeding abroad was also introduced into China.

At the end of the 20th century, Li Jiajue's team from the Gansu Forestry Science and Technology Extension Station and Chen Dezhong, a senior engineer from Lanzhou Peace Peony Garden, first started the investigation and introduction of wild peony resources, and established a wild peony introduction and domestication base in Lanzhou. At almost the same time, Professor Wang Lianying's team from Beijing Forestry University also established an ex situ conservation base for the Paeoniaceae family in Luanchuan, Luoyang. Both bases collected and preserved Yunnan peonies in a relatively systematic manner. On the basis of successful introduction, they all carried out hybrid breeding work using Yunnan peonies and local characteristic peony varieties. Chen Dezhong, a senior engineer from Lanzhou Peace Peony Garden, hybridized yellow peonies with purple-spotted peonies, and in 2005, he bred the first new yellow peony varieties in China, 'Yan Huangjinmeng' and 'Huaxia Jinlong'; in 2009, Professor Wang Lianying's team also bred the first pure yellow and spotless new variety 'Huaxia Yipinhuang'. In the same year, He Lixia's team from Lanzhou Forestry Science and Technology Extension Station also bred a new yellow peony variety 'Huangjingjing' with purple spots.

All wild species of Yunnan peony are produced in China. We have unique resource advantages for breeding with Yunnan peony. Chinese breeders actively carry out surveys on wild Yunnan peony resources, and more excellent germplasm resources have been discovered and introduced. As these germplasm resources have been successfully used for hybrid breeding, more teams, such as Zhang Xiuxin's team from the Vegetable and Flower Institute of the Chinese Academy of Agricultural Sciences and Wang Liangsheng's team from the Institute of Botany of the Chinese Academy of Sciences, have also joined the hybrid breeding of Yunnan peony in the past decade. Now, new yellow peony varieties in my country are springing up like mushrooms after rain. In terms of Ito hybrid peony breeding, with the introduction of excellent foreign germplasm into China, China's yellow Ito peony breeding is also constantly developing. Professor Cheng Fangyun's team from Beijing Forestry University and Luoyang National Peony Garden have recently bred new varieties.

'Huaxia Golden Dragon' (Photo courtesy of Chen Fufei)

'Huaxia Yipinhuang' (Photographed by Wang Fu)

'Citrine' (Photo by He Lixia)

Main references:

[1]America Peony Society (APS). Peony registry. https://americanpeonysociety.org/cultivars/peony-registry/ [2022-3-16]

[2]Bigger, MD, et al., 1962. The Peonies. The American Horticultural Society, Washington.

[3]Hong, DY, 2010. Peonies of the world: Taxonomy and phytogeography. Royal Botanic Gardens, Kew, United Kingdom.

[4]Page, M., 2005. The gardener's peony: Herbaceous and tree peonies. Timber Press, Portland.

[5]Yang, Y., Sun, M., Li, SS, et al., 2020. Germplasm resources and genetic breeding of Paeonia: a systematic review. Hortic Res 7, 107. doi: 10.1038/s41438-020-0332-2. eCollection 2020.

[6] Li Jiajue, Zhang Xifang, Zhao Xiaoqing. 2011. Chinese Peony. Encyclopedia of China Publishing House, Beijing.

[7] Yu Xiaonan, 2019. Ornamental Peony. China Forestry Publishing House, Beijing.

Produced by: China Science Expo

Author: Yang Yong, Institute of Botany, Chinese Academy of Sciences

Reviewer: Wang Liangsheng Institute of Botany, Chinese Academy of Sciences

China Science Expo