A new fruit hybridized from lychee and longan, Su Dongpo and you both want to know

In 1100 AD, Su Shi was pardoned by the imperial court and returned to the mainland from Hainan.

As a famous "foodie", Su Dongpo ate wherever he went, even though he had a rough life, and left many literary works about food. When he was demoted to Huizhou, Guangdong, he left the famous poem " I can eat 300 lychees a day, and I am willing to live in Lingnan forever ", becoming the most famous lychee "seller" in history.

Friendly reminder: although lychees are delicious, you should not eat too many of them, or you may get "lychee disease" (Image source: theferns.info)

When Su Shi returned to the mainland, his first stop was Hepu in Guangxi. It was already the seventh month of the lunar calendar, and lychees (Litchi chinensis) were no longer in season. Even though Su Dongpo longed to eat them, he could not taste them again.

Fortunately, Su Dongpo welcomed the season when longan (Dimocarpus longan) matured.

The fruit is crystal clear when peeled, and the black and red core is faintly visible, which looks very much like an eyeball, hence the name "longan". It is a common fruit in my country and Southeast Asia (Photo source: foodnext.net)

Gourmet Su Shi is online again. After eating a full meal of longan, he left a poem titled "Lianzhou Longan is very delicious and can rival lychee":

"Longan and lychee, though different in origin, share the same ancestor. Just like sweet and tangerine, it is hard to compare them."

The general idea of ​​the poem is that longan and lychee are actually two different branches of the same category of fruit. Just like tangerines and oranges, it is difficult to tell them apart or to judge their superiority from their appearance.

It can be said that Su Shi was not only a gourmet , but also a careful naturalist . He keenly discovered the similarities and differences between longan and lychee. In today's plant classification, it is also proved that the two belong to the same family, both of which are plants of the Sapindaceae family.

In addition to the familiar lychee and longan, the Sapindaceae family also includes rambutan (upper right), grape mulberry (lower left), honeyberry (lower right) and other uncommon fruits. The Sapindaceae family is also a resource library with great potential for fruit development (honeyberry picture source: Tang Jingwei @PPBC, other pictures are from the Internet)

However, Su Dongpo could never have imagined that, a thousand years later, scientists have successfully hybridized lychee and longan. This fruit, which combines the sweetness of lychee and the freshness of longan, can now be served on the table.

It is actually very difficult to make these two species hybridize naturally in nature - after all, they are two independent species. However, there is another plant in the Sapindaceae family that is like a "stitched monster". Its fruit looks very much like a combination of lychee and longan. The ancient Chinese named it Dimocarpus confinis.

The fruit of the dragon lychee has the characteristics of both lychee and longan (Photo credit: Huang Jianghua @PPBC)

Since the dried longan fruit is often used as a traditional medicinal material, and the long lychee is very suitable as a rootstock for longan grafting, it was once widely planted in Guangxi, China. Its fruit has also been used to impersonate longan, but because the fruit of the long lychee is somewhat toxic , it is not suitable for consumption.

There was even a scene in an old TV series "Kangxi's Private Visits 2" where dragon lychees were used to impersonate longans.

Stills from the TV series "Kangxi's Secret Visits 2", in which there is a plot where dragon lychees are used to impersonate longans (Image source: YouTube.com)

Botanists once suspected that the longli was a species produced by the natural hybridization of lychee and longan. However, after gene sequencing, the truth became clear: the longli is less homologous than longan and lychee, and evolved earlier than the two. In layman's terms: the longli is not the "child" of the two, but the "grandfather" of lychee and longan.

The basic condition for species formation is that there are relatively obvious reproductive barriers with other species, and species will also use various means to limit exchanges with other species. This is the basis for a species to ensure the continuation of its own genes, but for scientists, this has become a "stumbling block" for breeding new varieties.

The homology between Longli and Rambutan is higher, but lower than that between Longan and Litchi (Image source: Journal of Fujian Agricultural Sciences doi: 10.19303/j.issn.1008-0384.2019.01.006)

The same is true for the hybridization of lychee and longan. Because the two are species of different genera, according to gene sequencing, the two began to diverge about 10 million years ago. The difficulty of making them produce "fruits of love" is no less than that of breeding hybrid rice. There are at least three huge difficulties waiting to be solved.

First of all, we need to understand the "family tree" of lychee and longan. The most basic condition for hybridizing two species is to have a good understanding of the parents. Although both are common fruits, they are tropical plants with a small distribution area in my country, so related research started late. Other countries' research on the two is also quite limited, and even the number of chromosomes in the somatic cells of these two plants is unclear.

There is a saying in the fruit industry that "the world's lychees are from China, and China's lychees are from Guangdong." On average, one out of every three lychees is produced in Guangdong (Image source: newsgd.com)

Thanks to the efforts of scientists, my country constructed the molecular genetic maps of litchi and longan respectively around 2010, and theoretically confirmed the possibility of hybridization between the two.

The next difficulty is to choose the right varieties for hybridization. China is the world's largest producer of lychees and longans, accounting for about 70% and 60% of the global output respectively. Especially lychees, China has formed a lot of varieties since ancient times. Guiwei, Nuomici, Feizishao... These are all familiar varieties. But this also brings "sweet troubles" to scientists. Which varieties are suitable for hybridization?

There are many varieties of lychees, and behind them are the efforts and dedication of countless fruit farmers and agricultural scholars (Image source: pdnews.cn)

After more than a decade of experiments, Chinese scientists chose Shixia longan as the female parent and Zi Niang Xi lychee as the male parent. Shixia longan can be regarded as the most delicious longan variety in China, and its yield is also considerable, but its fatal disadvantage is that the fruit is relatively small; while Zi Niang Xi lychee has a more resounding name: King of Lychees . It tastes not so sweet, but slightly sour, but its fruit is large, even larger than an egg, and its yield is very high.

After careful selection, these two varieties were finally chosen, not only because they have distinct characteristics and their advantages and disadvantages can form a perfect complement after hybridization, but also because Zi Niang Xi is a late-maturing variety, and its flowering period is shorter than that of Shixia Longan, so it can provide more vibrant pollen.

Crunchy Honey and its parent varieties (Photo credit: South China Agricultural University)

However, even so, if we want to achieve hybridization between the two, we still need to face a third problem: there is a lack of corresponding recognition mechanism between the hybrid parents, and under normal circumstances, longan cannot recognize the information of lychee.

The team from Huazhong Agricultural University used a technology called "induced pollination", which is a combination of physical, chemical and biological methods to enable longan to recognize litchi pollen and produce fertilized bodies.

Induced pollination is the most difficult step in the hybridization process, and because litchi pollen is very small, the work of pollination is like carving patterns on rice.

After continuous hybridization and screening, and 15 years of unremitting efforts, in 2022, Cuimi, a hybrid of longan and lychee, was officially launched in Conghua, Guangzhou.

Its peel is yellow-green, similar to longan, but with cracks like lychee. The flesh of the crisp honey is completely free of residue and has a sugar content of 20%-24%.

Comparing Crunchy Honey with its parent variety Shixia, it can be seen that Crunchy Honey's fruit peel is obviously cracked (Image source: South China Agricultural University)

According to people who have tasted the fruit, "After peeling off the skin, the flesh inside is full and contains a lot of water. Every time you take a bite, the crisp sound echoes in your mouth, leaving you with an endless aftertaste. The flesh of the crisp honey fruit is delicate and tender, and it is very enjoyable to chew."

Crystal clear, crispy honey flesh (Photo credit: South China Agricultural University)

In addition to its unique appearance and taste, hybridization also brings many advantages to Crunchy Honey. For example, it grows much faster than ordinary longan trees; it matures later than normal Shixia, which can form a staggered market launch; and its cold resistance is especially superior to its parents, which means that the planting area of ​​Crunchy Honey can spread northward.

Since there is "maternal inheritance" in the plant world, that is, the hybrid offspring's traits are more similar to the mother plant, so Cuimi is currently a variety of longan. But since Cuimi can produce stable and fertile seeds, we may be able to discuss whether it is a new species.

The emergence of Cuimi is just the beginning of cross-genus hybridization between longan and lychee. The team of Huazhong Agricultural University is not only trying more hybridization possibilities , but also cultivating seedless hybrid varieties .

Imagine: a fruit with the dual flavors of lychee and longan, without having to spit out the pit. This is simply the most anticipated moment of summer.

So, perhaps our final question is when will ordinary consumers be able to eat the Crispy Honey variety? According to reports, Crispy Honey has been promoted in some areas of Guangzhou through customized sales in 2023, and is expected to be fully launched in 2025.

This is also why we today are more fortunate than Su Shi: we feel the history of the past and witness the arrival of the future.

I wonder what kind of works Su Dongpo would create if he were alive today and tasted the crispy honey (Image source: Tiangong AI generated)

References

[1] Gezhi Lundao Forum. Sweet longan and lychee "married"? This marriage made me cry｜Liu Chengming. https://mp.weixin.qq.com/s/rVJfgbLi3PGtOAK_94lRAQ

[2] Nanfengchuang. Longan × Lychee =? The first new longan and lychee hybrid variety is born. https://mp.weixin.qq.com/s/-S6tl_SfpkkUPVUgOuMnuA

[3] Liu Chengming, Hu Youli, Fu Jiaxin. Research progress on the application of biotechnology in litchi and longan breeding and variety improvement[J]. China South Fruit Trees, 2003, 32(6):5.

[4] Zhao Yuhui, Hu Youli, Guo Yinshan, Zhou Jia, Fu Jiaxin, Liu Chengming*, Zhu Jiang, Zhang Mingjun, Obtaining and molecular identification of intergeneric distant hybrids between litchi and longan, Journal of Fruit Science, 2008, 25(6): 950-952

[5] Zhang Yongfu, Lu Bobin, Wang Ying, Pan Lijia, Hu Youli, Zhou Jia, Zhao Haiyan, Liu Chengming (corresponding author), Chromosome Observation of Some Rare Germplasms of Litchi and Longan, Acta Horticulturae Sinica, 2010, 37 (12): 1991-1994

[6] Jiang Fan, Chen Xiuping, Zheng Shaoquan. Phylogeny of Litsea cubeba based on ITS sequences of Sapindaceae[J]. Fujian Journal of Agricultural Sciences, 2019, 34(1):5.

[7] Guangzhou Radio and Television. “Crispy Honey” is finally here! Guangzhou’s midsummer fruits, “seamless” new arrivals →. https://mp.weixin.qq.com/s/JbZT9_6XID9AJjqafBrVhQ

Planning and production

Source: Bring Science Home (ID: steamforkids)

Editor: He Tong

Proofreading: Xu Lai, Lin Lin