There are 360 ​​days in a year. Eating lychees every day is not a dream.

What would it be like to sequence the lychee genome? It could allow you to eat it year-round.

Written by | Kestrel

In the ruins of the former Song Clan Ancestral Hall on Yinglong Street, Licheng District, Putian City, Fujian Province, there is the world's oldest existing lychee tree: "Song Jiaxiang". It sprouted as early as the Tianbao period of the Tang Dynasty (the same era when Yang Guifei ate lychees), and is now over 1,250 years old. If you happen to visit this ancient tree at this time, you may also have a chance to taste its fruit. Yes, although it has been vicissitudes for thousands of years, it still produces sweet lychees. Obviously, the place name "Licheng District" comes from this ancient tree, and lychees are also the main crop in the area.

Litchi is an evergreen tree of the Sapindaceae family. There are about 143 genera and 2,000 species of Sapindaceae plants worldwide, mostly distributed in tropical and subtropical regions, including 16 genera and 22 species of fruit trees, including longan and rambutan. There are two species in the genus Litchi, one is Litchi chinensis Sonn., which is native to my country; the other is Litchi philippinensis Radl., which is a local wild tree species with underdeveloped aril (fruit flesh) and no edible value. The lychees we are talking about today generally refer to the former.

The earliest record of human cultivation of litchi can be traced back to 3,000 years ago, but the origins of the domesticated varieties are unclear, which may be due to the complex agricultural history of litchi. Comparative genomic studies of wild and cultivated varieties show that the current cultivated varieties are not the result of a single domestication event. Earlier this year, Nature Genetics published a litchi whole genome sequencing analysis, the results of which showed that in history, people domesticated litchi twice in order to obtain fruit trees with different flowering periods.

At the beginning of the research, one of the authors of the paper, Jarkko Salojärvi, visited the ancient tree "Songjiaxiang".

Source
https://blogs.ntu.edu.sg/science/2022/06/01/understanding-breeding-history-of-lychee/

The research team analyzed the well-known "Fei Zi Xiao", a lychee variety that is a hybrid of early-flowering and late-flowering varieties. The researchers obtained a genome sequence of 470 megabase pairs and estimated that this accounted for about 96.2% of the complete genome. The genome was then annotated using RNA sequencing results, and then used as a reference genome to re-sequence the genome sequences from 72 trees, including 38 wild trees, to represent various variants of lychee.

Phylogenetic analysis of these genomes showed that litchi originated in Yunnan, my country, and then spread eastward and southward, spreading to Hainan Island about 18,000 years ago. Thousands of years later, people in the two places began to cultivate litchi: Yunnan people cultivated early-flowering varieties, and Hainan people cultivated late-flowering varieties. These were two independent domestication events. The two later hybridized to produce Feizishao and other varieties with flowering times between the two. The long history of cultivation has brought diverse litchi germplasm resources. The Guangzhou National Litchi Germplasm Resource Bank has more than 400 cultivated varieties (culitivar) of litchi.

According to the time of fruit maturity, cultivated varieties of litchi can be roughly divided into three categories: extra early maturing (EEMC), medium early maturing (EMC) and late maturing (LMC). Extra early varieties are very rare and have basically no industrial value. The best fruit quality always belongs to the late maturing varieties. The medium early variety may be artificially obtained by hybridizing the extra early maturing (Yunnan wild group variety, YNW) and the late maturing (Hainan wild group variety, HNW). Among them, Feizixiao comes from an extremely recent hybridization event because its inbreeding coefficient is negative, while its heterozygosity is as high as 2.27%. The so-called inbreeding coefficient can be understood as the probability that the two gametes forming the zygote come from the same ancestor; heterozygosity refers to the frequency of the allele in the heterozygous state at a certain gene locus. The higher the frequency, the more it indicates hybridization. In general, the diversity of cultivated varieties is higher than that of wild varieties.

Fig. 1 Phylogenetic tree of litchi based on single nucleotide polymorphisms (SNPs).

Although lychees are delicious, the harvest season is too short. 80% of lychees are produced in a short window from early June to mid-July. Moreover, lychees spoil quickly after ripening, and there is no way to freeze them like longans to ensure year-round supply. Is it possible for us to make lychees bear fruit in more time periods?

To this end, the researchers of this article also conducted in-depth studies on litchi varieties that bloom at different times to understand what kind of genetic mechanism controls the time of flowering. They found that the early flowering phenotype is associated with the deletion of a fragment of more than 3,700 base pairs. The earliest flowering litchi variety has both copies of this fragment missing in the genome, while the late flowering variety has two complete copies in the genome. The hybrid variety Feizixiao is heterozygous at this site, so the hybridization event that produced the Feizixiao variety should be recent, and may even be the first generation of hybridization (F1). In other words, the first generation of Feizixiao litchi (i.e. F1) was produced by sexual reproduction, but if it continues to reproduce sexually, it will produce trait separation, which is what we don’t want to see, so artificial asexual reproduction methods such as cuttings, grafting, and layering are adopted to preserve high-quality fruit variants. Because the generation time of litchi is long, it has mainly spread through asexual reproduction in the history of cultivation, so scientists can establish a relatively complete cultivation history model.

The researchers believe that the missing gene fragments of the early-flowering type they discovered can be used as biomarkers for the flowering time of litchi, which is very useful for breeders. In addition, the newly analyzed whole genome sequence can enable people to better understand other agriculturally useful traits and help people breed new varieties - even varieties with very different flowering periods from the original ones. If the flowering period of each new variety can cover all months of the year, then litchi may be available in the market all year round in the future - this is a dream that Yang Guifei dared not even think about.

Now is the season for eating lychees. There are so many varieties of lychees on the market. How much do you know about them? Here are some common varieties. Please leave a comment and do the questions! Based on the descriptions below, you can guess what varieties 1 to 9 are.

March Red

Sanyuehong is also known as Zaoguo, Yuhebao (Guangdong), Siyueli, Wuyuehong (Guangxi), and Lujiao (Sichuan). It is a famous early-maturing variety in Guangdong and one of the important fresh fruits exported in early summer in my country. It is distributed in the water towns of the Pearl River Delta in Guangzhou and the counties in southern Guangxi. It matures in mid-May in Guangdong (late June in some years) and early July in Sichuan.

The fruit is large, with an average single fruit weight of 26-42 grams. It is heart-shaped or skewed heart-shaped, with a rounded top that is slightly tilted to one side, a particularly large and slightly raised shoulder, and a particularly large stalk. The peel is thick and crisp, bright red, with large and flat cracks that are irregularly arranged, with flat lobes, and some cracks with small pointed lobes in the center. The suture line is not obvious. The flesh is white waxy, coarse and tough, juicy, sweet with a sour taste, with residue left after eating, and large lemmas that are mostly not full. The edible part accounts for 62-68% of the total fruit weight, and the quality is medium.

White sugar poppy

Baitangpeng, also known as Fengtangpeng, is a high-quality early-ripening lychee variety in Guangdong. It matures in late May.

The single fruit weighs 21.4-31.8 grams. The fruit is crooked or short crooked heart-shaped, with a round top, one flat shoulder and one tilted shoulder. The fruit stalk is thick, the skin is thin and bright red, most of the cracks are smooth, a small part is raised, most of them are slightly long quadrilaterals or polygons, large and sparse, irregularly arranged, the lobe peaks are thin and blunt, the lobe peaks near the pedicle and suture are thin and sharp, the cracks are shallow and obvious, and the suture line is not obvious. The flesh is white wax color, crisp, sweet and honey-scented. The seeds are medium-sized, and there are also small cores. The edible part accounts for 70-79.2% of the total fruit weight.

Concubine Smile

Feizixiao is also known as Luotangpu (Guangdong) and Luoti (Sichuan). It is one of the famous litchi varieties in Guangdong and Guangxi. It has a long history of cultivation and has been recorded in litchi chronicles of all dynasties. It matures in late May to early June, and in late July in Sichuan.

The fruit is large, with a single fruit weight of 23.5-31.1 grams. It is nearly round or oval, with a neat and beautiful shape, a round or blunt top, a high shoulder on one side and a flat and wide shoulder on the other side, and a thick and straight fruit stalk. The peel is thin, light red, with raised cracks of varying sizes, fine and dense lobes, sharp and piercing, fine and obvious cracks, and not very obvious suture lines. The flesh is thick, white wax color, crisp and juicy, sweet and fragrant. The seeds are small and mostly not full. The edible part accounts for 77.1-82.5% of the total fruit weight, and the quality is excellent.

Black Leaf

Black leaf is also known as black leaf and crimson shavings (Sichuan). It is a widely cultivated mid-ripening variety, widely cultivated in Guangdong, Guangxi, Fujian, and distributed in Taiwan, Sichuan, and even abroad. The leaves are dark green and almost black, so it is called black leaf. It matures in early to mid-June in Guangdong, late June in Fujian, and late July in Sichuan.

The fruit is medium-sized, with an average weight of 16.1-32 grams. It is ovoid or crooked heart-shaped, with a round or blunt top, flat or slightly raised shoulders, and a large stalk. The peel is dark red, thin and tough, and easily turns dark brown after picking, so it is called black-skinned lychee. The cracks are flat and large, arranged in a relatively regular pattern, with a horny cone-shaped small crack peak in the center of the crack, the crack is wide and obvious, and the suture line is obvious. The flesh is milky white, soft and juicy, sweet and slightly fragrant. The seeds are large and plump. The edible part accounts for 63.5-73.3% of the total fruit weight, and the quality is medium to high.

Chicken mouth lychee

The Jizui Litchi, also known as Xiangshan Jizui, is produced in Guangxi, with the main production area being Hepu, and there are scattered distributions in other counties. It matures in late June.

The fruit is relatively large, with an average single fruit weight of 29.5 grams. It is skewed heart-shaped or oblate, with a round top, flat shoulders or one shoulder slightly raised. The peel is dark red, thin and tough, with medium-sized cracks, flat or nipple-like protrusions, and arranged in a regular pattern. The peaks of the cracks are small and thorn-like, with shallow and narrow cracks and inconspicuous suture lines. The flesh is waxy white, crisp, sweet, and slightly fragrant. The seeds are mostly small cores. The edible part accounts for 79.3% of the total fruit weight, and the quality is excellent.

Cinnamon Flavor

Guiwei, also known as Dailu (Sichuan), is one of the most cultivated varieties in Guangdong Province and an important export fruit. Its export price is slightly lower than that of Nuomici lychee. It is distributed in Guangdong, Guangxi, Fujian, Sichuan, Taiwan and abroad. It matures in late June to early July in Guangdong and in late July in Sichuan.

The fruit is approximately round, medium-sized, and weighs 15-22 grams per fruit. It is rounded at the top, with flat shoulders and thin stalks. The cracks are convex and irregularly conical, with sharp and piercing peaks, obvious cracks and obvious suture lines. The flesh is milky, white, thick and solid, crisp, sweet, juicy, and has the fragrance of osmanthus. Most of them have small cores, but there are also large cores. The edible part accounts for 75.0-80.8% of the total fruit weight, and the quality is excellent. Among them, there are two varieties, the "Quanhong" Guiwei with bright red skin, and the "Yatou Green" with dark green spots on the shoulders and light red and green skin.

Glutinous Rice Cake

Nuomici is a rare lychee variety with the best quality and cultivated in Guangdong. It is mainly produced in the suburbs of Guangzhou, Dongguan City, Zengcheng, Panyu and other counties. It is also distributed in other counties. It is also planted in Guangxi, Fujian and other provinces (regions). In addition to fresh consumption, it is also the best for making dried lychees. It matures from late June to early July.

The fruit is relatively large, with a single fruit weight of 20.1-27.6 grams. It is flat and heart-shaped, with a neat shape, a round top, a raised shoulder, and a stalk that is obliquely 45 degrees to the shoulder. The peel is bright red, with obvious raised cracks, long and narrow, arranged longitudinally, with smooth crack peaks and obvious suture lines. The flesh is soft, smooth and juicy, with a strong sweet taste and a slight aroma. The seeds are small, mostly degenerate or hollow. The edible part accounts for 73.0-84.4% of the total fruit weight, and the quality is the best.

Hanging Green

Gualv is a well-known variety in Guangdong. The mother tree in Zengcheng Xiyuan is the most famous. Its descendants are not only planted sporadically in various counties in Guangdong, but also distributed in Guangxi, Taiwan, Sichuan and other provinces. It matures in late June to early July.

The fruit is nearly oval or nearly round, medium-sized, with a single fruit weight of 14.4-29.5 grams, with a round top, a slightly raised shoulder on one side and a slightly concave shoulder on the other side, and a large stalk. The peel is dark red with green, thin, with flat cracks, and the middle part is concave inward. The peaks of the cracks are hairy or sparsely pointed, with obvious cracks and obvious sutures. The flesh is white wax color, crisp, sweet and slightly fragrant, with plump seeds and slightly flat. The edible part accounts for 61.5-76.9% of the total fruit weight. Excellent quality.

Bamboo

Lanzhu is a famous variety cultivated in southern Fujian, mainly distributed in Longhai, Zhangzhou and Nanjing, and introduced in Guangdong and Zhejiang. There are two varieties, red and green. It matures in late June to early to mid-July in its place of origin.

The fruit is large, heart-shaped, with a round or blunt top, a slanted shoulder and a small stalk. The peel is thin, light purple or reddish with yellow or green; the cracks are medium-sized, with nipple-like protrusions, and a small crack in the center. The cracks are slightly pointed, the cracks are obviously narrow, and the suture line is not obvious. The flesh is milky white, soft and juicy, slightly astringent, moderately sweet and sour, and most of the seeds are burnt. The edible part accounts for 71.1-79.9% of the total fruit weight, and the variety is medium.

References

[1] https://www.the-scientist.com/news-opinion/genome-spotlight-lychee-litchi-chinensis-69634

[2] Hu, G., Feng, J., Xiang,

[3] Ni Yaoyuan and Wu Sufen, eds., Litchi Cultivation, Agricultural Press, September 1990

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