What are the remarkable tricks for breeding fruits and vegetables with high sweetness?

????? "Yuexin" strawberry, "Xingyun" sweet pepper, "Zengda apple" - these fruit and vegetable varieties are very sweet! Very sweet! Very sweet! Important things must be said three times! Generally, fruits and vegetables with a sugar degree above 10° are considered high-sugar (the international export standard sugar degree for apples is 12.5°). At present, high-sugar fruit and vegetable varieties have attracted more and more attention, thus invisibly enhancing the soft power of the varieties. Thus came the new domestic strawberry variety "Yuexin" with a sugar degree of 12.4°, the sweet pepper "Xingyun" with a sugar degree of 11.6° that can be eaten as a fruit, and the Zengda apple with a sugar degree of 16°, juicy and sweet.

Sugar degree: Under certain conditions (same temperature and pressure), the content of soluble solids in fruit and vegetable juice is directly proportional to the refractive index. Therefore, by measuring the refractive index of fruit and vegetable juice, the concentration of the juice (the amount of sugar content) can be obtained.

Refractometer: An instrument used to quickly measure the concentration or refractive index of sugar-containing solutions and other non-sugar solutions.

　　12.4°

"Yuexin" strawberry is truly sweet

From initially not adapting to the local environment, to later adopting greenhouse cultivation, strawberries only officially began their spring in Zhejiang. Counting the time, it has only been about 20 years. Today, "Zhejiang-produced strawberries" have risen to fame, but if we take stock, who has always dominated Zhejiang's strawberry greenhouses? Only then did we find that many are imported varieties from abroad. Among them was the "Toyonoka" strawberry mainly planted in the 1990s, while currently "Benihoppe" and "Akihime" are the most famous, together accounting for nearly 90% of the market share.

"Benihoppe" and "Akihime" were introduced from Japan. Their appearance, taste and early maturity are all superior. The only shortcoming is poor disease resistance. But now, with the emergence of the "Yuexin" variety, not only have these previous characteristics been retained, but disease and pest resistance has also improved significantly compared with the two main cultivated varieties.

What is commendable is that "Yuexin" was entirely bred by the Horticulture Research Institute of the Zhejiang Academy of Agricultural Sciences, meaning that the emergence of this local variety is expected to rewrite the pattern in which Zhejiang's strawberry stage has always been dominated by foreign varieties. Why is "Yuexin" so outstanding? In the view of researcher Jiang Guihua, a strawberry expert and deputy director of the Horticulture Research Institute, the key still lies in speaking through strength.

Jiang Guihua told reporters that in the breeding process of the "Yuexin" strawberry, the previous method of configuring hybrid combinations was changed, consciously selecting an elite line bred from a cross between European and American varieties and Japanese varieties as the female parent, and then crossing it with Japanese varieties, with the aim of both maintaining disease resistance and improving fruit flavor.

The seeds after hybridization need to be sown as seedlings, and which are superior or inferior is entirely determined by comprehensive performance. Only the most outstanding can become an elite plant and enter the next round of seedling selection. Passing through one hurdle after another, the breeding experts were delighted to find that the two elite plants that ultimately stood out after layers of selection had very striking trait performance: good early maturity, high yield, high sugar degree and strong flavor, reaching the expected breeding goals, and were identified as elite lines. In 2008, the preliminary breeding of this variety succeeded.

"In the subsequent characteristic verification trials, variety characteristic and cultivation trials, as well as the variety adaptability and cultivation trials carried out in Jiande and other places, compared with 'Benihoppe' and 'Akihime,' the advantages of 'Yuexin' were even more prominent," Jiang Guihua said.

The reporter once tasted "Yuexin" strawberries at the Haining Yangdu base of the Zhejiang Academy of Agricultural Sciences. Its appearance is light pink, and its taste is indeed sweet, and it is soft and juicy. Data from a professional testing institution of the Ministry of Agriculture show that its fruit total sugar reaches 12.4°, the highest sugar content among all tested varieties; results from previous comparative trials also show that from December to February of the following year, "Yuexin" strawberry has the highest soluble solids content, averaging 12.7%-14.2%, with the highest in February, reaching 17.8%.

It is understood that fruit flavor evaluation is mainly obtained through tasting, while specific digitization includes total sugar content, acid content and sugar-acid ratio. High-quality strawberries often taste sweet, slightly sour and have a rich flavor. How is sweetness detected? For convenience of measurement, it is usually based on soluble solids content, including sugar, acid and minerals, among which sugar accounts for the vast majority. Generally speaking, the higher the content, the sweeter it is.

Jiang Guihua introduced that through comparative trials it was found that not only in taste does "Yuexin" lead by a step, but it also has outstanding performance in disease and pest resistance. Its resistance to anthracnose, gray mold and aphids is clearly superior to "Benihoppe" and "Akihime." It is easy to raise seedlings, has a high survival rate and requires less pesticide. At the 2014 "Zhejiang Agricultural Guinness" strawberry competition, "Yuexin" also took first place with a fruit soluble solids content of 15.6%, stunning everyone on its debut.

But this "top student" named "Yuexin" also has shortcomings: the fruit skin is relatively thin and not suitable for long-distance transportation. Therefore, "Yuexin" strawberry is more suitable for short-distance sales in suburban areas and sightseeing picking. At present, "Yuexin" strawberry has been listed as a leading variety of the Zhejiang Provincial Department of Agriculture in 2016. Not only within Zhejiang Province, but also in major strawberry-producing areas such as Sichuan, Hunan, Shanghai and Beijing, it is absolutely a new favorite. (Reporter Zhu Haiyang)

　　11.6°

The positioning of "Xingyun": sweet pepper should be eaten as a fruit