Cui Mi, the world's first longan-lychee hybrid variety, is ripening and is expected to go on sale starting mid-September. [Photo/China Daily]

Professor Liu Chengming introduces Cui Mi's breeding process in Guangzhou, Guangdong province. [Photo/China Daily]

The world's first longan-lychee hybrid variety named Cui Mi, or Crispy Honey, is ripening and is expected to go on sale starting mid-September, further diversifying fruit varieties in the domestic market.

"Having weathered three straight winters of frigid extreme weather, researchers have conquered frost impacts via cultivation innovations and secured consistent fruit yields this year," said Liu Chengming, a professor with the College of Horticulture at South China Agricultural University in Guangzhou, capital of Guangdong province.

With its uniquely crisp and sweet taste, as well as the merit of late-maturing off-season ripening, Cui Mi will further diversify the fruit industrial structure and emerge as a new cultivar that helps raise farmers' incomes and fuels rural vitalization in Conghua district in the southern metropolis in the months to come, said Liu.

"It is crisper and sweeter than lychee, and more aromatic and tender than longan, with absolutely no fibrous residue," he said.

Cui Mi was developed through distant cross-breeding, with Shixia longan as the female parent and Ziniangxi lychee as the male parent. Both Shixia longan and Ziniangxi lychee are local varieties.

"Compared with Shixia longan, Cui Mi delivers twice the yield, boasts stronger cold resistance, and ripens 15-20 days later," he said.

However, Liu explained that Cui Mi is still only available for limited trial sales at present. Priced at 76 yuan ($11.26) per kilogram online, the total output for this year stands at merely several metric tons.

The variety is currently being cultivated across a little over 2 square kilometers in locations including Guangdong's Guangzhou, Qingyuan and Chaozhou cities, as well as Luzhou in Sichuan province and Dali in Yunnan province, said Liu, who has led a team focused on longan-lychee cross-breeding research for nearly 20 years.

By comparison, China's longan cultivation area tops 2,666.67 sq km.

According to Liu, Cui Mi's yield is expected to exceed 25 metric tons next year, and prices will likely drop after a mass launch.

"By August to October next year, consumers will be able to purchase Cui Mi through a much wider range of shopping platforms," he said.

Zungly Agricultural Group, a local agricultural product sales company, has been entrusted with the market-oriented promotion of Cui Mi. Adopting the "enterprise + cooperative + farmers" model, the group provides seedling stocks and technical support.

Ji Ge, manager of the Conghua plantation base, said while Cui Mi resembles longan in appearance, closer inspection reveals how its rind is covered with distinctive crack-like patterns.

Unlike local traditional longans that hit the market mainly in summer, Cui Mi features a delayed ripening period with a greatly extended harvesting cycle, Ji said.

Guangzhou Liding Eco-Agriculture Development Co began grafting Cui Mi in 2020, with a small crop set in 2021.

Liu Ruibo, manager of the company, said the fruits of this year's harvest are larger and sweeter, with thicker flesh, than the crop from previous years.

"Its high-yielding performance remains unchanged, still expected to exceed 15 tons per hectare," he said.

In addition to the plantation base in Conghua, Cui Mi is growing well in other plantation bases and is expected to redefine China's longan planting geography.

According to Liu Chengming, in Qingyuan's Lianzhou plantation base, covering an area of 66.67 hectares and located merely 45 km from the border with Central China's Hunan province, where extreme winter temperatures range from — 7 C to — 3 C, Cui Mi will mark its first bulk fruiting this year, with ripeness expected in early-to-mid-September.

More encouragingly, in high-altitude trial plantation bases at 1,800 meters above sea level in Dali and Lijiang, Yunnan, with typhoon-free conditions, no frost and large diurnal temperature differences, Cui Mi is now growing well and delivers exceptionally outstanding aroma, crispness and tenderness, he added.

Hampered by strong reproductive isolation, intergeneric longan-lychee hybridization has long baffled breeders.

Since 2007, Liu's team has worked to break the bottleneck and invented mentor-pollination technology after about three years of research.

Longan tissue extracts and special chemicals are used to treat female-parent stigmas to enable pollination and fertilization, said Liu. Through molecular-marker paternity verification and multiyear superior-plant screening, 69 true hybrids were picked from more than 100 progenies.

SZ52, a high-quality late-ripening elite strain, was designated Cui Mi after Guangdong's 2022 on-site variety appraisal and obtained official variety certification in 2023.

Just as citrus fruits achieve year-round supply thanks to their diverse varieties, Liu said he holds an even longer-term vision. "We can have freshly harvested longans and lychees available for nine months each year. And I believe this would be an immensely meaningful achievement."

Currently, longan and lychee can be harvested over a two-month period in summer.

Lychee and longan, together with banana and pineapple, are regarded as four major typical fruits in South China and play a big part in Guangdong's agricultural production and development.