Linli Hybrid Citrus

Linli Hybrid Citrus

Linli Hybrid Citrus is a protected geographical indication product.

　　Linli Hybrid Citrus is a new and premium citrus variety from Linli County, Hunan Province. It was carefully selected and cultivated under the guidance of experts from the Chinese Academy of Agricultural Sciences, the Citrus Research Institute of China, the Hunan Provincial Department of Agriculture, and the Citrus Research Institute of the Hunan Academy of Agricultural Sciences. Linli Hybrid Citrus matures and comes to market in mid to late December. It combines the characteristics of both mandarin oranges and sweet oranges, offering the nutritional flavors of oranges, tangerines, and grapefruits. It is a high-quality green fruit highly favored by consumers in the 21st century.

　　Variety Characteristics

　　Linli Hybrid Citrus has strong parthenocarpy. The fruit is flat and spherical, with a bright red appearance and easy-to-peel skin, making it convenient to eat. Each fruit weighs around 200 grams, with uniform size and good storability. The flesh is tender, juicy, seedless, sweet and refreshing, nutritionally rich, with a balanced sugar-acid ratio. It is high in water-soluble fiber, vitamin C, β-carotene, and selenium. Testing shows that its soluble solids content is ≥13%, total sugar content is ≥12%, edible rate is ≥78%, and vitamin C content is ≥55mg/100ml.

　　Growing Environment

　　Introduction to Linli: Located in the northwest of Hunan Province along the middle and lower reaches of the Lishui River, Linli County is the hometown of democratic revolution pioneer Lin Xiumei, founding father Lin Boqu, and literary giant Ding Ling. It is a national base county for commercial grain, cotton, and oil production, a national demonstration county for pollution-free agricultural products, a national standardized production base county for green food (citrus), a demonstration county for green food bases in Hunan Province, and a key citrus-producing county in Hunan. The county covers a total area of 1,210 square kilometers, with 18 towns (districts), 339 villages (communities), and a population of 456,000.

　　Climate: Linli County has a mid-subtropical monsoon humid climate, characterized by distinct seasons, short cold periods, long frost-free periods, changeable spring weather, less rain in summer and autumn, and little snow in winter. The annual average solar radiation is 106 kcal/cm², with an average annual sunshine duration of 1,629.1 hours, an average annual temperature of 16.4°C, an average frost-free period of 267 days, an annual precipitation of 1,253.1 mm, and a relative humidity of 81%. From April to June, there is abundant rainfall concentrated in this period, which is suitable for the growth of hybrid citrus branches and fruits. From September to November, there is less rain, ample sunlight, low air humidity, and large diurnal temperature variations, with monthly average day-night temperature differences exceeding 10°C, which is conducive to the accumulation of sugar and soluble solids in the fruit and color development. The unique climatic conditions are favorable for the high-quality and high-yield cultivation of Linli Hybrid Citrus.

　　Hydrological Resources: Linli County is rich in water resources, with abundant rainfall, crisscrossing rivers and streams, and high-quality water containing minerals and trace elements such as selenium, calcium, and iron, suitable for growing fruits like Linli Hybrid Citrus. There are 119 rivers of various sizes in the county, distributed in a dendritic pattern. The multi-year average runoff is 989.4 million cubic meters. The Lishui and Dao rivers flow from west to east across the county, covering 20.5 km and 44.6 km respectively, and together receive 110 tributaries of various sizes. The county has numerous reservoirs and ponds, with 151 small and medium-sized reservoirs built, with a total capacity of 265 million cubic meters. The main stream of the Lishui River features Asia’s largest turbine pump station—the Qingshan Turbine Pump Station—which has an average annual water lifting capacity of 120 million cubic meters.

　　Land Resources: Linli County has fertile land resources. The soil is mainly composed of Quaternary red clay, with deep layers, good permeability, and fertile texture. The soil pH ranges from 5.5 to 6.5. It is rich in trace elements such as selenium, iron, potassium, and calcium, and is a selenium-rich area. The terrain is mainly hilly and plain, interspersed with mountains. The hills and plateaus are contiguous and gently sloped, providing an excellent geographical environment for planting Linli Hybrid Citrus.

　　Environmental Quality: Linli County has dense vegetation, with a forest coverage rate of 42.1%. The air is consistently clean, and the water and soil are unpolluted, creating a favorable ecological environment for the growth of Linli Hybrid Citrus. The air quality in the Linli Hybrid Citrus production area meets the Ambient Air Quality Standards, soil quality indicators comply with the Soil Environmental Quality Standards, and irrigation water quality indicators meet the Agricultural Irrigation Water Quality Standards.

　　Production and Sales

　　Linli is rich in oranges and mandarins. According to the ancient text Yu Gong, citrus was cultivated in northern Hunan and other areas as early as 4,000 years ago during the Xia Dynasty. By the Song Dynasty, citrus had been widely promoted. The Anfu County Annals compiled during the Qing Dynasty’s Tongzhi era recorded that Linli citrus varieties such as “Niuzhu, Shitou, and Longzhao” were offered as tribute as premium fruits. In the 1980s, the Linli County Horticultural Demonstration Farm achieved a yield of over 10,000 jin per mu, setting the record for the highest single yield of citrus in Hunan. Citrus from Linli was rated as high-quality fruit in the province for three consecutive years. In the 1980s and 1990s, Linli County began optimizing its citrus variety structure. Through multiple introductions and improvements, it successfully cultivated a new citrus variety—Linli Hybrid Citrus—and promoted its widespread cultivation across the county. By the end of 2013, the planting area of Linli Hybrid Citrus reached 21,000 mu, with an annual output of 25,000 tons of fresh fruit and a production value of over 90 million yuan. With its bright red color, excellent quality, and unique flavor, Linli Hybrid Citrus is sold to major cities such as Shanghai, Guangzhou, and Xi'an, and exported to countries including Russia. In 2007, it won the third prize for “Hybrid Citrus Demonstration and Promotion” in Changde City; in 2008, it passed the national green product certification; in 2010, it won the first prize for oranges at the first Changde Citrus Tasting Competition; and in 2012, it received the award for the best-selling product at the fifth Changde Agricultural Products Exhibition and Sales Fair.

　　Cultivation Techniques

　　Proper Fertilization: Adult trees should be fertilized twice a year. The first application is in late June (around the 6th lunar month) as fruit-strengthening and shoot-promoting fertilizer, accounting for about 60% of the annual fertilizer amount. This should primarily consist of organic fertilizer, phosphorus fertilizer, or citrus-specific compound fertilizer, with minimal use of chemical nitrogen fertilizer. The second application should be immediately after harvest, accounting for about 40% of the annual fertilizer amount. Both ground applications should involve digging a circular trench 30 cm wide and 20 cm deep along the tree’s drip line for burial. In addition to these two ground fertilizations, foliar feeding can be applied as needed to quickly replenish nutrients.

　　Water Management: Timely drought resistance and drainage are essential. Fruit enlargement is highly sensitive to water supply. When leaves show signs of wilting in the afternoon but recover by the next morning, immediate watering or irrigation is required. Watering or irrigation should be done before 12 noon, using only “runner water,” and the field should be drained immediately after the soil is moistened. During the plum rain season, surrounding ditches, waist ditches, and plot ditches should be cleared promptly, and drainage should be enhanced.

　　Tree Pruning: The primary goal of pruning adult trees is to control canopy height, balance vegetative and reproductive growth, improve ventilation and light penetration, reduce unnecessary consumption, and lower pest and disease incidence. Pre-spring bud pruning should be done before the spring shoots emerge (before March 10), properly thinning out overcrowded, whorled, or crossing branches. Pre-autumn shoot promotion pruning aims to encourage uniform autumn shoots and should be carried out from mid-July to around the Great Heat period. Pruning mainly involves shortening healthy spring and summer shoots on the outer canopy and flower/fruit-dropped branches, typically cutting off 1/2–1/3 and leaving 5–7 leaves.

　　Reasonable Fruit Thinning: Linli Hybrid Citrus has a high fruit-setting rate. While proper management should be ensured to maintain tree vigor, chemical flower and fruit protection measures are not necessary. Due to its naturally high fruit-setting rate, special attention must be paid to reasonable fruit thinning. Otherwise, fruits will be small and taste poor, with degraded internal and external quality, severely weakening the tree’s growth vigor and stress resistance. Fruit thinning is a crucial technical management measure in Linli Hybrid Citrus production. Generally, the leaf-to-fruit ratio should be 50–80:1. Adult trees (planted at 111 trees per mu) should bear around 200 fruits per tree, with excess fruits thinned out. Thinning should occur from early May to mid-to-late August, targeting noticeably small or large fruits, outward-facing “upward-facing fruits,” deformed fruits, pest- or disease-affected fruits, and overly crowded fruits.

　　Pest and Disease Control: Strengthen management, carry out proper winter garden sanitation, and enhance tree vigor and resistance to pests and diseases. Promote integrated pest management and green control techniques, focusing on preventing and controlling citrus canker, scab, anthracnose, sooty mold, red spider mites, black citrus aphids, unaspis yanonensis, rust mites, and leaf miners.

　　Fruit Harvesting: Harvesting generally takes place in early December, choosing sunny or cloudy days after dew has dried. Use a two-cut method: the first cut removes the fruit with three leaves from the tree, and the second cut flattens the fruit stalk at the shoulder, ensuring the stalk does not touch the face. Handle fruits gently, strictly prohibiting throwing, dumping, using non-compliant baskets or crates, excessive vibration or compression during transport, and exposure to sun, dew, or rain. Do not mix diseased, deformed, damaged, or fallen fruits with others.

　　Linli Hybrid Citrus

　　 The administrative regions of 15 towns in Linli County, Hunan Province: Jiuli Township, Guanting Township, Xin’an Town, Wangcheng Township, Yangban Township, Wenjia Township, Fenghuo Township, Xiumei Town, Shanban Township, Taifu Town, Chen’er Township, Baizhi Township, Sixinggang Town, Shiji Bridge Town, and Tingxian Ferry Town.

　　 “Request from the People’s Government of Linli County on Delimiting the Protected Geographical Indication Product Area of ‘Linli Hybrid Citrus,’” Lin Zheng [2014] No. 129.

　　 Enterprise Standard of Linmei Fruit Industry Farmers’ Professional Cooperative in Linli County: Q/KWDG018-2012 “Linli Hybrid Citrus.”