Introduction Performance and Key Cultivation Techniques of the Blueberry Variety Bluetta

Introduction Performance and Key Cultivation Techniques of the Blueberry Variety Bluetta

As an emerging small berry, Vaccinium L. is gradually attracting more attention from more investors due to its special nutritional value, and its planting area and yield are also increasing rapidly. The commercially cultivated Vaccinium is mainly the blue-fruited type, also known as blueberry. The cultivars currently used in production in China are all introduced from abroad. Some cultivars, such as Meiden [1] and Northspring [2], are suitable as processing raw materials for jam, while some cultivars, such as Bluecrop and Duke, are more suitable as fresh-eating fruit [3]. With the continuous development of the planting industry, the demand for cultivar diversity is also increasing. The introduction of new superior cultivars has practical significance for enriching China's Vaccinium fruit market and expanding the scope of cultivation.

1 Introduction trial process

Bluetta (formerly named Bluetta) is a cultivar bred in 1968 through cooperation between the United States Department of Agriculture and the New Jersey Agricultural Experiment Station. Its parentage is (North Sedwick x Coville) x Earliblue, and it belongs to the northern highbush cultivar group [3]. In 1998, its clonal progeny was introduced from the United States for potted observation. Seedlings were propagated through greenwood cuttings and tissue culture techniques, and in 2001 they were planted in the small fruit experimental orchard of Jilin Agricultural University for field observation and preliminary selection. From 2005 to 2010, plot trials and cultivar comparison trials were conducted in the small fruit experimental orchard. From 2010 to 2014, regional trials and production trials were carried out in central and eastern Jilin Province, with the cultivar Northspring as the control cultivar. In addition, introduction trials or extension were also carried out in Dandong City and Shenyang City of Liaoning Province, Mudanjiang City of Heilongjiang Province, Rushan City of Shandong Province, Qinhuangdao City of Hebei Province, and other places. In 2016, it passed the approval of the Jilin Provincial Crop Variety Approval Committee and was named Bluetta.

2 Cultivar characteristics

2.1 Botanical characteristics

The plant posture of Bluetta is upright to semi-spreading, with moderate vigor. A 5-year-old tree is about 110-140 cm tall, with a crown diameter of 80-100 cm. New shoots are glabrous. Leaves are elliptical. The leaf underside is hairless, the leaf margin is sharply serrate or entire, and the leaf surface is smooth. The corolla is medium to large and cylindrical. During the bud stage, the corolla is pink, and after blooming the corolla color fades or disappears, appearing milky white. The corolla has ridges. The fruit cluster density is medium. The sepals are mostly upright. The fruit is oblate to round. The flesh is white. The average single fruit mass is 2.6 g, and the maximum is 3.5 g.

2.2 Growth and fruiting habits

The ability to produce basal shoots is moderate; a 4-year-old bush has 4-7 basal shoots. The flower-forming ability is strong, with 4-8 flower buds on each fruiting branch, and the flower bud rate is 16.3%. Each fruit cluster sets 3-8 fruits, and the natural fruit-setting rate is above 90%. The soluble solids content of the fruit is 12.7%, soluble sugar 9.65%, organic acid 1.22%, and vitamin C content per 100 g fresh fruit is 4.5 mg. The fruit scar is moist, and the bloom is medium-thick. The fruit texture is firm, the flesh is fine, the aroma is strong, and it is sweet and sour and palatable, with superior quality.

The results of many years of observation in the Changchun area show that it blooms in mid-to-late May. The fruit begins to color in late June, and 10% ripens around July 7, with the harvest period lasting 15-20 days. It takes about 50 days from flowering to fruit ripening, making it a very early-maturing cultivar. Leaf buds sprout at the same time as flower buds (May 1) or slightly later. New shoots stop growing from mid-June to early July, and then undergo secondary growth. Generally, new shoots have 1-3 growth flushes per year. Growth stops in late September, and leaf fall begins after mid-October.

The plot trial results show that in the 5th year after planting, the yield per 666.7 sq m was 477.7 kg. The average yield from the 3rd to 5th years after planting increased by 11.5% compared with the control cultivar Northspring. The regional trial and production trial results show that the yields in the 3rd and 4th years after planting increased by 4.7% and 7.8%, respectively, compared with the control (Table 1). This indicates that the Bluetta cultivar has good early high yield and strong continuous fruiting ability.

Table 1 Yield of Bluetta in regional trials and production trials

Note: 2-year-old seedlings were planted in 2011, with a plant spacing of 1 m x 2.5 m.

3 Pests, diseases, and climatic adaptability

Many years of field investigation in the Changchun area found no serious disease occurrence in Bluetta. There were occasionally slight damages by slug moths, scarab beetles, stink bugs, and others. At the trial sites in Jilin Province, overwintering without burying soil for cold protection resulted in severe shoot shriveling and basically no yield. Safe overwintering can be achieved by burying soil for cold protection. In Rushan City, Shandong Province, Bluetta grows and fruits normally in the open field, and its ripening period is slightly earlier than the cultivars Earlyblue and Duke, usually beginning to ripen around June 10.

Bluetta has the characteristics of very early maturity, high quality, high yield, stable yield, and strong cold resistance. However, the fruit has poor storage and transport tolerance and a relatively short shelf life, making it more suitable for planting in agritourism picking orchards.

4 Key cultivation techniques

(1) Seedling propagation. Use the greenwood cutting method or tissue culture method to propagate one-year-old seedlings, and after 2-3 years of cultivation, develop them into robust nutrient-pot seedlings with well-developed root systems. (2) Site selection and soil preparation. Choose flat land or gently sloping mountainous land with sufficient water source, no water accumulation, high organic matter content, and suitable acidity and alkalinity for orchard establishment. Soil preparation must be done before planting. Soil with organic matter content greater than 5% and pH 4.5-5.5 acidic sandy loam is preferable. If the soil pH is greater than 5.5, sulfur powder should be used to adjust the acidity throughout the orchard in proportion one year before planting [3]. Generally, for every 100 sq m of sandy soil with pH greater than 5.5, 0.367 kg of sulfur powder (about 200 mesh) is needed to lower the pH by 0.1 pH unit, while loam soil requires 1.222 kg of sulfur powder. The sulfur powder must be mixed evenly with the soil in the 20 cm layer. If the soil organic matter content is less than 5%, organic materials such as mixed peat soil need to be added before planting to increase the organic matter content. (3) Planting. Most planting is done in spring during the budbreak period. The plant spacing is 1 m x 2 m or 1 m x 2.5 m. Depending on the situation, choose flat-land cultivation, ridge cultivation, or raised-bed cultivation. Avoid planting too shallow or too deep. After planting, water thoroughly in time. Continuously maintaining good soil moisture is the key to obtaining a good survival rate. (4) Soil management. Within an 80 cm wide planting strip, clean cultivation may be used, or a 10 cm thick layer of organic material (such as bark or sawdust) or horticultural ground fabric may be used as mulch. Between rows, grass growing, clean cultivation, or horticultural ground fabric coverage may be used. In areas using soil burial for cold protection, organic material mulching and grass growing are not recommended. In the year of planting, cover the ground under the trees with black plastic film to improve the survival rate of planting and prevent weeds. Before winter, the plastic film must be removed before burying soil for cold protection. (5) Fertilization. From budbreak to harvest, fertilization can be divided into 4 applications (about 3-4 weeks apart): budbreak stage, young fruit swelling stage after fruit set, pink fruit stage, and harvest stage. Fertilization through a drip irrigation system is recommended. Generally, balanced fertilization with a nitrogen-phosphorus-potassium ratio of 1:1:1 is used. Nitrogen fertilizer should mainly be ammonium nitrogen. Chlorine-containing fertilizers should be avoided. Optional fertilizers include ammonium sulfate, potassium sulfate, diammonium phosphate, urea, and others. The annual fertilizer amount and fertilizer types need to be determined according to tree growth and fruiting, soil fertility status, and soil pH. (6) Irrigation. During the growing season, irrigation should be done in a timely manner according to soil moisture conditions. Drip irrigation is best. Pond water and reservoir water are preferable as water sources. [Jishan Huayao] Irrigate with freezing water before the soil freezes. (7) Pruning. Winter pruning is the main method, completed before spring budbreak. In areas using soil burial for cold protection, pruning should be carried out immediately after removing the soil. After planting, immediately thin out weak slender branches and cut back thick strong basal shoots. Nutrient-pot seedlings that have been planted may retain appropriately more branches. Bare-root seedlings (or transplanted large trees) must be heavily pruned. In the first two years after planting, flower buds should be thinned out, focusing mainly on building the tree structure. In the 3rd year, it enters the economic fruiting period. For mature trees, cultivate 2-3-year-old branch groups with strong fruiting ability, and promptly retract or thin out branch groups older than 5 years. Keep 4-6 perennial branches and 4-6 current-year basal shoots per bush, and promptly thin out weak slender branches, diseased and pest-infested branches, and dead branches. Appropriately control the number of flower buds on bushes at peak fruiting to prevent premature aging. (8) Cold protection. In most areas of Liaoning, Jilin, Heilongjiang, Hebei, and other provinces, it is necessary to irrigate with freezing water before the soil freezes, then press the bush down in one direction along the row and bury it with soil, with complete coverage as the standard. Remove all cold-protection soil before spring budbreak. Avoid using too much force and causing branches to break.