Utilization and development trend analysis of Vaccinium of America in blueberry breeding

Abstract: As the core type of functional small berries, blueberries are well received by the market due to their unique taste, rich nutrition, and high health values. Now it has formed a global industrial cluster. The development of blueberry cultivars is originated from the United States, and its breeding process is related to the development and utilization of the Vaccinium resources in America. At present, there are about 150 species of Vaccinium in America, and more than 400 new blueberry cultivars have been devel- oped from the resources. However, due to the large factors of artificial directional selection in the pro- cess of blueberry breeding, the genetic basis of the selected cultivars was gradually narrowed, and the ability to resist biotic or abiotic stress was gradually reduced. The wild Vaccinium have a wide variety of resources, and they have accumulated a large number of high-quality trait genes under the conditions of long-term survival competition and natural selection. They are important breeding materials for the improvement of blueberry cultivars. This paper introduced the classification, distribution, and biologi- cal characteristics of Vaccinium resources in America, and the strategy and procedures for breeding new blueberry cultivars using Vaccinium resources in America. Based on the analysis of the genetic back-ground of the currently developed blueberry cultivars, it was found that V. corymbosum, V. angustifoli- um, V. darrowii and V. ashei were the main gene sources of blueberry cultivars. The development and utilization of V. constablaei, V. elliottii, V. myrtilloides, V. pallidum and V. tenellum further provided ex- cellent trait genes for the innovation of blueberry cultivars. Among them, the genetic background of the northern highbush blueberry cultivars mainly included the genes from V. corymbosum, V. angustifolium, V. darrowii, V. ashei, V. constablaei and V. tenellum. V. corymbosum and V. angustifolium constituted the main gene source of northern highbush blueberries, while V. ashei, V. darrowii, V. constablaei and V. tenellum constituted the secondary gene pool. The genetic background of southern highbush blueberry cultivars was more complicated, mainly including V. corymbosum, V. darrowii, V. ashei, V. angustifoli- um, V. constablaei, V. tenellum and V. elliottii. The average genetic contribution of V. corymbosum andV. darrowii was relatively large, followed by V. ashei and V. angustifolium, V. constablaei, V. tenellumand V. elliotti. Some cultivars also contained other Vaccinium genes such as diploid V. corymbosum, V. myrtilloides and V. myrsinites. The half highbush blueberry cultivars mainly contained V. angustifoliumand V. corymbosum genes, and some cultivars also contained V. pallidum and V. myrsinites. Rabbiteye blueberry mainly contained V. ashei and V. constablaei genes. The improvement of most lowbush blue- berry cultivars was limited to the excellent wild hybrids selected from V. angustifolium population. On- ly a few lowbush blueberry cultivars contained V. boreale, V. myrtilloides, V. corymbosum and V. consta- blaei. Finally, this paper analyzed the development and utilization trend of wild Vaccinium resources in American based on the current blueberry breeding goals. In summary: 1) Southern highbush blueberry cultivars had the largest number of developments, accounting for more than 50% of the total number of blueberry cultivars that had been announced. Cultivating high-quality southern highbush blueberry culti- vars is one of the current hot spots in blueberry breeding. The genes of V. darrowii, V. ashei, V. elliottiiand V. tenellum grown in the south of United States, with the low chilling requirement characteristics, are being incorporated into highbush blueberries to breed new blueberryvarietiess with early-ripening, large fruit, good flavor, strong adaptability, ith low or very low chilling requirement. 2) V. angustifoli- um, V. constablaei with cold-tolerance, and V. darrowii, V. ashei with strong cold-resistance are being used to broaden the genetic base of the northern highbush blueberry, and breed new blueberry cultivars with early-ripening, large fruit, good firmness, and cold resistance. 3) In recent years, the number of rab- biteye blueberry cultivars had been declining, mainly due to their large seeds and poor taste. The resent research suggested that 25% V. constablaei, 25% southern hexaploid V. corymbosum, and 50% V. asheishould be important combinations of the rabbiteye blueberries in the future, which would be helpful for broading the genetic basis of rabbiteye blueberries and breed new blueberry cultivars with late flower- ing, early ripening and good fruit quality. 4) Due to the limited planting area and commercial value of half highbush blueberries and lowbush blueberries, the number of new blueberry cultivars currently selected from them was the least, and breeding research and development were blocked. Therefore, collection and evaluation of wild Vaccinium resources, and exploration of the potential excellent traits of wildVaccinium is of great significance for the development of high-quality new blueberry cultivars with strong stress resistance and wide adaptability. This paper would provide an important reference for the development and utilization of wild Vaccinium germplasm resources in China.