Applying the principles and methods of fruit tree breeding, it is a science and technology to study the genetic variation of plum and to breed new varieties of plum. There are about 30 horticultural species of plum in the world, among which the Chinese plum (Prunus salicina Lindl.) and the European plum (P. domestica L.) have the greatest economic value, which can be eaten freshly or canned, and in particular have great potential for drying. Cultivating new varieties of plum can improve the yield, quality and resistance of plum, and enhance its food value and economic benefits.

Brief history of development

Before and after 1860, the United States Terry (H.A. Terry) began to Lee's breeding work, breeding many excellent varieties. 1884, the United States famous fruit breeder Burbank (L. Burbank) from Japan to introduce the Chinese plum seedling, which selected the Burbank, Abundan-ce and Satsurna varieties. Satsurna varieties. Subsequently, he also crossed Chinese plums with other species of plums to produce the Santa Rosa variety, which is a mixture of Chinese plums, apricot plums (P...simonii Carr.) and American plums (P. amer-icana Marsh.), and for a long time was one of the major cultivars in the U.S. that was resistant to storage and transportation. At the same time, the Soviet Union, Michurin (И.В.Мичурин) also successively developed new varieties of Kozlov black plum and sweet prickly plum. By 1930, more than 10 states in the United States alone were engaged in plum breeding research. So far, the world to carry out plum breeding countries are the United States, Canada, Britain, France, Spain, Italy, Germany, South Africa, Sweden, Bulgaria, Yugoslavia, the Soviet Union, Hungary, Romania and Pakistan and more than 10 countries. China's plum breeding started late, began in the 1950s, Heilongjiang, Jilin and Xinjiang provinces (regions), a few research units carried out the work.

Breeding goals

Varies by country and region. In the same United States, Washington State requires the breeding of early-maturing varieties with very few physiological diseases; New York State is interested in varieties with improved resistance, improved quality, stable yields, and the ability to self-flowering and fruiting, and Georgia's goal is to breed varieties that can adapt to the southeastern U.S. cultivation conditions, and to different ripening periods. In France, the main objective is to produce a number of European plum varieties with a range of ripening stages suitable for drying and fresh eating. In Sweden, the goal of plum breeding is to produce cold-resistant, early-maturing fresh varieties. Central European countries and the USSR, to breed fresh, dried and used to make brandy wine of the European plum is the main focus, the requirements of the breeding of fruit traits better, more resistant to disease and cold resistance varieties. China, on the other hand, requires the breeding of cold-resistant Chinese plum varieties with large fruit size, good quality, and the ability to adapt to the natural conditions of Heilongjiang, Jilin, Xinjiang and other places.

Breeding pathways

Lee breeding pathways are: ① bud variation selection. It is an effective method to obtain new varieties. The United States Casselman and Late Santa Rosa is the Department of Santa Rosa from the bud varieties selected. ② Raw seed selection. Burbank is one of the early breeding methods. 1950s, China also utilized this method to breed new varieties such as Yuejin 6, Kueifeng, Kueiguan, Suileng red, Suileng 3, northern 2. ③ Hybridization breeding. Is the main method of Li breeding, through hybridization methods to breed many varieties, and the United States most. Among the famous ones are New York State Agricultural Experiment Station with Italian plum × Hall breeding Iroquois and Mo-hawka: Albion × Italian plum breeding Oneida, California Reynolds Experiment Station breeding there are three Chinese plum varieties Frontier, Friar and Queen Rosa, has been popularized in California. F. Anderson, a private breeder in the state, has bred one early Chinese plum (Red Beauty) that has been developed locally. Other Chinese plum varieties named for production are Amazon, Andys Pride, Ebony, Angeleno, Bee-Gee, and Black Queen. Also bred through crossbreeding are three European plum varieties bred in Canada in 1967: Valor, Verity and Vision. In addition, more than 20 European and Chinese plum varieties have been bred in the USSR and Romania, respectively, and China has bred a superior line of Chinese plums, Changchun 79-2-17.

Parental Selection

As a parent, there should be strong transmission ability It is desirable to select parents that are generally similar in terms of fruit ripeness, flesh hardness, fruit flavor and other traits. Chromosome ploidy varies among the species utilized as parents. The European plum and P. insi-titia L. are hexaploid (2n = 6x = 48); the blackthorn plum (P. spino-sa L.) is tetraploid (2n = 4x = 32); and the Chinese plum, the cherry plum (P. Cerasifera Ehrh.), the American plum, and many other species are diploid (2n = 2x = 16). Interspecific hybridization can often be successful when two parents have the same ploidy. If the two have different ploidy, after crossing, few seeds are produced, although fruit may be formed. E.J. Olden (1965) has cross-pollinated multiple combinations with many parents of different ploidy. He suggested that regardless of the ploidy of the parents, the success or failure of the crosses depended on whether or not a variety with a shorter pistil than the parent was used as the female. For example, in a forward and backcross with Primrose x Canada plum (P. nigra Ait.), fruiting was only possible when Primrose with a shorter pistil was used as the parent. Alden also found that hybridization between Prickly Plum and most diploids can be affinitive. In contrast, when crosses between diploid and hexaploid species were made with the diploid species as the mother, the percentage of fruit set was much higher than with the hexaploid species as the mother, but the viability of the seeds was low in both cases. When hexaploid European plums were used to cross diploid Chinese plums, the crosses were usually sterile. However, W. H. Griggs (1953) pointed out that Tragedy varieties belonging to the European plum were good pollinators of Chinese plums, but these Chinese plum varieties did not bear fruit when used to pollinate Tragedy. All these show that the different ploidy of Li is very important for the selection of parents, and must be highly valued, otherwise it will lead to pollination failure. In order to select pollination affinity of the parents, Flory (Flory), 1947 has been through the test, proposed a suitable for the southwestern United States when hybridization, different systems of varieties of the best pollination combination list: ① jam plum (P. hortu-lana Bailey.). Pollinated varieties are other varieties of the system or goose plum (P. munsoniana Wightet Hedr.); ② garden goose plum. Pollinators are varieties of the horticultural plum or Chinese plum system; (iii) Chinese plum. Pollinated varieties are most diploid species; ④ Asian plum (P. asiatica). Pollinated varieties are hybrids of narrow-leaved plum (P. angustifolia Marsh.) and goose plum systems in Native American species, and most varieties of the Chinese plum system.

Genetic studies

Fruit ripening stage of hybrid progeny of Chinese plum is a quantitative inheritance. The ripening period of the progeny is closely related to the average ripening period of the two parents, and not so much to the specific ripening period of one parent, and fruit size is also quantitatively inherited. Both parents with large fruits have progeny whose average fruit size is smaller than that of both parents. Fruit shape is controlled by multiple pairs of genes. These multiple pairs of genes are either dominant for round shape or dominant for ovoid shape. Yellow pericarp is a single gene and black, red, purple and ochre are recessive; the inheritance of these pericarp colors is quantitative. In flesh color, red is dominant over yellow and is a single gene. The intensity of red color is controlled by a complex gene. The off-nucleus trait appears to be a recessive. From progeny with both parents having sticky kernels, sometimes free kernels were found, but the maturity of the fruit and the softness or hardness of the flesh influenced the stickiness of the kernels. The fruit shape of the hybrid progeny of the European plum was dominant for broad oval over round. Fruit skin color was recessive for yellow versus red, purple, black, and ochre. Intense fruit powder was dominant over light fruit powder. Free kernel was recessive to sticky kernel. Openness of the tree is recessive; branching with hairy versus nearly hairless is dominant; hairy leaves and shorter stamens are dominant.