How to conduct cross breeding?

The method of mating or combining fruit tree species or varieties with different genotypes to grow into hybrids and obtain new varieties through cultivation and selection. Cross breeding is the main way to cultivate new varieties and the most important method in modern breeding. Because of gene recombination caused by hybridization, offspring will have excellent trait genotypes controlled by parents, which will produce additive effects. By using some gene interactions, new individuals with super-parents will be formed, which provides a material basis for breeding and selection. The hybrid progeny population obtains excellent individual plants through the steps of cultivation, identification and selection, and then forms new varieties through asexual propagation.

British horticulturist T.A. Knight (1759 ~ 1838) began to cross-breed apple, pear, peach, plum, cherry, strawberry and other fruit trees after discovering the genetic influence of plant sex and male parent on their offspring, which made the breeding of fruit tree varieties develop from only using natural variation to artificially creating variation. Later, Darwin, burbank and michurin made extensive use of ecological geography, taxonomic distance and wild resources in the selection of hybrid parents. It has left valuable experience in the pre-selection of hybrids and the accumulation of selection effects for several consecutive sexual generations. Cross breeding in China began in the early 1950s and developed rapidly in the 1960s. At present, many units in China have carried out cross breeding of fruit trees, especially apples, pears, peaches and grapes, mainly aiming at high yield and high quality. Breeding new apple varieties such as Liaofu, Rose Red, Shengli and Qinguan; New pear varieties such as Zaosu, Jinfeng, Huanghua and Jinsu; New peach varieties such as Jingyu, Yuhualu and Chunlei; New grape varieties such as Beichun, Gongchun 1 and Zaohong have been popularized and applied in production. In addition to breeding new varieties, cross breeding technology and theoretical research have also made progress, such as the investigation, preservation and utilization of fruit tree variety resources in China. This paper studies the genetic law of different fruit tree characters, hybrid cultivation conditions and techniques, character identification and pre-selection, young development and control. It is more in-depth than other breeding methods in improving breeding technology and establishing breeding system.

Cross breeding can be divided into sexual cross breeding and asexual cross breeding according to its nature. In sexual hybridization breeding, it can be divided into interspecific hybridization and distant hybridization according to the distance of genetic relationship. General cross breeding refers to cross breeding among varieties. According to the different requirements of breeding, simple hybridization, backcross and multiple hybridization can be used (see sexual hybridization).

Determine the objectives of cross breeding and make breeding plans.

On the one hand, we should set our goals according to the needs of national economic development, such as cultivating canned peaches with yellow meat to meet the needs of China's foreign trade and cultivating large fruit and disease-resistant grapes to meet the needs of fresh food in the south; On the other hand, according to the problems of local fruit tree varieties, such as cold areas in the north, it is impossible to cultivate large apples with good quality, and the breeding goal can be to cultivate medium-sized apples with strong cold resistance and good quality. After the breeding goal is determined, a detailed plan to achieve the goal should be made. According to different goals and requirements, the length of the plan is different. Some people should not only consider 1 generation, but also consider the second and third generations and choose different hybridization methods. Each generation has to go through the process of parent selection, hybrid method design, hybrid cultivation and identification selection.

Parental Selection and Matching in Hybrid Breeding

Mainly consider the genes whose parents should have important target traits, and select traits with high breeding value. Considering the complementary genes of excellent characters between parents, parents with high combining ability which are far away in ecological geography are selected as parents for combination (see parental selection).

Hybridization method

Before hybridization, be familiar with flowering habits and flower organ structure in order to determine the time of pollen collection and pollination. Emasculation and pollination methods. It is necessary to know whether cleistogamy phenomenon exists in self-fertile varieties. For the type of male parent whose flowering period is later than that of female parent, the pollen of male parent can be stored for pollination every other year, or the branches of male parent with flower buds can be collected, put into bottles in advance, covered with plastic film, potted in greenhouse, or treated at low temperature at the end of last year to promote the early flowering of male parent through dormancy. Delayed pruning, early spring irrigation, canopy shading or hormone treatment can also be used to delay the flowering of mother trees, so as to adjust the pollination period and make parents meet at this flowering period.

Before pollination, hybridization tools should be prepared, including castration tools, powder storage bottles, pollinators, 70% alcohol, isolation bags and labels, binding materials, etc. Collect the well-developed buds that the male parent will open, pick the anthers indoors, dry them at room temperature, collect them in small bottles after the anthers crack and the pollen is scattered, label them, indicate the varieties, and immediately put them in a dryer for preservation. Pollen of apples, pears and peaches can be stored for 2 ~ 3 weeks under dry conditions at room temperature. Grapes and loquat can be preserved for 2 months; Persimmon pollen can only maintain its viability for 2 days under the same conditions. Pollen stored for a long time and sent from other places should be checked for viability before hybridization. The most commonly used method is to measure pollen germination ability. A culture medium was prepared with 1% agar and 5 ~ 10% sucrose. Pollen was sown on the culture medium to germinate at 25℃, and the germination was observed under a microscope. Those that have lost germination ability can no longer be used for pollination.

Hybridization should be carried out on the mother tree with strong growth and normal flowering and fruiting. The fully developed buds should be selected on the vigorous branches and kept at a certain distance from the pollinated flowers to ensure adequate nutrient supply in the future. Hybrid should choose sunny and windless weather. For bisexual flowers, in order to prevent self-pollination, they should be masculine before the anthers mature and crack. Pollination and bagging can be carried out immediately after emasculation; After bagging, label it, write down the hybrid parents and pollination date, and unpack it after 7 ~ 10 days. After pollination of each combination, the hybridization tool should be soaked in 70% alcohol to kill the pollen, so as not to bring the pollen of this combination to another combination.

Hybrid seed treatment and hybrid cultivation

The hybrid fruit should be harvested at an appropriate later stage so that the seeds can fully mature. After harvesting, put it in a cold place to ripen. The seeds of deciduous fruit trees have to undergo a period of low temperature stratification before sowing. In stratification treatment, usually 1 seed is mixed with 4-5 parts of wet river sand, evenly layered and placed in a box, and placed in a cool place at 2-4℃, and can be sown in about 2 months. It takes a period of childhood for hybrid seeds to germinate, blossom and bear fruit. In the early stage of seedling growth, measures such as strengthening fertilizer and water and light cutting were taken. Promote the rapid expansion of the crown and accelerate the accumulation of nutrients and other substances. In the later stage, measures such as controlling fertilizer and water, bending branches, twisting branches and spraying growth retardants were taken to control vegetative growth, promote its transformation to reproductive growth, and blossom and bear fruit early (see offspring cultivation).

Selection and identification of hybrids

In the process of hybrid cultivation, hybrid identification and selection are carried out. Before fruiting, botanical characteristics, resistance and physiological and biochemical characteristics can be directly or indirectly identified in the field, greenhouse or laboratory, and a large number of unqualified hybrid seedlings can be eliminated on this basis, thus saving land, manpower and material resources. In the fruiting period, the main economic and biological characters such as fruit were identified for 3 ~ 5 years in a row, and excellent individual plants were selected (see character identification), and then new varieties were selected through variety comparison test and regional test.