Cross breeding techniques of Walnut

Walnut is an important oil fruit tree. Walnut oil and content is generally 60%-75%, protein content of more than 15%, but also contains calcium, phosphorus, iron, vitamins and other nutrients. It is not only a nutritious food, but also has great medical effect. Walnut likes light, cold tolerance, strong drought resistance and disease resistance, adapts to a variety of soil growth, and does not require high environmental conditions. Walnut is especially suitable for barren hills and barren slopes. It is an ideal economic tree for returning farmland to forest. It is of great practical significance for the development of walnut industry to cultivate excellent tree species suitable for local growth, develop cross breeding, make walnut early fruiting and high yield, enhance growth potential, productivity and stress resistance, and improve economic benefits per unit area.

I. the structure and flowering habits of flowers

The male flower of the walnut is born at the apex of the previous year's branch, and the female flower is born at the top of the current year's branch. The male flower buds formed in the axils of leaves from April to May last year, with 1-2 small protuberances at first, mulberry-shaped in autumn, and flowering from April to May next year. Male inflorescences catkin-shaped, each inflorescence has 100cm 170 florets, each floret has 12cm 26 stamens, filaments short, anthers yellowish green, hypertrophy. Female flowers are clustered, each cluster is mostly 1-3, stigma 2-lobed, feathery, papillae above, ovary inferior.

Walnut is a monoecious, cross-pollinated tree species. However, the florescence is mostly different, and very few flowers bloom at the same time. The blooming dates of female flowers and male flowers on the same branch are generally 7-10 days apart.

II. Hybrid combinations and parent selection

The selection of hybrid combinations must be based on the purpose of hybridization. If high-yield varieties are cultivated, high-yield parents must be selected; if cold-tolerant varieties are cultivated, parents with high altitude and high latitudes should be selected. Generally speaking, the best parents are the fine individual plants that have been carefully selected. The economic characters, biological characters and resistance of fine individual plants should be understood comprehensively and systematically in order to meet the requirements of further cultivation of improved varieties. In order to enhance heterosis, different ecological types can also be used for hybridization.

In addition to intraspecific hybridization, walnut can also be crossed with different genera and species of the same family. Such as mixed pollination with the pollen of Juglans mandshurica and Carya cathayensis.

Whether excellent single plant or general fruiting tree is selected as hybrid parent, middle-aged plants with strong growth, no diseases and insect pests, large crown, branches and many female flowers should be selected. The middle-aged fruiting trees are well developed, have strong vitality, exuberant metabolism and full kernels after hybridization.

III. Hybrid technology

1. Pollen collection

Walnut pollen can be collected by the following two methods: one is that during the peak period of loose powder in male flowers, the pollen is shaken and dropped in the collector by climbing trees from 8 am to 2 pm. Another method is to collect the male inflorescences that will be blooming or blooming, put them in a dry place or in a dryer, crack and disperse the powder after losing water, collect and remove impurities and install them in the test tube, plug the test tube with cotton and store them in the dryer, preferably in the refrigerator.

two。 Bagging

Isolation generally requires bagging 3-5 days before the male flower is pollinated. The development of the female flower will be affected prematurely, and it is easy to mix with other pollen if it is too late. The best bagging material is parchment or transparent paper. The size of the bag is about 45cm long and 25cm wide. When bagging, first cut off the larger leaves in the lower part of the branches, and then cut off half of the young leaves close to the female flowers. Pad a small amount of cotton where the mouth of the bag meets the branches, and then tie it tightly with thread to prevent other pollen from invading.

3. Pollination

After bagging isolation, observe every day for timely pollination. Usually, the temperature and humidity in the bag are higher than those outside the bag, and the development period of the female flower is 1-2 days earlier than that outside the bag. The most suitable pollination period is 2-3 days after flowering. At this time, the walnut stigma has changed from turquoise to yellowish green, opening horizontally to both sides, shining and slime. Pollination takes place before 10:00 in the morning. When the temperature is high at noon, the mother tree spreads a lot of powder, which is easy to mix with other pollen, which affects the accuracy of hybridization.

When pollinating with a pollinator, cut a small hole in the upper part of the bag mouth and insert the pollinator nozzle to pollinate. When pollinating with a brush or cotton ball, you should first remove the bag or cut off the top of the bag and then pollinate. Fold the mouth of the bag several times after pollination and fasten or re-tie the bag with a paper clip. In order to increase the fruit setting rate, pollination should be repeated 2-3 times, that is, once a day or every other day.