Cross-breeding technology of walnut

Walnut is an important oil fruit tree. Walnut oil and its content is generally 60% to 75%, protein content of more than 15%, but also contains calcium, phosphorus, iron, vitamins and other nutrients. It is both nutritious food and great medical efficacy. The walnuts are hi light, cold-resistant, drought-resistant and disease-resistant. They adapt to a variety of soil growth and have low requirements for environmental conditions. They are particularly suitable for barren hills and slopes. They are the ideal economic forests for returning farmland to forests. It is of great practical significance for the development of the walnut industry to develop suitable tree species suitable for local growth, develop hybrid breeding, increase early growth of walnuts, increase growth potential, productivity and resistance, and increase the economic benefits per unit area.

1 Flower structure and flowering habits

The male flower of the walnut was planted at the tip of the branch of the previous year, and the female flower was born at the top of the original branch. In the spring of April to May last year, the male flower buds were already formed between the leaf buds, with 1 to 2 small protuberculosis at the beginning, and mulberry-like in autumn, and flowering loose powder from April to May in the following spring. Male inflorescences are soft and podlike, with 100 to 170 flowers in each inflorescence. Each floret has 12 to 26 stamens, short filaments, yellow-green anthers, and hypertrophy. Female flowers are clustered, with 1 to 3 per cluster, stigma 2-lobed, featherlike, with papillary protrusions, and ovary lower.

Walnut is a tree species with different sex and cross pollination. However, the flowering period is often inconsistent and there is very little opening during the same period. The opening dates of female flowers and male flowers on the same branch are generally separated by 7-10 days.

2 Hybrid combinations and parent selection

The selection of hybrid combinations must be based on the purpose of hybridization. If a high-yielding species is cultivated, a high-yield parent must be selected; if a cold-tolerant species is cultivated, parents that distribute high altitude and high latitudes should be selected. In general, the best of the parents is the well-chosen fine plant. A comprehensive and systematic understanding of the economic traits, biological characteristics, and resistance of good individuals should be made in order to meet the requirements for further training of improved varieties. In order to enhance heterosis, different ecological types can also be used for hybridization.

In addition to intraspecific hybrids, walnuts can also be crossed in different genera and species in the same family. For example, pollen mixed with walnut pods and shell pecans is used for pollination.

Regardless of the selection of a good single plant or a general result tree as the parent of the cross, the middle-aged plants should be grown with robust growth, no pests and diseases, large canopies, branches, and more female flowers. The middle-aged result tree grows well, has a strong life force, and has a strong metabolic effect.

3 Hybridization technology

3.1 Pollen collection

Walnut pollen can be collected in the following two ways: One is during the golden age of male flowers, from 8 to 9 o'clock in the morning to 2 or 3 o'clock in the afternoon, the tree shakes the pollen in the collector; the other method is to collect The open or open male inflorescence is placed in a dry place or in a desiccator to dry it. The anther is dehydrated and then cracked to loosen the powder. After being collected and removed, it is placed in a test tube. The test tube is stuffed with cotton and stored in a desiccator. Spare in the refrigerator.

3.2 Bagging

Segregation generally requires 3 to 5 days before male flocks to be bagged, prematurely affecting the development of female flowers and mixing with other pollen later in the day. The best choice for bagging materials is parchment paper or transparent paper. The size of the bag is 45 cm in length and 25 cm in width. When the bag is bagged, the larger leaves at the lower part of the branches are cut first, and then the young leaves near the female flowers are cut. A small amount of cotton should be placed between the mouth of the bag and the branches, and then tied tightly to prevent other pollen from invading.

3.3 Pollination

After bagging isolation, observe it every day to pollinate timely. Generally, the temperature and humidity in the bag are higher than those outside the bag, and the development period of the female flower is 1 to 2 days earlier than the bag. The most suitable pollination period is 2 to 3 days after flowering. At this time, the stigma of the walnut has changed from greenish green to yellowish green, spreading horizontally to both sides, shining and mucus. Pollination is conducted before 10 o'clock in the morning. At noon the temperature is high, and the mother tree is heavily pollinated and is prone to miscellaneous pollen, affecting the accuracy of hybridization.

When pollinating with a duster, a small mouth is cut in the upper part of the bag mouth and pollinator mouth is inserted to pollinate. When pollen is pollinated with a brush or cotton ball, the bag should be bagged or trimmed and then pollinated. After the pollination is completed, fold the folds of the bag and use a paper clip to tighten or reattach the bag. In order to increase the fruit setting rate, pollination should be repeated 2 or 3 times, ie, pollination once a day or every other day.

3.4 Management

About 3 to 5 days after pollination, the stigma is dry, and the ovary rapidly expands in about 10 days. Therefore, about 1 week after pollination, the bag can be removed to facilitate fruit growth and timely picking. After the hybrid seed is cultivated into seedlings, it is selected through strict seedling stage, and then asexual propagation methods such as bud grafting and shoot grafting are used to form different clones, and the quality thereof is confirmed before it can be extended to production.

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