Scientific name: walnut, also known as walnut, peach and half a year. Juglandaceae, Juglans (about 18 species in this genus, distributed in north temperate zone. There are 4 species in China, 1 variety).

Form and use

Deciduous trees, up to 30 meters, DBH 1 meter. The bark is grayish white to dark gray. Branchlets glabrous; There is a flaky pith. Odd pinnate compound leaves, leaflets entire or nearly entire. The stigma of the female flower is yellow-green, and the drupe is nearly spherical. The drupe has two longitudinal ridges and the apex is blunt. The flowering period is from April to May, and the fruit ripens in September-165438+1October.

Seed kernel is used for food and medicine, with an oil content of 60%, and its oil is an excellent edible oil. Tannin can be extracted from bark and pulp. This kind of core can be used to make activated carbon. Leaves can kill insects. The wood is tough, the texture is beautiful, the heartwood is purplish brown, and the sapwood is reddish brown, which is collision-resistant. It is an excellent material for military industry, high-grade furniture, craft carving and so on. With deep roots and luxuriant leaves, the tree is magnificent, and it is also a good tree species for urban and rural greening.

(Hong Tao)

Geographical distribution and biological characteristics

There is a natural walnut forest at the northern foot of Tianshan Mountain in Xinjiang, China. Iran's Caspian Sea is also naturally distributed, extending westward to the Mediterranean region of the Balkans, eastward to the Caucasus and Central Asia of the Soviet Union, and southeast to the Himalayas. Since Zhang Qian sent an envoy to the Western Regions to plant walnuts in the Western Han Dynasty, the planting area of walnuts ranks first in the world. Walnuts are almost distributed in the range of 30 ~ 40 north latitude from north to southern Liaoning and south to northern Guangxi. Especially in the middle and lower reaches of the Yellow River and southwest China, it is the main producing area of walnuts. The vertical distribution of Juglans regia in North China is 500 ~ 1000 meters above sea level; Yunnan, Guizhou and Sichuan1300 ~ 2000m; Tibet1500 ~ 4030m. The distribution boundary is mainly limited by temperature, which is roughly consistent with the average monthly temperature of 1 0℃ in China, and the vertical distribution increases obviously in the southwest of low latitude.

Walnut is a broad-leaved tree species in warm temperate zone. Different geographical ecotypes have different requirements for climate. Juglans regia in northern China and Carpathian Juglans regia in eastern Europe are cold-tolerant, and can be cultivated in areas where the annual average temperature is 9 ~ 65438 04℃ and the growth period is about 200 days, and the dormancy period can withstand the low temperature of -37℃. China Yangbi Walnut and Mediterranean Walnut have poor cold resistance and can only grow in the north subtropical zone. The annual average temperature is 1 1 ~ 18℃, and the growing period is about 250 days. Walnut trees are extremely sensitive to late freezing injury, and flower buds and buds are vulnerable to freezing injury. Walnut root system is not tolerant to waterlogging, so it is not suitable for planting in areas with frequent waterlogging and high groundwater level. Walnut likes deep and loose neutral weak alkaline soil with pH above 6. It grows well on calcareous soil and carbonate brown soil with a depth of more than 2 meters; Under irrigation conditions, walnuts can also be cultivated when the soil depth is only 1 m; Walnut trees growing on acidic soil bear few fruits and are prone to illness. Walnut is a positive tree species, and both young and adult trees need sufficient light. Under shading conditions, the flower bud differentiation rate and fruit setting rate decreased due to the increase of carbon compounds and the decrease of nitrogen in photosynthetic products. Walnut trees are tall and long-lived, and 400-500-year-old trees can still bear fruit normally.

type

The objectives of walnut variety improvement are: ① high yield: mainly improve the related genetic traits that affect the yield, namely, the number of lateral flower buds, the number of female flowers per fruit order, fruit setting rate, single fruit weight and kernel weight; ② Nut quality: including nut size, shell thickness and kernel yield, kernel fullness and plumpness, kernel color and flavor, etc. ③ Resistance; Refers to the resistance of trees to cold damage (especially frost damage in the later period) and heat damage (sunburn of fruit trees, discoloration of nucleolus when heated, etc.). ), pests and diseases (brown spot, root rot, canker, etc. ) and soil salt damage. Since 1970s, with the popularization of grafting propagation method, a number of excellent clones have been provided, some of which have developed into varieties.

Walnut tree is a cross-pollinated tree species, and the heritability of each seed is different. There are more than 200 million walnut seedlings in China, which are very different, forming rich and colorful walnut germplasm resources. The important excellent seedling varieties are: ① Early fruiting walnut in Xinjiang: also known as walnut every other year. Originated in Aksu and other places in Xinjiang. After sowing, it will bear fruit in 1 ~ 3 years, and it will enter the full fruit stage in about 6 years, and the yield per hectare can be more than 1500 kg. ② Shanxi Walnut: It is native to Fenyang, Xiaoyi and other places in Shanxi. It is characterized by strong tree vigor, disease resistance, high yield and good nucleolus quality. ③ Hebei big thin-skinned walnut: also known as Shimen walnut. Originated in Beijing, Tangshan and other places. It is characterized by vigorous trees, strong resistance, nuts and shells sold in the international market. ④ Paper Walnut: Originated from Aksu, Xinjiang. It is characterized in that the shell is as thin as paper, the kernel rate is over 70%, and the kernel is milky white. ⑤ Walnut with large fruit: It is native to Hotan, Xinjiang. The trees are lush and the nuts weigh more than 25 grams. ⑥ Ear walnut: One fruit sequence bears more than 4 fruits, with a maximum of 43. Scattered all over the country, especially in Wushi County, Xinjiang. Yangbi Walnut is native to Yunnan, Guizhou, Sichuan and Guangxi, adapted to subtropical climate and grafted and propagated. Peasant varieties include pickled walnuts, three strokes walnuts, large white shell walnuts and so on.

According to the breeding objectives, excellent individual plants can be selected from existing seedling trees or progeny trees obtained by artificial hybridization, and excellent varieties can be selected through clonal identification. In order to speed up the breeding cycle, young trees over 5 years old can be selected as rootstocks for high grafting identification. Artificial hybridization is carried out within species or between species. The male inflorescence with yellow flower picking medicine and the anther at the base of inflorescence has begun to loose pollen, which can be scattered in a dry place for one day and night, and each anther can loose pollen at most 1800. Pollen can only be preserved for 2 ~ 3 days at room temperature; At about 5℃, it can be stored for more than 1 month; Pollen can still germinate after sealed storage at -30℃ for one year. In controlled pollination, female flowers should be bagged when they first appear; Pollination can be carried out from the little red dot of stigma to the bifurcation of feathery stigma, which lasts about 3 days; When the stigma appears brown stripes, it is the last stage of fertilization. The chromosome number of all species of Juglans is 32, and seeds can generally be obtained by interspecific hybridization. Natural interspecific hybrids include Juglans mandshurica (Juglans mandshurica× Juglans mandshurica), Juglans mandshurica (Juglans mandshurica× Juglans mandshurica), Juglans mandshurica (Juglans mandshurica× Juglans nigra) and Juglans mandshurica (Juglans mandshurica). In the United States, black walnuts are crossed with walnuts to improve flavor and cultivate rootstocks with strong resistance. The Soviet Union chose Juglans mandshurica and Keppel Walnut as parents to enhance cold resistance.

Afforestation technology

Walnut is propagated mainly by sowing and grafting. Seedlings are generally used as rootstocks. Grafting propagation can maintain the excellent characteristics of varieties and is the main propagation method for establishing walnut orchards. (1) Seeding and propagation: The green peel turns yellow, which is a sign of walnut maturity, so it can be harvested without waiting for the green peel to crack. Spraying olives with 500 ~ 1000 ppm ethephon, fumigating for 3 ~ 7 days, peeling, drying and storing. Seeds have no physiological post-ripening process and can be directly soaked in water. After fully absorbing water, it can germinate in a warm place of about 20℃ and germinate in about two weeks. Soaking seeds with 0.05% gibberellin solution can accelerate seed germination. Each hectare needs about 1350 kg of seeds, and can be fertile 105 thousand plants. 1 ha walnut seedlings need to consume 60 kg of nitrogen, 52.5 kg of potassium, 60 kg of calcium and 3 kg of sodium. The annual fertilization amount of nursery land is about 225 kg, and the ratio of nitrogen, phosphorus and potassium is 2∶2∶ 1. ② Grafting: including branch grafting and bud grafting (see tree grafting). Branch transplantation should be combined, tongue joint, split joint, skin inserted tongue joint and so on. The interface can heal in about 15 days in a moisturizing matrix at about 28℃. Indoor grafting can be carried out during the whole dormant period, and outdoor grafting in spring should be carried out after the scion is refrigerated at-1 ~ 3℃ during the dormant period until the maximum outdoor temperature rises to about 25℃, and the rootstock seedlings have sprouted and spread their leaves. At this time, the bleeding is reduced and the temperature is high, which is beneficial to healing. Rootstock seedlings can also be drained 2 weeks in advance, or by cutting off roots and injuring roots to reduce bleeding; Otherwise, the wound overflows the joint and hinders the formation of callus. In order to keep the scion dry, it can be wrapped with wax seal or plastic cloth. Bud grafting can be carried out after the new buds are fully developed in the same year, so as to ensure that the new branches germinated after the grafted buds survive can fully grow and mature and safely overwinter. Because the petiole of walnut is large, square bud grafting is better. After the petiole falls off about 1 week, it needs to be tied again 1 time to ensure that the bud piece is always close to the rootstock, which is beneficial to healing. The fruit of walnut is pith-bent, which is not suitable for grafting scion. Therefore, it is necessary to cut the ear from the adult tree in the previous year to promote the basal bud to produce full and straight development branches. In areas where the demand for scions is large, it is necessary to establish a scion nursery with excellent varieties. Grafting usually uses this rootstock, the interface heals well, there is no black spot, and the growth rate of rootstock and ear is the same. In addition, there are Juglans mandshurica, Juglans mandshurica and Pterocarya stenoptera. It can also be used as rootstock to enhance the stress resistance of Juglans mandshurica and reduce the tree body. ③ Garden construction: Sunny slopes and semi-sunny slopes with deep soil layers and good drainage should be selected as gardens. Terraces should be built to ensure that the soil depth is above 1.5 meters. 90 ~ 225 plants can be planted per hectare, and 4500 plants per hectare is suitable for dense planting garden of early fruiting varieties. In order to maintain soil and water and not affect intercropping, cave-like soil preparation is generally used. In rocky mountainous areas, large caves should be filled with exotic soil and organic fertilizers. Deep lime should be applied to acid soil, and quicklime 100 square meter 1 ~ 5 kg should be applied. Young gardens can be intercropped with short crops or green manure. ④ Shaping and pruning: generally, it is mainly trunk-shaped, and it is divided into three layers above the height of 65,438+0.5m. Each layer has 2-3 backbone branches, and each backbone branch can also have 3 secondary backbone branches to form a semicircular crown. It can also be layered, so that the main branches are evenly arranged on the trunk and keep a certain length to form a tower-shaped crown, which is suitable for close planting. The pruning of adult trees mainly focuses on controlling crown width and dimming. The branching ability of late-bearing walnut is low, and the top flower bud is the main fruit, so thinning is used to control crown expansion, and the extended branches are regularly retracted to the parts of 3-5-year-old branches. Walnut with early fruiting has strong branching ability and high proportion of lateral flower buds, which can be chopped mainly. According to the nutritional status of the tree, cut the chopped branches to 1/3 ~ 1/2 of the medium-long fruit branches to promote the mixed buds at the base of the fruit branches to germinate suitable and robust new fruit branches. Pruning can be done after defoliation, and bleeding is easy to occur at other times, but no significant effect of bleeding on growth and results has been found. Spring pruning can start about two months after germination. Pruning in spring will weaken the tree, but the wound will heal quickly. ⑤ Fertilization and irrigation: Applying organic fertilizer year by year in walnut orchard is an important measure to improve soil and ensure the supply of trace elements. When the amount of organic fertilizer is insufficient, inorganic fertilizer can be supplemented. According to the tree size, each fruit tree can be applied with chemical fertilizer1~1kg, and the ratio of nitrogen, phosphorus and potassium is 2∶ 1∶ 1. When magnesium, iron, copper, manganese, zinc and other elements in the soil are deficient or in a state that they cannot be absorbed and utilized, walnuts are characterized by element deficiency. In the walnut orchard suffering from chlorosis, 6% iron solution can be applied around the roots at the end of winter, which can maintain the efficacy for two years. When walnut lacks copper, the leaves turn yellow, the leaves fall early, and black spots appear on the branchlets and die. In spring, Bordeaux mixture can be sprayed or copper sulfate can be applied to the soil to prevent copper deficiency. When walnuts are deficient in zinc, "lobular disease" will occur. In severe cases, all the leaves become smaller and light green. Zinc nails can be nailed to tree trunks or twigs, which can take effect in time. Dig a ditch with a depth of 10cm from the trunk 1m, and apply 6 kg of zinc sulfate (small trees 1kg). Although walnut can grow and bear fruit without irrigation in areas with annual rainfall above 600 mm, due to the spring drought in northern China, if it can be irrigated 1 ~ 2 times two weeks after flowering, the fruit setting rate and fruit volume can be improved. Lack of water in July and August will affect the fullness of nucleolus; Irrigation 1 time in late September can promote lignification of branches and enhance cold resistance.

The main pests and diseases are anthracnose, Armillaria mellea root rot, walnut black spot, walnut dead branch, walnut limb moth, walnut giant elephant, walnut horizontal ditch elephant, straw sandals inchworm, beetle, walnut leaf moth, walnut caterpillar, thorn moth, longicorn beetle, weevil and scarab.

(Xi Ke Sheng)