The seed orchard has a large row spacing, especially in the early stage of garden construction, and the woodland is relatively bare. In order to promote the growth of mother trees, we must pay attention to soil management.
Improving the water and fertilizer conditions in the seed orchard is beneficial to the growth and development of trees, increasing seed yield and reducing the phenomenon of equal intervals between different years. Therefore, when the seed orchard enters the flowering and fruiting period, it consumes more nutrients, which sometimes affects the seed yield in the following year. In order to achieve the requirements of stable yield, high yield and high quality, reasonable fertilization must be carried out. Fertilization in seed orchard should adopt different fertilization methods and amounts according to different development stages.
At the beginning of the garden, due to the large spacing between plants, the woodland is fully exposed, and crops, medicinal materials, green manure and other medicinal materials can be intercropped. This can not only make full use of land to obtain benefits, but also further improve the fertility of forest land. At the same time, weeding, loosening soil and ridging are carried out 2 ~ 3 times a year, and the broadband width is increased year by year to promote the root system development of mother trees.
When the mother tree enters the flowering and fruiting stage, because it consumes a lot of nutrients, if it can't absorb enough nutrients from the soil, it will often obviously affect the differentiation of flower buds and the yield of fruit seeds. Rational fertilization is an effective way to solve nutrient supply. It is best for the fertilizer to have the characteristics of long validity period, great effect, low loss rate, low price and sufficient source. Generally, manure, compost, human excrement and mineral fertilizer are better. Fertilization methods can be used to dig pits, open annular ditches or longitudinal ditches.
Fertilization in seed orchard should adopt different fertilization methods and amounts according to different development stages, from planting to harvesting. For example, when young, fertilization should be conducive to the formation of dental crowns; Fruits are vigorous at maturity, and the harvest is large, so it is necessary to supplement the nutrients consumed by flowering and fruiting every year; In old age, trees begin to decline, so fertilization should be combined with pruning to prevent the decline of seed yield and quality.
Rational fertilization not only varies with the development stage of tree species and plants, but also should consider the nutritional status of soil in seed orchard. Therefore, it is difficult to put forward a reasonable fertilization scheme without soil analysis, nutritional diagnosis and comparative test.
We must pay attention to the water condition of the seed orchard, which will not threaten the growth and development of the seed orchard in general years, but occasionally needs irrigation in severe drought years; Water accumulation should be eliminated in years with excessive precipitation.
Fertilization combined with irrigation has good effect.
Intertillage can loosen the soil, improve the permeability of water in the soil, increase water retention, and thus improve the growth conditions, and the effect is the best in midsummer. Pollen management in seed orchard includes two aspects: on the one hand, it is to prevent pollen from flying into the garden outside the seed orchard and causing pollution; On the other hand, clones or families in the garden can fully pollinate each other, expand the genetic basis of seeds and reduce self-pollination. These two aspects are related to the propagation distance, flowering period, pollen yield and pollination characteristics of pollen, so it is necessary to study the flowering and fruiting habits of pollen.
1, pollen spread
Pollen transmission is related to tree species, pollen structure, pollen concentration, topography, wind speed, humidity and other factors.
Although the pollen of most wind-borne trees can fly far away, with the increase of distance, the pollen density decreases and the probability of fertilization decreases obviously. According to Wrignt's research, the pollen source concentration range of each tree species is110, which is roughly as follows: Fraxinus mandshurica 18m, spruce 38 ~ 90m, Pinus densiflora over 60m and Ulmus pumila 660m. It has been reported in Japan that the pollination rate of Cryptomeria japonica is below 20% when the crown is closed, and the distance is more than 9 m, which is invalid. The seed orchard should keep an effective distance from the inferior pollen source, and carry out auxiliary pollination on the trees with short effective distance of pollen in the orchard, and extend it to the whole orchard to achieve random mating.
The vertical distribution of pollen in seed orchard is also different. When the average tree height in the seed orchard is greater than 4m, before canopy closure, if the pollen reception at the height of 2 m is 100%, the pollen reception at the heights of 4 m, 6 m and 8 m are 185%, 190% and 230% respectively, and the pollen at the lower part of canopy closure is/kloc-respectively.
The receiving trends of plant crowns in different directions in gardens are different. The pollen reception of 4m and 8m crowns is basically consistent with the wind frequency, while the reception of 2m is affected by the wind frequency and the surrounding male cones. The maximum reception often occurs in the downwind direction of a large number of male cones in the range of 15m.
This characteristic of pollen distribution in Pinus tabulaeformis seed orchard is analyzed, which is related to the structural characteristics of pine pollen and the higher wind speed in the upper layer of canopy than in the lower layer. Before the canopy was formed, with the increase of temperature, the pollen in the lower layer was carried to the upper layer by airflow. Therefore, the seed orchard set on the slope is conducive to the spread of pollen.
2. Clonal flowering period
Different clones often have different flowering periods, which can be generally divided into early, middle and late. Because the propagation materials come from different regions, the garden was built in the early stage, and the flowering habits of each clone were not known, so the uneven flowering period was inevitable. In this way, the flowering period does not match or only 1/2 or 1/3 clones can pollinate each other, which reduces the effective number of clones in the seed orchard. For example, the observation of 5 1 clone in Liaoning Xingcheng Pinus tabulaeformis seed orchard shows that the flowering period can be roughly divided into three categories: early, early and late. I don't meet in the morning and evening.
3. Pollen yield
The pollen yield of each clone in the seed orchard will not be equal. It often happens that a few clones with high pollen yield monopolize the whole seed orchard. Especially in the early flowering period, the monopoly function is more prominent. The difference of pollen yield will inevitably affect pollination and fruiting, which makes the offspring of one parent or two parents in the seed orchard have a high proportion.
The probability of free mating between clones can be roughly equal only if the yield of male and female cones in seed orchard is similar and the flowering period is synchronous. The mating probability of different clones and individual plants is not equal, and random mating between clones in seed orchard can not be realized, which will make the outcrossing combination drop sharply. There are many research reports in this field. In loblolly pine seed orchard composed of 15 clones, 4 clones produced more than half of the seeds, and 20% clones produced nearly 56% of the seeds in slash pine seed orchard. In spruce seed orchard, 1/3 clone produced most male cones and female cones.
According to the observation of Pinus tabulaeformis seed orchard, there is a great difference in cone yield between male and female among different clones, even among different ramets of the same clone, and the phenomenon of pollen monopoly is very prominent. In 1982, the two clones with high yield of male cones accounted for 57% of the total flowers in Xingcheng seed orchard in Liaoning Province. Seven clones accounted for 92.4% of the total flowers; There are 28 clones that don't work, and this imbalance tends to ease with the increase of tree age, but it still exists in 199 1 year. 1 clone accounts for 1 1%, and the least clone accounts for only 0.07% of the total flowers, with a difference of/
4. Self-pollination
Although it is assumed that outcrossing seeds can be obtained through the arrangement and configuration of clones in seed orchards, in fact, there is always some degree of self-pollination in seed orchards (especially conifers), which leads to self-pollination of seeds, with the adverse consequences of flower decline. Miller—Starer research shows that the average self-pollination rate of Pinus densiflora seed orchard in Europe is 6%.
Observation of Pinus tabulaeformis seed orchards in Xingcheng, Liaoning Province and Lushi, Henan Province showed that when the pollen amount was 3kg/hm, the ovule abortion rate was 58.6%, and when the pollen amount increased to 7kg/hm, the abortion rate decreased to 43.65438 0%.
Self-recession has always been one of the problems that tree breeders have to avoid, because the wild population of trees often carries a large number of harmful recessive genes, and these genes will not cause harm in the case of random mating, because each tree is often pollinated by other trees without the same recessive genes, and harmful recessive genes cannot be expressed in hybrids. However, when self-pollination occurs, some individuals will become recessive homozygotes, that is, obvious self-pollination decline will occur.
First of all, seed setting is reduced and vitality is reduced. For example, self-pollination of Cryptomeria japonica, its seed yield is 30% and 20% lower than that of open pollination and artificial outcrossing, and its seed germination rate is correspondingly reduced by 140% and 270%. Secondly, the formation of empty or astringent seeds, harmful recessive genes may play a role in seed development, so that fertilized embryos die early in development. Third, poor adaptability and reduced growth. For example, the survival rate of self-pollinated progeny seedlings of Cryptomeria japonica is 20% and 83% lower than that of free pollination and artificial outcrossing, respectively. Compared with free pollination, the volume growth of self-pollinated progeny of Picea crassifolia decreased to 1 ~ 2 times when it was 6 1 year.
5. Pollen management measures
Because there are different pollen propagation distances, different pollen yields and inconsistent flowering periods in seed orchards, that is, self-pollination should be strengthened. Specific measures are as follows:
(1) Strictly select the garden site, and it is best to set the seed garden outside the natural distribution area of tree species, avoiding setting it in the concentrated distribution area or increasing the distance of isolation belt.
(2) Increase the area of seed orchard and control the shape of seed orchard. The number of clones should not be too small, and the flowering period of clones should be consistent, at least in the same community.
(3) Control the number of male and female flowers of each clone to be approximately the same, and cross between clones is enough.
(4) auxiliary pollination is adopted
Auxiliary pollination refers to artificial auxiliary pollination without castration and bagging. It can improve the seed yield, especially for small seed orchards or seed orchards at the initial stage of fruiting. Auxiliary pollination can supplement the deficiency of natural pollination and improve seed yield.
Timely auxiliary pollination is a simple and effective method to improve seed yield and genetic quality. When the pollen density in seed orchard is low, the seed yield can be significantly improved. When pollen supply is sufficient, auxiliary pollination can not improve seed yield, but can significantly improve genetic efficiency. Artificial pollination is an effective method to reduce empty seeds produced by self-pollination in seed orchards. In the suitable pollination period of female cones, it is of great significance to improve the yield and quality of seed orchards by using multi-strains, especially excellent clones that have been genetically determined.
The main functions of auxiliary pollination are as follows:
Improve seed yield. Small seed orchards or seed orchards are in the early stage of fruiting, and auxiliary pollination can supplement the shortage of natural pollination and improve seed yield.
Reduce the self-pollination range of seeds. Especially when the florescence of ramets of the same clone is the same.
Overcome the phenomenon of pollen quantity superiority of a few clones in seed orchard. The pollen of artificial pollination is equal to the mixed pollen of excellent parents, so it can overcome the dominant phenomenon of a few clonal pollen in seed orchard.
Expand the genetic basis and improve the genetic quality of offspring seeds. Through artificial pollination, the interference conditions of exogenous bad pollen can be minimized, pollen pollution can be reduced, and inferior seeds can be reduced. The key point of tree management is to prune trees artificially, to dwarf trees, to expand the fruit-bearing area, and to facilitate management operation and fruit picking. Thus, the work efficiency is improved and the seed production cost is reduced. Therefore, tree dwarfing has become an important measure for seed orchard management.
Adequate illumination is a necessary condition to ensure flowering and fruiting. At the same time, tall trees bring difficulties to seed collection and seed orchard management. As early as 1960s, foreign countries began to explore tree management in seed orchards. The tree species studied are Abies fargesii, Picea crassifolia, Pinus taeda, Pinus radiata, Pinus koraiensis and Larix kaempferi, and the pruning methods adopted are pruning, thinning and short cutting. The topping test of Picea crassifolia shows that topping is effective in promoting the yield of male and female cones and controlling their distribution. On the contrary, the topping advantage of loblolly pine is obvious, and the crown growth can not be effectively controlled after topping, and pruning will only reduce the yield. Topping of Taxodium distichum reduces the yield of female cones, but has little effect on male cones, and the effect of controlling tree height is not obvious.
Dwarfing and pruning experiments were also carried out on Pinus sylvestris var. mongolica. Pinus sylvestris var. mongolica, Pinus koraiensis, Larix gmelinii and Pinus tabulaeformis in China. Cut off the main tip of Korean pine to form a cup-shaped crown, which improves the seed setting rate by 40%. Short-term cutting of Larix principis-rupprechtii can significantly increase the flowering amount of branches, but the effect of topping to control high growth is not ideal. So far, there is no mature experience in the plastic pruning technology of seed orchard.
Eliminating inferior quality and thinning is one of the important measures to improve seed yield and genetic quality in primary seed orchards. By eliminating the bad and thinning, we can ensure that trees have enough light to meet the development of crown. Clones and families with poor genetic quality can be eliminated according to the measured data of offspring and the understanding of flowering and fruiting habits. If the flowering period cannot be reached, or the seed yield is extremely low, it can also be cut down as appropriate. Pest control is also one of the main contents of seed orchard management. In seed orchards, flowers, fruits and seeds are often harmed by pests and diseases. For example, in the seed orchard of Pinus tabulaeformis, the main pests that harm the annual cone of/kloc-0 are pine borer and gall midge; The main pests that harm 2-year-old cones are pine cone borer, red pine cone borer, pine cone borer and so on. The main pest that harms larch cones is larch flower fly. Pests and diseases in seed orchards will often have serious consequences if they are not prevented in time. According to the management experience of the Southern Pine Seed Orchard in the United States, more than 90% of the seed yield will suffer losses if no measures are taken to prevent diseases and insects. In Xingcheng Seed Orchard, Liaoning Province, after three years of follow-up investigation, about 90% of the total amount of spheroidization suffered from pests.
In order to control pests and diseases, it is necessary to study the occurrence law of pests and diseases, establish a forecasting system for pests and diseases, and take effective control measures. Biological control is the future development direction, but in today's production practice, chemical control is still the main one.