Breeding techniques of virus-free Container seedlings of improved Citrus varieties

Breeding techniques of virus-free Container seedlings of improved Citrus varieties

1 virus-free three-stage breeding system of improved citrus varieties

The virus-free three-stage breeding system of improved citrus varieties is the basis of virus-free seedling breeding (figure 1). The first level is the technical core, which makes the excellent variety resources at home and abroad virus-free, and constructs the preservation bank of virus-free improved varieties, the mother garden and the first-level ear-picking nursery; the second level is the second-level ear-picking nursery, which is an important link of propagation; the third level is the breeding nursery of improved varieties around the country. This system has complete functions, graded establishment and independent existence, which ensures the safety of materials in each link and has a three-stage magnifying effect on the speed of breeding and popularization. it has innovative progress in disease detection efficiency, seedling quality, guarantee mechanism, promotion mode and so on, and it is a model of citrus seedling breeding technology in China. At the same time, the implementation of the people's Republic of China national standard "Citrus grafted seedlings", the agricultural industry standard "Citrus virus-free seedlings breeding Standards" and "Citrus seedlings virus-free Technical specifications" and other standards and technical requirements.

Fig. 1 schematic diagram of virus-free three-stage breeding system of improved citrus varieties

2 breeding techniques of virus-free container seedlings of citrus

2.1 basic components

The breeding of citrus virus-free container seedlings requires several functional areas, such as virus-free seed preservation bank, virus-free maternal parent garden (exhibition garden), rootstock seed orchard, virus-free spike nursery, rootstock seedling propagation nursery and seedling breeding nursery, which is referred to as "one bank, two gardens and three nurseries". The specific requirements and functions are described below.

2.1.1 good mother trees or introduced materials in the field of virus-free improved varieties should be tested for diseases. The disease-free plants were planted and preserved in isolation in the net room, with 2 to 4 plants per variety, and the diseased plants were removed before entering the improved variety bank. Disease detection and detoxification included strains of citrus Huanglong disease pathogen (HLB), peeling virus-like virus (CEV), leaf fragmentation virus (CTLV), pomelo dwarf disease caused by decay virus (CTV) and sweet orange stem pitting disease, and Wenzhou mandarin wilt disease (SDV).

2.1.2 the virus-free maternal garden (exhibition garden) propagated 266 strains of virus-free materials from the improved variety preservation bank, and planted in the maternal garden according to the row spacing of 3 m × 4 m or 4 m × 5 m according to different varieties. The horticultural characters of each plant were investigated, analyzed and recorded. After showing the inherent horticultural characters, the mother tree was selected to provide virus-free scion and ear picking nursery was established. Pay attention to observe the symptoms of the disease, and use indicator plants or RTPCR to detect the susceptibility every 3 years.

2.1.3 rootstock seed orchards need to be established in order to ensure the purity, quantity and safety of rootstocks. According to the needs of cultivating seedlings, the variety and quantity of rootstocks were determined and planted in isolation, so as to avoid cross variation.

2.1.4 the scions and rootstocks of scion trees in virus-free spike nursery were all from virus-free mother orchard and rootstock seed orchard, and different varieties were closely planted in different regions. The time of scion collection is limited to 3 years after the plant is planted in the spike nursery.

2.1.5 A greenhouse with controllable temperature and humidity is generally used in the rootstock seedling breeding nursery, and the facilities, soil and seeds in the greenhouse should be sterilized.

2.1.6 Seedling breeding nursery is a place for virus-free container seedling breeding, which should be equipped with batching yard (equipment), production material stacking yard, seedling loading and unloading yard (tools), fertilization and irrigation system, etc. and set up new seedling breeding area, old seedling renewal area and so on.

The commonly used tools in each functional area shall be dedicated. Shears, knives, saws, etc., shall be washed with soap and disinfected with 1% sodium hypochlorite solution before each variety is operated. The staff went in and out of the garden and paid attention to disinfection. Strictly implement the system of entry and exit registration and safety quarantine of other personnel. In particular, it is reminded that in the Huanglong disease area, the above six functional areas need to be established in the net room of 40 mesh yarn (steel) mesh.

2.2 breeding techniques of virus-free container seedlings

The so-called citrus seedlings are grafted seedlings that meet the standards of GB/T5040-2003 "Citrus Seedling producing area Quarantine regulations" and GB/T9659-2008 "Citrus grafted seedlings". Citrus virus-free container seedlings refer to the seedlings cultivated in containers, which not only meet the requirements of the above two national standards, but also use citrus materials from "one bank, two gardens and three nurseries" and according to the requirements of virus-free management.

2.2.1 the procedure of rootstock seedling breeding is as follows: collecting seeds-seed storage (or young seeds sowing with sowing)-sowing formula soil preparation-sowing soil disinfection-seed disinfection-sowing-soil and seedling management after sowing.

The formula soil is a mixture of river sand, husk and peat with a volume ratio of 1 ∶ 1 ∶ 2. The soil is disinfected with chlorpromazine and other agents, and the seeds are disinfected with 0.4% potassium permanganate. Sowing immediately after disinfection, it is appropriate for each seed to occupy 9 square centimeters. From sowing to transplanting, the temperature shall not exceed 35 ℃, the soil water content shall not exceed 70%, 0.2% and 0.5% water and fertilizer shall be added every 7 to 10 days, and attention should be paid to the prevention of seedling diseases such as blight. The common ways of rootstock seedling cultivation are as follows (Fig. 2-Fig. 3).

Fig. 2 Seedling bed sowing

Fig. 3 seeder sowing

2.2.2 grafting seedling breeding transplant the rootstock seedlings in the rootstock breeding nursery into a seedling container, and when the thickness of the rootstock reaches 0.4 cm 0.5 cm from the ground (grafting site) (figure 4), the robust scions in the virus-free spike nursery were collected for grafting. Generally, cutting is used when the temperature is low, and small buds are used as far as possible when the temperature is high. After grafting, the seedlings grafted with ventral grafting in spring can promote the germination of ventral rootstock in summer and autumn, and the seedlings grafted with ventral grafting in autumn and winter can be cut to promote their development in the spring of the following year.

Fig. 4 rootstock seedlings to be grafted

After budding and before the first shoot self-cutting, the fungicide to prevent anthracnose was sprayed 3 times, each time at an interval of about 10 days. At the same time, pay attention to prevent the occurrence of snails, red spiders, citrus whitefly and other pests. Remove excess buds and sprouts from rootstocks. Wipe off the sprouts of the second shoot in time after the first shoot matures, leaving only 1-3 shoots to ensure that there are no branches within 40 cm of the trunk.

Virus-free container seedlings have the advantages of robust growth (figure 5), well-developed fibrous roots (figure 6), high grafting site (not suitable for infection of diseases and insect pests), can be planted in multiple seasons and no slow seedling stage. From the source to control the spread and spread of diseases and insect pests, strong seedlings, easy to enter the orchard early bearing high yield.

Fig. 5 qualified seedlings

Fig. 6 whisker root of virus-free container seedlings

3 specification for safety management of citrus seedlings

Most citrus growers or managers pay attention to the non-virus in the process of seedling breeding, but ignore the disease prevention measures in other links, such as the supervision of virus-free seedling breeding access system and management process, the transportation and planting environment of citrus virus-free seedlings, which should be carried out in strict accordance with the relevant laws and regulations, standards and norms formulated by the state, in order to ensure the healthy and sustainable development of the whole citrus industry. It has become a strong guarantee for the construction of modern citrus industry with "high output efficiency, product safety, resource saving and environment friendly". [Jishan Huayao]