Screening Of Trifoliate Orange Pure Clones And Improvement Of Citrus Nursery Substrate And Container

Trifoliate orange [Poncirus trifoliate (L.) Raf.] is the most important citrus rootstock in China. In citrus nursery production, however, the rootstock seeds are almost all from mixed seed sources, leading to high variability of rootstock seedling growth and the effects on scion cuotivar grwth and development. There is not any rootstock seed mother block. It is obvious that selection of pure clone of the main rootstock is indispensable for citrus industry. Virus-free container nursery is the basic safety requirement for citrus cultivation. This technology faces various charllenges. The widely used container medium contains peat, which is quite expensive and damages the environment. Seeking for substrates of low price and easy availablility is urgently necessary. Meanwhile, containers of low price and suitable forseedling growth are also required in nursery plant production. The purposes of the present thesis aim at the selection of trifoliate orange pure clones having the seedlings of identical genetic background with good propagation characters; screening of substrates to replace peat, and containers of low cost and suitable for citrus growing. The mainly results as follow:1. Investigation on citrus seedling-raising technique based on virus-free containersInvestigates the current situation of citrus seedling-raising based on virus-free containers in main citurs producing areas. The result showed that citrus seedling are still mainly raised in open field in these areas. It shows seedling nursery technique, there are wide range of base material recipes, container, rootstock breeding, fertilize and irrigation in those areas. Immediate producing costs and labor costs are the manly costs of container nursery. Substrates and containers costs are the main costs in immediate producing costs.2. Selection of trifoliate orange pure clonesDifferent trifoliate orange clones were sampled in Hunan province. DT1, DT2, DT3and DT4were collected from Datian village, Dongkou county, Longhui6was find in Longhui county, Jishou2and Jishou3from Citrus Research Institute of Xiangxi. Using mixed seeds used in nursery production as the control, the main propagation characteristics of all the trifoliate orange clones were tested. The results showed that DTI, DT3and DT4clones had the average seed quantity per fruit (about35seeds/fruit), the weight of1000seeds, seed germination rate (over80%) and seedling emergence rate (90%)better than others and the mixed seed sample. The seedlings of the3clones showed faster and more uniform growth. The net photosynensis of the three clones was superior to others. SSR marker analysis results indicated that the genetic background of the seedlings are consistency.3. Screening of container substratesEight types of materials including virgin soil, sand, sawdust, mushroom sustrate residue, Chinese medicine residue, citrus peel residue and bio-charcoal were evaluated in the present experiment to make suitable substrates in comparison with peat-containing medium. After analyzing the physic and chemical properties of each single materials,34kinds of composted media were formulated, whose physic and chemical properties were further analyzed. According to the physical property. Seedling growth was determinated by regular measurement of plant height, stem diameter and leaf area. Two out of the11media, i.e.virgin soil:sawdust:bio-charcoal=3:3:1and virgin soil:medicine residues:bio-charcoal=3:3:1gave the best growth results as that sand:sawdust:peat=1:2:1. The medium pH had important affects on seedling growth.Bio-charcoal was made by high temperature with pruned materials, and it showed excellent effects in citrus nursry production. The results indicated that container substrates without peat could be obtained by using bio-charcoal as one component.4. Container selectionThree types of containers were used in experiment, including Type I high and narrow, Type III wide and short, and the Type â…¡ in the middle. The results suggested that Type II container was cost reasonable, and of better effects on seedlings growth in comparison wth the others. Therefore, the Type â…¡ container was recommended.