| As a new sort of biologic fertilizer since late 20 century, arbuscular mycorrhizal fungi (AMF) exists in almost all kinds of soils and forms symbiosis with nearly all families of the angiosperms. Most of the crops, fruit trees, vegetables, ornamental plants and flowers can form arbuscular mycorrhizae.The function of AM fungi between plant and soil is being a bridge, and it is the carrier of matter transport. As the carrier of matter transport from plant to soil or from soil to plant, it is very important to the development and health of plant and soil.Plant mycorrhiza and mycorrhizal fungi are being studied in many countries because of their significance in sustainable agriculture and reconstructive ecology recently. Citrus generally do not take root hair in the soil , mainly relying on its symbiotic fungi in order to doing the absorption nourishment. Peyronel (1922) first discovered citrus plants exist the mycorrhizal . a large number of experiments prove that most citrus plants can form mycorrhizal fungi which effects on the citrus significantly, promoting growth , improving fruit quality and increasing root of mineral nutrient uptake and utilization, mycorrhizal fungi exist different of varieties citrus .Genetic transformation experiments of the different exploids from the seedling of axenic lemon and trifoliate infected with Agrobacterium rhizogenes were carried. The optimizing culture system of Ri T-DNA transformed roots for limon was constructed as follows: After the ventral wounded striations on the single activation cotyledon were inoculated by A. rhizogenes A4 (logarithmic period), they were cultured at the temperature of 25℃±2℃in darkness for 25～30 days, some transformed roots were generated from wounded striations of most cotyledons. The genetic transformed ratio is about 84±10%. Axenic Ri T-DNA transformed roots (hairy roots) were harvested after five subcultures. Explants were actived on MT medium. The MS medium was used for subculture of transformed roots. Mass Ri T-DNA transformed roots which the hormone was produced independently were harvested from this optimizing culture system. White fresh Ri T-DNA transformed roots were about 1.2±0.08cm long, 0.72±0.06mm wide, and growed negative geotropism.The researchs on arbuscular mycorrhiza of Citrus limon much contribute to the citrus ecophysiology. The axenic seedling of Citrus limon was inoculated with different species of AM fungi. We tried to study the effect of different AM fungi on vegetable growth and mineral contents in Citrus limon seeding, and to pick out the most suitable AM fungi species. Some theoretical foundation was partially supplied for the application of AM fungi.Pot experiment of axenic Citrus limon seedlings inoculated with different AM fungi Gigaspora margarita, Glomus mosseae and Glomus versiforme respectively was carried, and both vegetable growth and mineral contents were analyzed. The results showed that the seedlings inoculated with AM fungi could be colonized effectively, and the vegetative growth was improved significantly compared with that of the non-mycorrhizal control, such as shoots and roots, especially fibrous roots. Compared to the control, the root length and the lateral root number in the treatment of inoculation with AM fungi Glomus mosseae were 23.8% and 36.9% higher, and the fibrous root number and length were 170.2% and 102.1% higher. Mineral contents of N, P, K, Ca, Mg, Zn, Cu and Mn were also elevated significantly in leaves of seedlings inoculated respectively with these AM fungi. For example, the contents of P were increased by 47.2%, 89.1% and 33.1%. Seedlings of inoculation with Glomus mosseae grew best vigorously, and both the mycorrhizal dependence and the contents of N, P, K, Ca, Zn and Cu were the highest level among the three treatments. The effective order of AM fungi species on Citrus limon seedlings decreased in the following order: Glomus mosseae > Gigaspora margarita >Glomus versiforme. The positive effect was observed from all treatment seedlings with the 3 AM fungi species. and the most suitable species among the three AM fungi species for Citrus limon seedlings was Glomus mosseae.In southwest region of our country ,water shortage and uneven distribution causes a great influence. Drought stress reduction plant output and quality, or even caused devastating damage. Citrus wide spread in in southwest area ,has an important position to the economy of rural and is the farmers main economic income. Limon greatly helps to farmers income increase of Sichuan. However, Limon output and quality instability, because the southwest region often suffer drought and high temperature weather recent years. AMF (arbuscular mycorrhizal fungi, AMF or AM fungi) is very significant on plant growth and health, can promotes plant growth, improve fruit quality, increase root of mineral nutrient uptake and utilization. AM fungi in the non-high-temperature conditions for plant growth and increase plant-physiological and biochemical indicators of stress research has been a some reports, but the reaserch on different species of arbuscular mycorrhizal fungi interaction with the limon drought-resistant effect has not been reported. I view the Yangtze River in southwest China's citrus belt in the summer exposed to high temperatures and drought victims citrus tree Status, Three species of AM fungi Gigaspora margarita,Glomus mosseae and Glomus versiforme on limon sterile seedling mycorrhizal formation and the impact of drought tolerance, AM fungi for biotechnology in the Three Gorges reservoir area limon drought resistance of breeding for southwest and mycorrhizal of nursery limon efficient good bacteria provide a theoretical basis .The pot experiment for the effects of arbuscular mycorrhizal fungi (AMF)Glomus versiforme,Glomus mosseae,Gigaspora margarita on drought-resistent of the seedlings of Citrus Limon was carried. The results indicate AMF increased plant growgh ,enhanced the SOD and POD activity of leaves and root systerm activity, improved the contents of soluble sugar and soluble protein, reduced the content of MDA, diminished membrance permeation, heightened the drought-resistent ability of limon seedlings. Comparing the three AMF species, the effects's compositor is Glomus versiforme < Glomus mosseae < Gigaspora margarita. We think that Glomus mosseae is the feasible and excellent fungi for Shatian You seedlings to withstand the drought.
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