The Biological And Ecological Effect Of Relay Intercropped Garlic On The Continuous Cropping Eggplant Growing In Plastic Tunnel

Continuous cropping obstacle is the main problem in the eggplant(Solanum melongena L.) production in China. Relay intercropping is one of the effective methods to improve the vegetable production in plastic tunnel. As acknowledged, garlic(Allium sativum L.) is a good preceding crop, with broad-spectrum bacteriostatic activity. There are some reports about garlic relay intercropped with crops to alleviate continuous cropping obstacles, but studies on the biological and ecological effect of intercropped garlic on the continuous cropping eggplant in plastic tunnel is uncommon. This study was designed to analyze the biological effect from the growth, yield, nutrient quality, plant enzyme activity of eggplant and the ecological effect from the soil microorganism species and quantity, enzyme activity, nutrition and acid-base properties of eggplant root zone through the field experiment of continuous relay intercropping eggplant with garlic, choose suitable number of green garlic relay intercropped with eggplant through pot experiment, reveal the mechanism of relay intercropped garlic to alleviate the eggplant Verticillium wilt through the antifungal test of garlic root exudates on Verticillium dahliae, and analyze the garlic growth and yield in the eggplant/garlic relay intercropping systems and benefits of relay intercropping, finally build cultivation patterns of eggplant/garlic relay intercropping. The study was aimed at explaining the effect and mechanism of relay intercropped garlic on eggplant continuous cropping obstacle through the biological approach of enriching the crop diversity, and providing technical support for relay intercropping garlic to alleviate eggplant continuous cropping obstacle. The main results were as follow:1. In the field experiment, five treatments were set: eggplant continuous monocropping(CK), relay intercropping with normal garlic(Grow garlic cloves and harvest garlic bulbs. There were two cultivars G110 and G107, denoted by NG110 and NG107), relay intercropping with green garlic cultivar G025 and G064(Grow garlic bulbs and harvest green garlic for several times. There were two cultivars G025 and G064, denoted by GG025 and GG064). Results showed that, relay intercropped garlic improved the chlorophyll content and reduced the content of MDA and the activities of SOD and POD in eggplant leaves. In the fourth year of continuous cropping, the PPO gene expression level in the eggplant leaves in eggplant/garlic relay intercropping systems was higher than that in eggplant monocropping system, which can protect eggplant from continuous cropping injury. In the third experimental year of 2012, the eggplant yield in NG110 and GG064 was respectively 6.3% and 7.8% higher than that in CK. In the fourth experimental year(2013), eggplant yield reduced by relay intercropping garlic. The net income in eggplant/garlic relay intercropping systems was always higher than that in eggplant monocropping system. Moreover, the dry matter and the content of soluble protein and soluble sugar in eggplant fruit were also improved through relay intercropping with garlic.2. Relay intercropping eggplant with garlic can affect the microbial community structure. The number of bacteria, fungi and actinomycetes in relay intercropping treatments was less than that in CK. The results of high-throughput sequencing showed that, in 2012, the OTU number of bacteria in all GG064 treatments was less than that in CK. The relative abundance of Gemmatimonadaceae, Anaerolineaceae, Flexibacter of Flexibacteraceae and Nitrosomonadaceae in all samples was higher. About fungi, the relative abundance of Ascomycota and Cladosporium of Fungi imperfecti was higher, and the relative abundance of Ascomycota was lower in GG064 than that in CK. Different with that in 2012, the relative abundance of Solimonadaceae and Planctomyces of Planctomycetaceae was also higher in 2013. Before eggplant transplant and in the fruiting period, the fungi abundance and community diversity in CK was higher than that in GG064. The result of RDA showed that, the effect of relay intercropping and monocropping was the opposite.3. Eggplant relay intercropping with garlic improved soil enzyme activities and available nutrition content. In 2011, soil invertase activity was significantly improved in relay intercropping system. Soil urease activity and available phosphorus were always improved in the four continuous relay intercropping years. Except in 2010, the soil alkaline phosphatase activity in eggplant/garlic relay intercropping treatments was higher than that in CK, so as the available nitrogen content. Soil available potassium content was improved in relay intercropping system in 2011 and 2012. Soil chemical characteristics changed by relay intercropping. In 2010, soil pH dropped by eggplant/garlic relay intercropping, especially in eggplant/green garlic treatment. Soil EC was significantly improved. In 2011, both soil pH and EC were lower in relay intercropping system than that in CK; in 2012, soil p H in NG110 treatment was always higher than CK, but the GG064 treatment was the opposite; in 2013, the soil EC dropped obviously in the first half year, but the soil pH dropped in the second half year.4. In the same treatment in the four experimental years, soil invertase and urease activities showed upward trend. Relay intercropping eggplant with garlic improved soil alkaline phosphatase activity. The trends of soil available nitrogen and potassium content were rised up all the time, but the available phosphorus content was first up then down. With eggplant continuous cropping, the soil pH decreased continuously, the EC was opposite.5. In the pot experiment, five treatments were set, including relay intercropping one eggplant with 0(T0), 8(T1), 16(T2), 24(T3) and 32(T4) green garlic respectively. In 2013, the eggplant yield in relay intercropping system was about two fold higher than that in CK, and increased with the garlic number. The net income was also higher in eggplant/green garlic relay intercropping system than that in eggplant monocropping system. In this experiment, the more the green garlic number, the higher the net income. In 2012, the net income was respectively 683%, 775%, 782% and 849% higher than CK, and there was 148%, 150%, 160% and 178% higher in 2013. The number of green garlic affected the nutritive element content in eggplant leaves. The dry matter was always the most in T4 treatment. T3 treatment can increase the nitrogen element content in eggplant vegetative growth stage, and it was risen up in most relay intercropping treatments in eggplant/green garlic relay intercropping stage. The content of potassium element increased as the green garlic number increased. Calcium element was accumulated with the growth of eggplant. The content of magnesium element was always increased by relay intercropping, but the copper and zinc elements were always decreased. Relay intercropping green garlic always increased the soil enzyme activities and available nutrition content, Within the scope of number of green garlic in this test, the more the green garlic, the better the effect.6. Garlic root exudates notably inhibited the mycelial growth of Verticillium dahliae. The net growth of mycelia gradually declined with the increasing concentration of garlic root exudates. The inhibition rate can reach 35.0%. Through scanning electron microscope, we can observe that, the mycelia grown in Potato-Sucrose-Agar medium(CK) showed normal morphology, which was tubular with less wrinkle and many spores. After treated by garlic root exudates, most mycelia broke into small parts and even melted; shrunken and distorted mycelia were observed with wrinkle, sunken and small holes on the cell wall, and without spores.7. In the antifungal test, five treatments were set, including planting 0(CK, G0), 8(G8), 16(G16), 24(G24) and 32(G32) green garlic. After inoculated with spore suspension of Verticillium dahliae, planting 24 green garlic had the best inhibitory effect. The morbidity of Verticillium wilt was only 11.1%. Compared to G0, green garlic increased the number of soil microorganism, and the number of bacteria and actinomycetes increased with the increasing number of green garlic, but the number of fungi was the opposite. The community diversity of bacteria was the highest in G32 treatment after green garlic grown(P team). Tree diagram showed that, the species composition of bacteria in CK and green garlic treatments was greatly different and had greater difference with original soil. From heatmap we can see that, the relative abundance of Lactococcus of Lactobacillaceae and Methylophilaceae was higher in original soil than that in the soil of P team; Algoriphagus in P team was not found in the soil after inoculated. From PCA diagram we can see that, the bacteria community composition of the soil planted green garlic has great difference with CK. The number of fungi in green garlic treatments was less than that in CK. There was 139 microsclerotia in original soil. The number of microsclerotia decreased after cold winter in all treatments. Green garlic inhibited the microsclerotia growth obviously in G32 treatment.8. In the antifungal test, the PPO and PAL activity and MDA content in eggplant leaves was lower in green garlic treatments than that in CK, showing that green garlic protected eggplant from the outside injury. The PPO gene expression level was 7.40, 3.81, 2.42 and 3.38 fold in green garlic treatments than that in CK.Synthesize the above results, we can see that, relay intercropping with normal garlic or green garlic can alleviate eggplant continuous cropping obstacle; the system is an efficient and sustainable production models in eggplant production under plastic tunnel. The mechanism was related to the allelopathy of garlic root exudates to eggplant growth and biology, soil microbial community structure, soil enzyme activity and nutrient availability and the inhibition effect to eggplant Verticillium dahliae.