Research On Allelopathy And Allelochemicals Of Garlic Root Exudates

As one of the traditional vegetables and advantage garden crops in China, cultivated area and output of garlic rank the first place in the world. Being a universally accepted fine front stubble crop, garlic root exudates is one of the factors which affect the next stubble crops. Research has been done on the antibacterial action of garlic bulb, but whether garlic root exudates has allelopathy and the mechanism of garlic functioned as a fine stubble crop are not clear. So allelopathy of garlic root exudates, rhizospheric effects and allelochemicals were researched systemically in this experiment to reveal effective mechanism, and provides the theoretical basis to work out vegetable cultivation system. The main results were as follows.1. The water culture method was used to collect garlic root exudates. Allelopathy of two garlic cultivars root exudates were researched by lettuce seed germination test experiment, compared the effects of seed germination, seedling growth and subjection value. The results showed that both of this two garlic cultivars root exudates have allelopathy which increased at lower concentrations (0.1,0.2 g?mL-1) of garlic root exudates, but decreased at higher concentrations (0.4,0.6 g?mL-1). The promotive effect of white skin garlic (G25) and purple skin garlic (G88) root exudates were the strongest when the concentration were 0.1 g?mL-1 and 0.2 g?mL-1 respectively. The inhibition of G88 was stronger than G25 at high concentration. Allelopathy of G88 root exudates was higher at the earlier stage than which at the later stage.2. The inhibitive effects of two garlic cultivars root exudates on Fusarium oxysporum f. sp. Cucumerinum and Fusarium oxysporium f. niveum Snyder et Heansen were studied by measuring the inhibitive effects on pathogen spore germination and mycelia growth in lab culture dish. The result showed that the inhibitive effects on pathogen mycelia growth and spore germination were increased with increasing of garlic root exudates concentration, and the inhibitive effect of G88 was higher than that of G25. The reaction of Fusarium oxysporum f. sp. Cucumerinum was more sensitive than Fusarium oxysporium f. niveum Snyder et Heansen.3. The changes of rhizosphere microbes and soil enzyme activity of the two garlic cultivars at different stage were studied. The result showed that garlic root exudates could increase the growth of bacteria, fungi and actinomycetes, and advanced the activities of urease, acid phosphatase and catalase in garlic rhizosphere soil. Therefore, it improved the nutrition element turnovers and circulation such as nitrogen and phosphorus in garlic rhizosphere soil, and created the fine rhizosphere nutrition environment.4. The allelopathy of garlic (G88) root exudates on Chinese cabbage, hot pepper, cucumber, tomato and radish was researched by bioassay on seed germination, seedling growth and enzyme activity. The result showed that the seedling growth of receiver crops was increased at lower concentrations, but decreased at higher concentrations. Radish was the most sensitive one of the receiver crops, the next was tomato. The sensibility of cucumber was the worst.5. To avoid the influences of soil and microorganism, allelopathy of garlic root exudates was studied by means of tissue culture and water culture which simulated crop rotation and intercropping in the field. The result showed that these two methods were feasible on the research of allelopathy of garlic root exudates. At the same, garlic root exudates could accelerate seedling growth of the receiver crops through increasing root activity, chlorophyll content, photosynthetic rate, nitrate reductase activity and nutrients absorption ability. These two methods proved that allelochemicals could operate directly on the receiver crops, and provided a clue for the mechanism which the garlic as a fine front stubble crop.6. Garlic root exudates was collected from agar culture, water culture and sand culture in this experiment, and be extracted by ethyl ether, ethyl acetate, chloroform and n-butanol. The results of each fraction bioassay showed that allelopathy of ethyl acetate fraction in root exudates was the strongest, the next was chloroform fraction. The ethyl ether and n-butanol fraction showed no allelopathy. The results proved the varieties and quantities of allelochemicals in garlic root exudates were vary in this three culture manners, and sand culture was most, then next was water culture, followed was agar culture.7. The results showed that the allelopathy of ethyl acetate fraction was the strongest. GC/MS analysis showed the dominating allelochemicals was butylated hydroxytoluene in agar culture, butylated hydroxytoluene and 2,6-bis(1-methylethyl)- phenol in water culture, dibutyl phthalate, butylated hydroxytoluene and 2,6-bis(1-methylethyl)- phenol in sand culture. Diallyl disulphide was identified in these three cultures, which is a representative matter in volatile of garlic and has antimicrobial activity. So this matter is concluded one of the allelochemicals.8. Finally, butylated hydroxytoluene and 2,6-bis(1-methylethyl)- phenol, which were replaced by exogenous organic compound, were proved to be allelochemicals by bioassay. Allelopathy of butylated hydroxytoluene was higher than 2,6-bis (1-methylethyl)- phenol at high concentrations (500,1000mg?L-1) and both of them were not obvious at low concentrations (50,100mg?L-1). Allelopathy of diallyl disulphide, which was replaced by volatile of garlic, was existent. When the time of seed soaking was 10s, volatile of garlic could increasingα-amylase activity which speed seed germination and inhibiting IAA oxidase activity which promoted seedling growth.