| China is one of the most important producting country of protected vegetablein the world.Meantime, protected vegetable is the most dynamic industry in agriculture of China, playing akey role in the development of modern agriculture. However, many greenhouse crops sufferfrom attack by nematodes, soil-borne pathogens as well as to competition from weeds,especially in monocropping systems. The risk of nematodes and soil-borne epidemic whencrops are grown under such intensive regimes is high, and often results inreduction ofquantity and quality of vegetables. At present, the standard treatment for the management ofnematodes, soil-borne pathogens and weeds in many high-value crop production systems ispreplant soil fumigation with methyl bromide (MB). However, developing countries arecommitted to totally phasing out MB production and use by2015due to its detrimental effectson stratospheric ozone. The absence of MB from market will impact agricultural, silvicultural,and horticultural production unless safe and efficacious alternatives are found. Based on ourprevious study,1,3-D (1,3-dichloropropene), is one of the potential candidates of MB as a soildisinfectant. However, due to the limitation by the current level of economic development,many advanced fumigant application methods and much of the equipment cannot be used inChina. As one of the most promising short-term alternatives to MB,1,3-D is going to beregistered as preplant fumigant in China. Therefore, in this study,a series of laboratory test,greenhouse pot experiment and field trials were conducted to determine thebioactivities of1,3-D for its potential to control nematode, soil-borne pathogens andweeds.Meanwhile,traditional physiological and biochemical methods, associate with T-RFLPandhigh-throughput DNA sequencing (Roche454GS FLX+) were used to determine theeffects of1,3-D on soil culturable microorganismspopulation, enzyme activities and microbialdiversity to obtain microorganism flora and species richness at different levels. The results ofthis studywill evaluate the bioactivities and ecological safetyof1,3-D,offering a theoreticalfoundation to the use of1,3-D on greenhouse vegetable industry. The results were as follows:1. Laboratory toxicity results showed that the LC50and LC90of1,3-D to second-stagejuveniles (J2)of Meloidogyne incognitawere1.20and3.74mg/L, respectively. Dose-responsestudies found that the seeds of Digitaria chinensis were the most sensitive to soil fumigationwith1,3-D, followed by Eleusina indica, Echinochloa crusgalli and Amaranthus retroflexuswith the LC90values between14.23and73.59mg/kg soil. Among the pathogens,Phytophthora capsici was the most sensitive and Fusarium oxysporum was the least sensitiveto1,3-D fumigation with the LC50values were0.24and1.55g/m2. Rhizoctonia solani, Phytophthora nicotianae and Botrytis cinerea exhibited intermediate susceptibility.2. Field trials in tomato and cucumber were conducteddetermine the efficacy of1,3-D(90,120and180L/ha) for its potential to control nematode, soil-borne pathogens and weeds.The results revealed that1,3-D exhibited excellent control effects to M. incognita while withcertain yield increase. In both trials,1,3-D at the doses of120and180L/ha were as effectiveas MB in increasing plant height, vigor, tomato yield and in reducing the incidence ofsoil-borne disease, especially in maintaining excellent nematode control efficiency, but itproviding relatively poor control over weeds.3.Traditional physiological and biochemical methods were used to determine the effectsof1,3-D on population of culturable microorganisms and soil enzyme activities. The resultsshowed that all doses of1,3-D exhibited a inhibition initially and then recovery. There wereno signifant effects between fumigation treatments and the control. The activities of theurease,invertase,hydrogen peroxidase,dehydrogenase, acid phosphataseand FDA hydrolyticactivity were also investigated. The results showed that all doses of1,3-D exhibited ainhibition initially and then recovery. There were no signifant effects between fumigationtreatments and the control in the end.4. T-RFLPresults showed that there were23main TRFs in different sampling time. At5WAT,1,3-D exhibited a inhibition effects to soil bacteria. While, at10WAT, bacteriarecovered and stimulation effects developed. At15WAT,there were no signifant effectsbetween fumigation treatments and the control.5. To the best of our knowledge, this study is the first application of PCR-based454pyrosequencing to characterize fumigating soil samples.454sequencing results revealed thatProteobacteria, Bacteroidetes, Actinobacteria, Acidobacteria and Firmicutes werepredominant phylum in soils. Bacterial diversity was affected initially, while recovered in thelater treatments and soils from1,3-D treatment plots had a more bacterial diversity.1,3-D hadonly a short-term and transitory impact on the indigenous soil microbial community, andapplication of1,3-D fumigation would stimulate the proliferationof some microbialpopulation. |
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