Screening Of J-28 Strain Against Phytophthora Infestans And Compound Inhibitory Effects Of Several Antagonistic Strains

Potato is a crop with cold-resistance,drought-resistance,poor-resistance,adaptability,and rich in dietary fiber,low in fat,it can help to control personal weight gain,prevent high blood pressure,high cholesterol and diabetes.According to the Ministry of Agriculture,China will launch potato staple food strategy,and more than 50% of the potato will be consumed as the staple food in 2020.And potato will be processed into bread,pasta,rice and others to be used.Potato will become another major food crop beside rice and wheat.However,potato often suffers harm from many diseases during its growth and development.Especial from the1980 s,potato late blight caused by Phytophthora infestans,due to its frequency and prevalence popularity,has become a major obstacle.The disease may lead to death or rot of potato leaves,stem and tuber.At present,The control measures of potato late blight include artificial cultivation management,improved varieties,pathogens infection resources control,chemical and biological control,etc.Wherein Microbial Control has many advantages:non-pollution,no residues and no drug resistance.At the same time,because of the huge population of microorganisms and many kinds of antagonistic strains,etc.,it has a large market and research value,and is concerned more and more attention by the researchers.But,a single antagonistic bacterium is difficult to effectively play the role of prevention and treatment in field control.This phenomenon is usual to the plant disease control until now,so some scholars try to put more antagonistic microorganisms together,and achieved good results in plant disease control.The main aims in this paper consist of following aspects:(1)Screening,isolating and identifying the antagonistic strain which is stable and effective in inhibition P.infestans from potato field;(2)Preliminary studying antibacterial activity of antagonistic bacterium J-28 against P.infestans;(3)Making clear the effect of J-28 strain on the germination of P.infestans spores and the disease prevention effect on the detached tissue;(4)Exploration of the feasibility of J-28,SR13-2 and Sy11 antagonistic strains compound against P.infestans;(5)Comparative research of the stabilities between complex broth of three antagonistic strains and J-28 broth.The main research results were as follows:1.Sixty strains were isolated from potato rhizosphere soil in Mazhuang Village,Dongjinzhuang Township,Beishi District,Baoding City,Hebei Province.Among which,16 strains had antagonistic activities against P.infestans mycelia growth,and the inhibition rates of these strains reached more than 60%.Of them,J-28 strain was the most stable in anti-oomycetes.The inhibition rates of living strain,bacterial liquid and free cell fermentation fluid were 87.80%,81.36% and 82.92%,respectively.The J-28 strain was identified as Bacillus megaterium by biochemical properties and 16 S r DNA gene sequencing.2.Anti-oomycetes way of J-28 strain was preliminarily studied.Mycroscopy observation found that J-28 strain could make breakage of P.infestans mycelium.The antagonistics effect of J-28 strain was growth suppression rather than killing to pathogens;On the other hand,J-28 strain intracellular could secrete some antibiotic substances which inhibited P.infestans;Prohibitive substances of J-28 strain cell-free fermentation liquid could be extracted with 60%ammonium sulfate precipitation;Biuret and ninhydrin reaction of extracted substances were positive and indicating that these substances may be proteins or polypeptides.In addition,J-28 strain could produce protease but no cellulose.3.Effects of bacterial liquid of J-28 strian on germination of P.infestans spores and the disease prevention effects on in vitro potato tissue were tested.The results showed that release and germination of zoospores and direct germination of sporangia were significantly restrained by J-28 strain;The disease prevention effects were optimal,the protection rates of tubers and leaves were 72.72% and 78.56%,respectively.4.The feasibility of compound fermentation or formulation of three strains including J-28,SR13-2 and Sy11 were investigated by their inhibition effect on P.infestans mycelia growth and optimized preliminarily.The results showed that formulation culture liquid of 3trains obtained the strongest inhibition rate,the formulation was that compound fermentation liquid of J-28 and SR13-2 coculture 24 h at same volume mixed with Sy11 liquor for separate culture 3 days at 4:1,and the inhibition rate reached 93.75%,which was higher than that of any single strain.5.The inhibition stabilities of formulation and J-28 bacteria liquid against P.infestans were explorated,after dealt with different treatments.In comparison with J-28 bacteria liquid,the inhibition rates of formulation liquid still remained over 90.00% after treatment with different p H,temperature,ultraviolet irradiation,and over 80.00% with metal ions and protease.The formulation liquid showed better stability than J-28 single bacteria liquid.