| Winter wheat-summer corn double cropping is the main grain cultivation method inHebei province. The new farming methods that maize straw returning to field had began tobe promoted in Hebei province since the mid-1990s. The area and the number of maizestraw returning to field were gradually rising, as well as the wheat sharp eyespot which hasbecome more and more serious and the second-largest wheat diseases in Hebei province. Inthis paper, on the basis of detailed investigation and analysis of the change of WheatSheath Blight before and after maize straw returning to field in Hebei Province, thecomposition and pathogenicity of differentiation characteristics were studied. At the sametime, simulation experiments in laboratory and field experiments were conducted to studythe effects of maize straw on diversity of microorganisms and antimicrobial substancescontent in wheat root domain. The type and content of main allelochemicals indecomposed products of Maize straw was determined by the GC/MS technology, and theallelopathy of main allelochemicals on wheat seedlings and R. cerealis were analyzed.Finally, the control effects of versatility of antagonistic bacteria B1514, thifluzamide, anefficient chemical fungicide, and fertilization on wheat sharp eyespot were studied byindoor potted plants and field experiments. The main results as bellows:1. Before the implementation of a large area of maize straw in Hebei Province, WheatSheath Blight occurred with a large area only once in1989. The incidence area and yieldlosses were up to584,000hm2times and about17,000tons, and the occurrence area wasless than3,000hm2times. The occurrence area of Wheat Sheath Blight was671,000hm2times every year, and the average annual yield losses was2.1million tons after the newfarming methods was carried out that maize straw returning to field. The occurrence area inHebei showed that the characteristics of weight north and light south. The incidences ofHandan, Xingtai, Shijiazhuang and Hengshui were severe, and Baoding, Cangzhou, andTangshan were mild.2.196Rhizoctonia strains were isolated from the three regions and were belong tofive anastomosis groups including AG-D, AG-B(0), AG-2, AG-5and AG-4, with theamount173,3,10,7and3, accounting for88.3%,1.5%,5.1%,3.6%and1.5%,respectively. The virulence of196Rhizoctonia strains could be divided into four pathotypes with the disease indexes56.08,48.42,42.77and25.95, respectively, and thepathogenicity of the isolates against Triticum aestivum was in the order of Shixin828>Liangxing99> Han6172. The virulence of isolates from Handan were stronger than thatof isolates from other districts, significantly, with the highest average disease index52.16,followed by the isolates from Cangzhou, Shijiazhuang and Baoding in turn, and thevirulence of isolates from Tangshan was the weakest with the average disease index41.12.3. Maize straw returning to field was favor to the occurrence of Wheat Sheath Blight.The number of R. cerealis in the rhizosphere and root surface soil was increased about33.3%to83.8%after the Maize straw was returned to field, significantly. Under thecondition of Maize straw returning to field, it was easier and faster that the wheat wasinfected by the R. cerealis, and the time was shortened about3to6days. The occurrenceof Wheat Sheath Blight was more serious with Maize straw returning to field at the level of18000kg·hm-2and9000kg·hm-2. At the jointing stage, the number of G+bacteria, fungi,the ratio of fungi and bacteria were increased in wheat rhizosphere and root surface soil,significantly. But, the number of G+bacteria was decreased. In addition, the ratio ofantagonistic bacteria to the total and the content of2,4-DAPG in the wheat rhizosphereand root surface soil were also reduced.4. The wheat seed germination was inhibited by the decomposed products of maizestraw, and the inhibition effects become stronger when the concentration graduallyincreased. The growth of wheat seedlings was inhibited at the higher concentrations ofdecomposed products but promoted at the low concentrations, and the roots growth wasmore sensitive than the aboveground parts.With the improvement of the concentration of decomposing products, wheat rootactivity, SOD and POD activities were all gradually reduce, but the root ion leakageenhanced, significantly. After being cultured till the25thgeneration on the culture mediumcontaining the decomposed products of maize straw, the pathogenicity of R. cerealisenhanced, significantly. When the Rhizoctonia strains were cultured till40th, thepathogenicities of four different types virulence, including Rhizoctonia RV1, RV2, RV3and RV4, were significantly enhanced and the disease index of wheat infected by the40thof Rhizoctonia strains were improved by20.0%,37.9%,42.9%and72.6%than that of theparents, respectively.5. Based on comparison of retention time and mass spectra with those of authenticsamples,42peaks were identified, including organic acids, esters, amides, hydrocarbons,aldehyde-ketones ketones, phenols, alcohols and heterocyclic compounds, with theproportions23.16%,21.6%,13.56%,12.84%,8.64%,2.16%,0.36%and3.48%,respectively. The main compounds were thirty-four alkyl, carboxylic acid decyl ester,salicylic acid, N-ethyl-acetamide,3,5-dimethyl-benzaldehyde, dibutyl phthalate,2-methyl-pentyl-isobutyl phthalate dibutyl and3-phenyl-2-Acrylic acid. Among the12selected compounds, the content of Salicylic acid was the highest withthe concentration of32.41mg·L-1, followed by3-phenyl-2-acrylic with the concentrationsof21.31mg·L-1. The concentrations of Hydroxybenzoate,4-hydroxy-3-methoxy-benzoicacid, Hexadecenoate and8-octadecenoic acid were10.32mg·L-1,9.11mg·L-1,8.48mg·L-1and9.13mg·L-1, respectively. The content of4-methoxy-anthranilic acid was lowest withthe concentration of0.43mg·L-1.The inhibitory effect of Salicylic acid on the growth of wheat seeding was thestrongest among the12compounds, followed by the Hydroxybenzoate.3-(4-hydroxy-3-methoxyphenyl)-2-Acrylic had the strongest promotion effects on the mycelium growth,dry weight of mycelium, sclerotium number and dry weight of R. cerealis, followed by4-methoxy-anthranilic acid. But, the colony diameter, sclerotium number and dry weightwere inhibited by the4-hydroxy-3-methoxy-benzoic acid.6. The results showed that B1514could colonize in rhizosphere and in root more than49and28days after treatment by soaking seed with fermenting broth, respectively, and thecolonization time could be lengthened by adding maize straw into the soil. The controleffect of soaking seed with B1514was lower than that of Tebuconazole at the dose of150g/100kg, significantly, in pot experiment, and was85.3%when the maize straw wasadded into the soil with no significant difference compared with that of Tebuconazole. Infield experiment, the persistence of seed soaking and fermentation product of B1514waslonger than that of Tebuconazole at maturity stage with the control effect of55.2%and thedegradation rate of45.5%.7. The sensitivity of all strains collected from the area in Hebei province to the sixdifferent fungicides was determined by mycelia growth inhibition method. The order ofsensitivity to those from high to low was Tebuconazole, Thifluzamide, Fludioxonil,Propiconazole, Triadimefon, Jinggangmycin and Carbendazim. The results showed that thefrequency of strains with different sensitivity to Trifluzamide distributed as a unimodalcurve, and there was no sub-group with declining sensitivity. The mean EC50value was0.072±0.022μg/mL and it could be considered as the baseline sensitivity. Five resistantmutants of R. cerealis to Trifluzamide were obtained by UV mutagenesis with theresistance levels ranging from5.48to18.94fold. No cross resistance relationship existedbetween Trifluzamide and other six fungicides. The virulence of five resistant mutantssignificantly weakened to Shixin828and Liangxing99than the parent isolates, respectively,except for the virulence of resistant mutant HD7-7U to Shixin828, and the resistance offive mutants could not be inherited stably. So, it was suggested that R. cerealis had a low tomedium risk of developing resistance to Trifluzamide.8. The control effects of seed dressing with80mL24%Thifluzamide SC per100kgseed were69.7%at jointing stage, and56.1%at maturity stage, respectively, much morebetter than the control effect of seed dressing with Tebuconazole at the dose of150mL/100 kg. The increase rate of seed dressing with Thifluzamide SC was6.58%and much higherthan that of seed dressing with Tebuconazole.9. When the number of basic seedling wheat was3.75million hm-2and4.5millionhm-2, with the ratio of base to topdressing nitrogen5to3, the disease severity of WheatSheath Blight was weaker, with the incidence from21.2%to24.3%and disease index from13.2to15.1. The yields of wheat were7110.5kg/hm2and6965.3kg/hm2, respectively.The control effect of potassium was better when it was used as the base fertilizer with theamount of135kg/hm2. |
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