The Mechanism And Ecological Management Model Of English Grain Aphid And Fusarium Head Blight Occurred In Wheat Field

As an important staple food crop, wheat?Triticum aestivum L.? is one of the most widely cultivated crops in the world, and its cultivated area is about more than 21,500 hectares. In nature, plants are most likely challenged by different herbivores and pathogens sequentially or simultaneously. The English grain aphid Sitobion avenae Fabricius?Hemiptera: Aphididae?and Fusarium head blight are two commonly occurring pests on cereal crops worldwide,especially in Europe, Asian. Currently, most of the studies only concerned about one kind of disease or herbivore, however, it is difficult to understand the model and mechanism of ecological regulation pests in wheat field ecosystem. To reduce the damage caused by pests and the usage of chemical pesticides, the ecological management model of English grain aphid and fusarium head blight should be constructed. The current study focused on excavating and transformation resistance genes expressed in wheat to breed novel cultivars,using the wheat resistance induced by pests, screening the candidate genes associated to reduce pathogenic or knock-out the candidate genes related to strength pathogenicity. In this way, the findings will help in constructing the ecological model and provide a theoretical basis for controlling them. The important conclusions are as follows:1 In the ecosystem of wheat field, the resistant wheat genotypes have evolved series strategies to reduce the damage asused by cereal aphid. This study proved that the tolerance was the main category of resistance in genotype XN98-10-35 to S. avenae. The six candidate genes expressed in this genotype were blasted in different genome databases. Although these expressed sequences were likely associated with S. avenae resistance, there was 1 expressed sequence tag located on 7D Chromosome, and its potential function may associate with the ability to maintain photosynthesis in wheat. That serves as an active way for tolerant common wheat with resistant to S. avenae.2 In the ecosystem of wheat field, S. avenae typically infests cereal plants later than Psammotettix alienus Dahlbom?Hemiptera: Cicadellidae?. Therefore, an understanding of the interactions between previously attacked plants and subsequent herbivores will provide a new measure to control the damage caused by the subsequent herbivore. The objective of this study was to examine the fitness of the apterous aphid Sitobion avenae when fed spring wheat that was previously attacked by the leafhopper Psammotettix alienus with evaluation of the differences in aphid weight?WD?, development time?D?, mean relative growth rate?MRGR?,daily production of nymphs?MDNP? and intrinsic rate of population increase?rm? under controlled greenhouse conditions.The results revealed that the fitness of the aphid S. avenae was adversely affected when reared on the two spring wheat cultivars that were previously infested with P. alienus.3 Fusarium graminearum is a devastating fungal causing fusarium head blight?FHB? of wheat and cereal crops. This fungus can produce indole-3-acetic acid?IAA? and a very large amount of IAA accumulates in wheat head tissues during the first few days of infection by F.graminearum. Using liquid culture conditions, we have determined that F. graminearum can use tryptamine?TAM?, indole-3-acetonitrile?IAN? and indole-3-pyruvic acid?IPA? as biosynthetic intermediates to produce IAA. It is the first time a Fusarium species is shown to use the L-TRP-dependent TAM, IAN and IPA pathways rather than the indole-3-acetamide pathway to produce IAA. However, supplying the L-TRP did not lead to IAA production and the final product was TOL.4 15-ADON is a very important mycotoxin secreted by F. graminearum, reducing the concentration of 15-ADON is a major task for wheat production. In the current study, we focused on understanding the relationship between the high concentrations of IAA and substrates of IAA production and the concentration of secreted 15-ADON in F. graminearum under controlled greenhouse conditions. The results revealed that the high concentrations of IAN posed adverse effects on secreting the 15-ADON. Additionally exogenous IAA, TAM and IAN inhibited mycelial growth; IAA and IAN also affected the hyphae branching pattern and delayed macroconidium germination. IAA and TAM had a small positive effect on the production of the mycotoxin 15-ADON while IAN inhibited its production.5 According to the results attained from the microarray analysis, among the up-regulated candidate genes in auxin-inducing conditions, 12 candidate genes was chosen to further determine their functions in IAA biosynthesis. There were 9 genes, including FGSG 01285?related to ARO8- aromatic amino acid aminotransferase I?, FGSG₀1572?related toprobable glutamate decarboxylase?, FGSG₀5295?related to related to aromatic-L-amino-acid decarboxylase?, FGSG₀9834?related to probable pyruvate decarboxylase?, FGSG₁0677?related to related to peroxisomal amine oxidase?copper-containing??, FGSG₀1698?related to related to nitrilases, putative pseudogene?,FGSG₁025?related to probable nitrilase? NIT3??, FGSG₀0821?related to probable nitrilase?, FGSG₀3936?related to probable UGA2- succinate semialdehyde dehydrogenase?were inactivated by replacing it with the selective marker hygromycin phosphotransferase using the USER cloning technique and Agrobacterium tumefaciens- mediated transformation in the F.graminearum strain DAOM 233423. But the remainder didn't get the deleted mutants. There were several candidate genes including FGSG₀1285, FGSG₀5295,FGSG₀1572 and FGSG₀9834, referred to IAA or TOL biosynthesis in F.graminearum,meanwhile their 15-ADON also adversely affected. However, the mutants of FGSG₀1698,FGSG₁0250 and FGSG₀0821 were significantly increased the concentration of 15-ADON.Those candidate genes might regulate the expression of 15-ADON production. The remainder didn't engage in these pathways.6 Both HPLC and microarray technique were employed to analyze the filtrates to determine the products and the expression profiles of candidate genes involved in L-Trp-treatment. The results revealed that in culture, F. graminearum was able to produce TOL when supplied with L-tryptophan. Gene expression profiles were obtained by using microarray analysis of RNAs from F. graminearum cultures in TOL producing conditions.The differential expression profiling revealed that more than 9 candidate genes related to the process of converting the L-Trp to form TOL, while about 9 genes associated to degrade the large part of external L-Trp as the carbon or energy source. Compared with controls,L-Trp-treated filtrates had a larger amount of 15-ADON production at 24 hrs time point.In summary, cultivating the wheat varieties with high quality, high yield, resistance to pests, and spraying high concentration of auxin or IAN would be an effective way to control S.avenae and FHB.