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The Genetic Composition of Gaeumannomyces Graminis Var. Tritici and Control of Wheat Take-All

Author: ChenHuaiGu
Tutor: WangJinSheng
School: Nanjing Agricultural College
Course: Plant Pathology
Keywords: Gaeumannomyces graminis var. tritici Genotype Virulence Simplesequence repeats (SSRs) Fungicide
CLC: S435.121.49
Type: PhD thesis
Year: 2012
Downloads: 28
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Abstract


The incidence of take-all caused by Gaeumannomyces graminis var. tritici (Ggt) and sharp eyespot caused by Rhizoctonia cerealis has been increasing in wheat growing areas of Huang-Huai and lower reaches of Yangtze river and becoming the important diseases of wheat recently. In order to predict and control the occurrence of wheat take-all, it is necessary to understand the genetic structure of the pathogen and the trend of population structure changes. It is also urgently needed to find the effective fungicides and other measures to prevent the disease.In the present study,104isolates of G graminis collected from Henan, Shandong, Anhui, and Jiangsu province in Huang-Huai wheat growing area were identified by amplifying the genomic DNA with two specific primers GGT-RP:NS5and GGA-RP:NS5, respectively. The results showed that all the isolates were G graminis var. tritici (Ggt) genotype. ITS sequencing was the most reliable method to analyze Ggt genotype. All tested isolates were distributed into two main genetic groups, named as Q1and Q2, respectively. Both of which were different from any isolates out of China. The genetic frequency in Q1was higher than that of in Q2. Q1/Q2frequencies in Henan province were different during2years. What resulted in the diffenence of Q1/Q2frequency in Henan province needs further study.To determine the virulence of Gaeumannomyces graminis isolates, three inoculation and two investigation methods were compared. The results suggested that the method with fungal-colonized agar plugs2cm below the wheat seeds combined with the0-6disease grade standard was better than the others, which presented appropriate disease severity and less standard error. The virulence of104G. graminis isolates collected from Henan, Jiangsu, Anhui, and Shandong province in2010and2011was then tested using the method mentioned above. The results showed that the virulence was different significantly among the isolates. There is no significant difference on virulence between populations collected from different provinces. The virulence between genotypes Q1and Q2has also no significant difference.Base on the public genome database, we examined the SSRs in the completely sequenced G. graminis var. tritici genome. The occurrences, relative abundance, relative density, the commonest, and the longest SSRs were analyzed, and compared with other plant pathogenic fungal species:Magnaporthe oryzae and M. poae. The results revealed that the SSRs were abundant in these three genomes, total of13221,9977and11422respectively. In the gene sequences, the Di-, Tetra-and Pentanucleotide repeats were less abundant than in the total genome sequences, while the Tri-and Hexanucleotide repeats were more abundant than in the total genome sequences. In the G. graminis var. tritici genome sequence, Di-, Tri-, Tetra-, Penta-and Hexanucleotide repeats were more abundant than the same repeats in M. oryzae and M. poae genome sequences, indicated that the G. graminis var. tritici maybe is a species with more genetic diversity. The analysis in this study provided new information that could be useful for a variety of applications in population genetics of G. graminis var. tritici.For analysis of genetic diversity and genetic structure of the take-all pathogen, based on the analysis of simple sequence repeats in genomes of Gaeumannomyces graminis var. tritici, we isolated longer SSR motifs of different repeat types and designed17primers for screening. Four SSRs markers with reproducible patterns and diversity between different Ggt isolates were developed. Their usefulness for gentic analysis was assessed on52isolates collected in2010from Huang-Huai wheat growing areas. Four markers displayed each from2to7alleles, with an average of5alleles per locus. Phylogenetic analysis based on these markers showed that55isolates could be clustered into2large clusters. Jiangsu population showed the highest level of genetic diversity, followed by Shandong, Henan and Anhui population.84%genetic variance was within populations. The gene flow (Nm) among populations was2.604.The genetic identities between Anhui and Shandong population was the highest.In order to screening the effective and safe fungicides for the control of wheat take-all, the inhibitory activity of different fungicides in vitro against the pathogen Gaeumammomyces graminis causing wheat take-all was tested, and control efficacy and safety of fungicides at different concentrations were also investigated in pot experiments. In vitro, sterol demethylation inhibitors fungicides (DMIs) exhibited better inhibitory activity in hypha growth of G. graminis, and the EC50values of fluquinconazole, flusilazole, riadimenol, prochloraz, tebuconazole and difenoconazole were0.03,0.03,0.06,0.07, 0.10and0.24mg/L, respectively. The results of pot experiments indicated that silthiopham and difenoconazole exhibited good control efficacy in controlling wheat take-all, and did not affect the emergence and height of seedlings. The control efficiency of fludloxonll was similar to that of difenoconazole, but slightly inhibited the emergence of seedling. The others also provided good control efficacy, but significantly inhibited the growth of the wheat seedlings. Taken together with the aspects of safety to wheat and resistance management, silthiopham, difenoconazole and fludloxonll were considered suitable for the control of wheat take-all, and should be used alternatively.Wheat sharp eyespot caused by Rhizoctonia cerealis is one of the main diseases in the lower reaches of the Yangtze River, where rice-wheat rotation has been adopted. To assess the effect of rice straw mulching on changes of antagonistic bacteria and the incidence of wheat sharp eyespot, a multi-year field study was performed to compare unmulched plots and plots mulched with rice straw for two or three years. Bacterial and fungal populations were evaluated in the cultures prepared from the wheat rhizosphere and bulk soil. Rice straw mulching increased the number of pseudomonas colony forming units (cfu) in wheat rhizosphere and bulk soil. The proportion of total bacteria that were fluorescent pseudomonads was higher in mulched than in unmulched soil. Bacterial isolates antagonistic to R. cerealis were identified using an inhibition zone test. A series of these isolates were typed by partial sequencing of the16S rRNA gene. Pseudomonads had higher antagonistic activity against R. cerealis than other species, and more than80%of rhizosphere fluorescent pseudomonads were antagonistic to R. cerealis. The disease indices in the mulched plots were lower than in the unmulched control. These suggest that rice straw mulching in a rice-wheat rotation increases the number of fluorescent pseudomonads. Additionally, these fluorescent pseudomonads may contribute to the control of wheat sharp eyespot.

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CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Crop pests and diseases and their prevention > Cereal crop pests and diseases > Wheat pests and diseases > Disease > Transgression ( pass ) an infectious agent harmful > Other infectious diseases
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