Analysis On Genotype, Chemotype And Pathogenicity Of Fusarium Graminearium Species Complex In Wheat

Scab or Fusarium head blight (FHB) caused by species of Fusarium is one of the economically devastating disease in wheat, barley, maize and other small grain cereals in the warm and humid regions of the world. Recently, it has outbreaked in more than30countries of five continents in the word. In recent years, with the increasing in global temperature and changing in crop farming systems, FHB has become more and more epidemic in the wheat-growing regions. The economic losses caused by FHB also become more and more serious. FHB not only can reduce grain yield and quality, but also produce variety of mycotoxins that can contaminated cereal grains which pose a serious threat on the health of human beings and livestock.In order to reduce the disease caused by FHB, infected spikes were collected from some wheat-growing regions in our country in2009and2010. Agar dilution lineation separation was applied to sperate single spores and establish a pathogen library. The differentiation in genetype and chemotype of Fusarium graminearum species complex (FGSC) was investigated by identifying the pathogen strains in the library. The phatogenicity of3ADON-,15ADON-and NIV-chemotypes of FGSC was detected by floret inoculation of nine wheat varieties in field. SRAP analysis was used to find sequence characterized amplified region (SCAR) markers to identify different genotypes of the pathogen. The information obtained in this study provided a better understanding of the pathogenicity of FGSC and references for disease management. The main results were as follows.1. Eight hundred and twenty five isolates of the pathogen were collected from the infected spikes in some major wheat-growing regions in China. The results of SCAR analyses showed that phylogentic species of F. asiaticum and F. graminearum were the. major causal agents of FHB in China. It seems that both species have different geographic distributions in the country. Vast majority of F. asiaticum isolates were collected from relatively warmer wheat growing regions. In contrast, F. graminearum was mainly obtained from the relatively cooler regions. The both species were found in the regions of Yangtze River and Huai River where the annual average temperature is suitable for development FGSC. Chemotype identification of the two species show that, there were three kinds of chemotypes of FGSC in China. Different chemotypes of FGSC have different geographic distributions. The NIV-chemotype isolates were the predominant strains in the upper reaches of the Yangtze River and mountain regions. However, the15ADON-chemotype isolates were the predominant strains in northern part of China. In contrast, the stains form the areas Yangtze River and Huai River are complicated, form where all the three chemotypes of strains were found.2. The pathogenicity of3ADON-,15ADON-and NIV-chemotypes of FGSC was detected by floret inoculation of nine wheat varieties in field. The results showed that the pathogenicity of the three types of strians was significantly different. The3ADON isolates exhibited a stronger pathogenicity than the15ADON isolates which in turn is stronger than the NIV isolates. The FHB resistance of nine wheat varieties was also significantly different. The variety Sumai3revealed the strongest resistance to FHB in all the wheat varieties tested, and the variety Ningmai11was very susceptible to FHB. The scab resistance of other tested wheat varieties was found between the two varieties.3. Ninety-nine pairs of SRAP primers were used on screen the representative isolates of F. asiaticum-NIV, F. asiaticum-3ADON and F. graminearum-15ADON to find species-specific and chemotype-specific markers. Three species-specific SRAP markers was obtained by cloning and sequencing the specific fragments. Three SCAR markers were designed based on the sequences of these species-specific fragments. The SCAR primers specific for F.asiaticum and F. graminearum were verified with72isolates, which showed the two species were well identified. The results indicated that the primer pair mel/em2-172could amplify a172bp PCR product only in F. asiaticum isolates, while the primer pairs of mel/em6-311and me9/em4-639could amplify311bp and639bp PCR products only in F. graminearum isolates.