Fusarium Spp. Causing Wheat Crown Rot In Major Winter Wheat Growing Regions Of China And The Function Of Deoxynivalenol On The Infection

Wheat crown rot caused by Fusarium spp. has become more prevalent in China recently. To analyze the structure of the Fusarium spp. causing wheat crown rot in major winter wheat growing regions of China, wheat basal stems showing crown rot symptoms were collected from Jiangsu, Anhui, Henan, Hebei and Shandong province from 2009 to 2013. Totally 175 isolates were selected to analyze the distribution and chemotype composition in different geographic areas. The analysis showed that 123 isolates were F. asiaticum, which were of 3-acetyldeoxynivalenol (3-AcDON) (95) and nivalenol (NIV) type (28). Thirty-seven isolates belonged to F. graminearum species, which were all of 15-AcDON type. Others were F. acuminatum, F. pseudograminearum and F. avenaceum isolates. F. asiaticum species with 3-AcDON type was the predominant pathogen causing crown rot in these 5 provinces.The pathogenicity of 120 F. asiaticum and F. graminearum isolates to wheat crown and heads was tested. The results suggested that isolates of F. asiaticum were more aggressive toward wheat crown and heads than F. graminearum. The isolates of DON chemotype were more aggressive toward wheat than isolates of NIV chemotype, but there was no significant difference between them. We also compared the virulence of the Fusarium head blight (FHB) and crown rot (CR) isolates with the same chemotype. There was no significant difference between the two diseases isolates.Finally, DON content was assayed in grains from inoculated wheat heads. The results of HPLC method showed that CR isolates also produce DON during the infection of wheat heads. The statistical analysis showed that toxin-producing ability of CR isolates was stronger than that of the FHB isolates. The DON chemotype isolates produced higher DON than NIV chemotype isolates. There was huge difference on toxin production between the FHB and CR isolates of 3-AcDON and NIV chemotype. Correlation analysis indicated that there was significant positive correlation between the virulence and DON accumulation of isolates.To characterize CR development, we used the transformant Fg-GFP and real-time quantitative polymerase chain reaction analyses to assess fungal colonization and Tri5, Tri6 gene expression during a timecourse of infection. The infection results indicated that mycelia growth from the inoculation point to the crown was slowly, the delay in visible symptoms during the CR infection may be partly explained by the delayed unregulated of Tri5. To further analyse the correlation between the virulence and DON accumulation, the Tri5-deletion mutants were inoculated at the wheat stem base. Compared with its original wild-type, the transformant isolates produced similar symptoms of CR lesion and necrosis, but with a lower level of CR lesion development. The results suggesting that DON is not necessary for stem colonization by this fungus, but has a role in CR disease.