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The distribution of Fusarium graminearum and F. asiaticum causing Fusarium head blight of wheat in relation to climate and cropping system.

In the main wheat production area of China (The Huang Huai Plain, HHP), both Fusarium graminearum and F. asiaticum, the causal agents of Fusarium head blight (FHB), are present. We investigated whether the relative prevalence of F. graminearum and F. asiaticum is related to cropping systems and/or climate factors. A total of 1844 Fusarium isolates were obtained from 103 fields of two cropping systems: maize-wheat and rice-wheat rotations. To maximize the differences in climatic conditions, isolates were sampled from the north and south HHP region. Based on the phylogenetic analysis of EF-1α and Tri101sequences, 1207 of the 1844 isolates belonged to F. graminearum, and the remaining 637 isolates belonged to F. asiaticum. The former was predominant in the northern region: 1022 of the 1078 Fusarium isolates in the north were F. graminearum. The latter was predominant in the southern region: 581 of the 766 Fusarium isolates belonging to F. asiaticum. Analysis based on generalised linear modelling, the relative prevalence of the two species was associated more with climatic conditions than with the cropping system. Fusarium graminearum was associated with drier conditions, cooler conditions during the winter but warmer conditions in the infection and grain-colonization period, and with the maize-wheat rotation. The opposite was true for F. asiaticum. Except 15-ADON, the trichothecene chemotype composition of F. asiaticum differed between the two cropping systems. The 3-ADON was more prevalent in the maize-wheat rotation; whereas NIV more prevalent in the rice-wheat rotation. The results also suggested that environmental conditions in the overwintering period appeared to be more important than that in the infection and grain-colonization and pre-anthesis sporulation periods in affecting the relative prevalence of F. graminearum and F. asiaticum. More research is needed to study the effect of overwintering conditions on subsequent epidemic in the following spring.