Global distribution of Fusarium graminearum, F-asiaticum and F-boothii from wheat in relation to climate

Species of Fusarium that have been segregated from F. graminearum have restricted geographic ranges and it has been suggested that this is due to climate, especially for F. asiaticum. Climate envelope modelling with BIOCLIM was used to quantify the differences in climatic range for F. graminearum, F. asiaticum and F. boothii on wheat. A second analysis used eight climate parameters calculated for the month in which anthesis is likely to occur. Published records were used as data, subject to criteria for precise identification and georeferencing. There were significant differences between species in the ranges of most climate parameters used in the modelling. F. graminearum was recorded from all continents except Antarctica and its predicted distribution included most major rainfed wheat-growing regions of the world, except for the hottest areas of south Asia. There appeared to be few climatic limits on the distribution of F. graminearum on wheat. The restricted distribution of F. asiaticum, principally in east Asia, was confirmed. BIOCLIM analysis indicated that F. asiaticum occurred in areas, where the warmest quarter had mean temperatures > 22 A degrees C and rainfall > 320 mm, rather than areas with high mean annual temperatures as previously had been suggested. F. boothii was recorded from relatively few, widely scattered locations, mostly in Africa and Mexico, which tended to be warm, with lower seasonality of temperature, higher seasonality of precipitation and drier conditions at anthesis than the other two species. Areas of the world predicted to have suitable climate at anthesis for F. asiaticum and F. boothii were more extensive than their recorded distributions or those predicted by BIOCLIM, suggesting that climatic constraints on these species were acting principally at stages of the life cycle other than infection of wheat heads. There is a need for more comparative studies of these species over the whole disease cycle to establish at which stages climate is limiting.