Temperature effects on the relative abundance of Fusarium species in a model plant–soil ecosystem

To test the hypothesis that climate is a major factor controlling the distribution of Fusarium species in soil, the effect of temperature on propagule density in soil and colonization of roots was determined experimentally. Five Fusarium species were inoculated together into untreated field soil in pots sown with perennial ryegrass. Changes in the density of propagules in soil recoverable by dilution plating and the proportion of roots colonized by each species were monitored over 12 months at three temperature ranges (13–18, 19–24 and 25–30°C). Propagule density of, and colonization of roots by, F. compactum and F. solani was greatest at higher temperatures (25–30°C). Fusarium torulosum demonstrated greatest colonization ability and propagule density in soil at lower temperatures (13–18°C). The propagule density of the cosmopolitan species F. equiseti remained high at all temperatures and this fungus successfully colonized plant roots under all conditions. While F. acuminatum did not compete well against the other species, the propagule density of this fungus was greatest at low temperatures. The differences in community structure resulting from differences in temperature in this model system mimicked those found when natural communities of Fusarium species are compared along climatic gradients.