Effect of solute stress and temperature on growth rate and TRI5 gene expression using real time RT-PCR in Fusarium graminearum from Spanish wheat.

The objective of this work was to study the effect of ecophysiological factors on trichothecene gene expression and growth in Fusarium graminearum. The effect of non-ionic solute water potentials and temperature was examined on in vitro mycelial growth rates and on expression of the TRI5 gene, involved in trichothecene biosynthesis, quantified by real time RT-PCR. This study showed optimal values of 25 degrees C and -2.8MPa (0.982a(w)) for growth. Marginal temperatures such as 15 degrees C and 30-35 degrees C, particularly in combination with water potentials below -2.8MPa, drastically reduced growth. The expression of TRI5 was reasonably constant although some induction was observed between 20 and 30 degrees C, the most favourable temperatures for growth, depending on the water potential imposed, particularly at -7.0MPa. A temporal kinetic experiment at 25 degrees C examined the effect of ionic solute stress on TRI5 gene expression and growth rate. The results indicated independence of growth rate and TRI5 expression, as the fungal biomass increased with time while the gene expression remained constant. This suggested that favourable conditions for growth will result in higher trichothecene production, and that toxin production would always accompany the colonization process at a steady rate while the conditions for growth are permissive. Quantification of key biosynthetic toxin genes by real time RT-PCR was shown to be a valuable tool to gain knowledge of the ecophysiological basis for trichothecene biosynthesis and enable better control strategies to be developed during the life cycle of this important mycotoxigenic pathogen of cereals.