Spring air temperature accounts for the bimodal temporal distribution of Septoria tritici epidemics in the winter wheat stands of Luxembourg

摘要

Septoria tritici is the causal agent of leaf blotch in wheat and among the most damaging fungal cerealpathogens in the humid regions of central Europe. The percentage of the leaf area colonized by S. triticiwas recorded weekly between April and July every season between 2004 and 2010. A total of 11 cultivarswith moderate susceptibility [ratings of 4e6 on a 1 (resistant) to 9 (susceptible) scale] were included. Thedisease level was assessed on the upper three leaf layers at 2 locations between 2004 and 2006 and at 3locations between 2007 and 2010. The period between sowing and the point of time, when 50% of theleaf area was necrotized due to colonization by S. tritici (T50) was estimated for each year, site, cultivarand leaf layer by non-linear regression. T50 values followed a bimodal distribution with one maximumat 245 days after sowing (DAS; early epidemics) and one maximum at 270 DAS (late epidemics). Earlyepidemics were preceded by almost constant daily average temperatures of 13.2 0.8 C between 181and 210 DAS. Late epidemics were preceded by an approximately linear increase in temperature from8.7 0.9 to 12.1 0.9 C during the same period of time. Based on these differences, it seems possible topredict whether an early or a late epidemic can be expected at least 35 days before the epidemicoutbreak. Temperature sums calculated with a base temperature of 6.6 C starting at sowing and endingwhen T50 was reached were not significantly different between early and late epidemics (P ¼ 0.73) andaveraged 1721 49 days. Fungicide applications, which resulted into a delay of the epidemic developmentsimilar to the difference between early and late epidemics, resulted in a yield increase between11.7 and 12.6%.Septoria tritici is the causal agent of leaf blotch in wheat and among the most damaging fungal cerealpathogens in the humid regions of central Europe. The percentage of the leaf area colonized by S. triticiwas recorded weekly between April and July every season between 2004 and 2010. A total of 11 cultivarswith moderate susceptibility [ratings of 4e6 on a 1 (resistant) to 9 (susceptible) scale] were included. Thedisease level was assessed on the upper three leaf layers at 2 locations between 2004 and 2006 and at 3locations between 2007 and 2010. The period between sowing and the point of time, when 50% of theleaf area was necrotized due to colonization by S. tritici (T50) was estimated for each year, site, cultivarand leaf layer by non-linear regression. T50 values followed a bimodal distribution with one maximumat 245 days after sowing (DAS; early epidemics) and one maximum at 270 DAS (late epidemics). Earlyepidemics were preceded by almost constant daily average temperatures of 13.2 0.8 C between 181and 210 DAS. Late epidemics were preceded by an approximately linear increase in temperature from8.7 0.9 to 12.1 0.9 C during the same period of time. Based on these differences, it seems possible topredict whether an early or a late epidemic can be expected at least 35 days before the epidemicoutbreak. Temperature sums calculated with a base temperature of 6.6 C starting at sowing and endingwhen T50 was reached were not significantly different between early and late epidemics (P ¼ 0.73) andaveraged 1721 49 days. Fungicide applications, which resulted into a delay of the epidemic developmentsimilar to the difference between early and late epidemics, resulted in a yield increase between11.7 and 12.6%.