Assessing resistance to Septoria tritici blotch in a multi-parent advanced generation inter-cross (MAGIC) population of wheat (Triticum aestivum L.)

Septoria tritici blotch (STB) caused by Zymoseptoria tritici, is the most economically important fungal disease of wheat in the UK⁽¹⁾. STB has been estimated to cause an annual economic loss of £100-200M in the UK and costs wheat growers an expenditure of about £140-280M per year on fungicides. STB is majorly controlled by using fungicides and resistant cultivars. However, the pathogen rapidly adapts to fungicides and resistant varieties which makes it difficult to control. Thus, there is constant effort to develop new sources of resistance against Z. tritici, one of which is the use of multi-parent advanced generation inter-cross (MAGIC) wheat populations, which allows fine mapping of resistance traits as a result of high level of genetic recombination⁽²⁾. The aim of this study is to conduct accurate measurements of disease incidence and severity of STB using automated image analysis and visual assessment, on a UK MAGIC wheat population. A replicated field experiment using 300 wheat lines was carried out at the University of Reading Crops Research Unit, Sonning. The population was evaluated under natural STB infection at two time points (T1 and T2) separated by 56 days. Result showed that correlation between STB mean incidence at T1 and T2 was weak with r_s = 0.25, p=6.1x10^-6 while heritability values of 0.6866 (T1) and 0.4738 (T2) showed that STB resistance is largely heritable. STB severity measured as the percentage of leaf area covered by lesions ranged from 9.78% to 75.58%. This research will aid quantitative trait loci mapping in order to locate genetic markers correlating with STB resistance, to inform wheat breeding for sustainable STB control.