Identifying traits leading to tolerance of wheat to Septoria tritici blotch

- Crop traits and yield loss caused by Septoria were studied over a large dataset of field trials.
- Yield correlated to sink traits in treated crops, and to source traits in untreated crops.
- Yield losses were proportional to senescence advance and HAD reduction, and correlated to grain weight decrease.
- Senescence earliness, grain weight, and canopy extent parameters of treated crops modified disease tolerance.

Identifying tolerance traits to diseases in wheat genotypes has an increased interest to minimize pesticide use and to complement resistance and escape.Yield tolerance to Septoria tritici blotch (STB) was studied pooling up three experiments involving 18 genotypes, 5 years and 6 sites in France, amounting to 161 genotype × year × site × management combinations. Each combination involves a crop pair (treated or not against foliar diseases) repeated two to three times. Most crops were grown under high fertilization, and STB was the main disease present in untreated crops. Crop traits (ear density, grain number and weight, area of leaf laminas) were recorded; green area of leaf laminas over time was fitted to a Gompertz equation, producing metrics for senescence traits (time and duration).Over the whole dataset, LAI from 1.1 to 7.5 m2 m−2; yields from 280 to 1122 gDM m−2 and relative yield losses up to 70% were recorded. Fungicide treated crops exhibited slightly larger ear density and leaf lamina area independently of the intensity of epidemics. As an overall trend, yield became more determined by source traits when epidemics occurred. Yield loss was proportional (r2 = 0.7) to senescence advance by disease. Decrease in grain number and weight were also correlated (r2 = 0.4 and 0.8, respectively) to yield loss. Two epidemic indices were built to compare data across year × site combinations. Then yield in untreated crop was predicted (r2 = 0.87) from yield in corresponding treated crop, and interaction of epidemic indices with traits of the treated crops that therefore were pointed out as responsible for tolerance variability. Late senescing crops exhibited a greater tolerance to epidemics. Conversely, grain weight was a major key of intolerance. To minimize the trade-off between yield potential and tolerance it is thus suggested to maximize grain number.This study represents a first step in identifying key traits involved in tolerance to STB in varying agronomic conditions and cultivars.