Identifying traits leading to tolerance of wheat to Septoria tritici blotch
Résumé
tIdentifying tolerance traits to diseases in wheat genotypes has an increased interest to minimize pesticideuse and to complement resistance and escape.Yield tolerance to Septoria tritici blotch (STB) was studied pooling up three experiments involving18 genotypes, 5 years and 6 sites in France, amounting to 161 genotype × year × site × managementcombinations. Each combination involves a crop pair (treated or not against foliar diseases) repeated twoto three times. Most crops were grown under high fertilization, and STB was the main disease present inuntreated 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 senescencetraits (time and duration).Over the whole dataset, LAI from 1.1 to 7.5 m2m−2; yields from 280 to 1122 gDM m−2and relative yieldlosses up to 70% were recorded. Fungicide treated crops exhibited slightly larger ear density and leaf lam-ina area independently of the intensity of epidemics. As an overall trend, yield became more determinedby source traits when epidemics occurred. Yield loss was proportional (r2= 0.7) to senescence advanceby disease. Decrease in grain number and weight were also correlated (r2= 0.4 and 0.8, respectively) toyield loss. Two epidemic indices were built to compare data across year × site combinations. Then yieldin untreated crop was predicted (r2= 0.87) from yield in corresponding treated crop, and interactionof epidemic indices with traits of the treated crops that therefore were pointed out as responsible fortolerance variability. Late senescing crops exhibited a greater tolerance to epidemics. Conversely, grainweight was a major key of intolerance. To minimize the trade-off between yield potential and toleranceit is thus suggested to maximize grain number.This study represents a first step in identifying key traits involved in tolerance to STB in varyingagronomic conditions and cultivars