Evaluation of Egyptian broomrape weed stress tolerance in tobacco genotypes through various indices of tolerance indices

The Egyptian broomrape [Phelipanche aegyptiaca (Pers.) Pomel.] is a harmful biotic stress factor affecting tobacco production in many regions. To evaluate weed tolerance among different tobacco genotypes, a trial was conducted using a randomized complete block design with 26 genotypes, three replications, under both non-stress and weed-infested conditions. Twenty statistical stress indices and a new index, the Tolerant Identifier Index (TII), were used to assess weed stress tolerance. The TII incorporates both tobacco performance under stress and non-stress conditions, as well as the dry weight of Egyptian broomrape. Weed infestation reduced dry leaf yield by 37%, and 97% of the variability among tolerance indices was explained by the first two principal components (69% and 28%, respectively). Some indices were highly correlated and provided redundant information, so they were excluded. Yield performance under stress and non-stress conditions showed strong correlations with mean-based parameters (arithmetic, harmonic, and geometric means), drought index, corrected stress tolerance index, and TII. Genotypes G4, G9, G19, G22, and G26 were identified as the most tolerant under both conditions, most of which were Virginia and Flue-cured types originating from the USA. Cluster analysis further validated these findings. Combining weed dry weight with stress indices as TII proved effective in identifying tolerant genotypes. The TII reliably distinguished weed-tolerant genotypes by accounting for both weed biomass and tobacco yield under stress and non-stress conditions.