Screening Wheat (Triticum spp.) Genotypes for Root Length under Contrasting Water Regimes: Potential Sources of Variability for Drought Resistance Breeding

Screening for root traits has been one of the most difficult areas to practise over large number of genotypes. Hydroponic systems enable easy access to roots while high-molecular weight polyethylene glycol (PEG) is used to induce water stress. A total of 838 genotypes were evaluated for root length in a hydroponic trial under PEG-induced stress and non-stress growing conditions. Augmented complete block design with seven blocks and six standard control varieties was used. Root length differences were highly significant (P<0.01) under both stress and non-stress growing conditions among genotypes. Osmotic stress has caused an average reduction of 54% in root length. Among the genotypes, root length ranged from 1.4 to 13.3cm under stress, and 4.4 to 23.3cm under non-stress conditions, respectively. The best control variety for drought resistance was significantly (P<0.05) outperformed by four new entries namely Colotana 296-52, Compare, Santa Elena and Tammarin Rock, while the shortest roots were measured on genotypes Aus 16356, Elia, Camm, Portugal 3, and Sentinel. Differences among ploidy levels, domesticated and wild forms were also significant (P<0.05). Hexaploid wheat showed significantly longer roots in both growing conditions while wild tetraploids showed the shortest roots under stress. There was a change in the ranking of genotypes under the two water regimes, which indicates the difficulty of selecting drought resistant varieties under optimum environments.