Investigation of Al-toxicity tolerance in tef (Eragrostis tef) under hydroponic system using root growth measurement and haematoxylin staining methods

Tef is the most widely grown and consumed crop in Ethiopia. The crop is currently gaining growing popularity worldwide as nutritious and gluten free cereal crop. Al-toxicity is one of the factors that limit expansion of the crop worldwide. The aims of this study were to adapt hydroponic system as a phenotyping platform for Al-tolerance studies in tef, to identify appropriate concentration of Al3+ for Al-tolerance screening in tef, and to appraise the use of haematoxylin staining for visual assessment of Al-tolerance in tef. A tolerant and a sensitive genotypes were used to identify appropriate Al concentration. The identified Al concentration was used to evaluate reaction of 28 tef genotypes to Al-toxicity. Root and shoot measurements under Al-treated and control solution were used to compute the relative tolerance indexes. Reaction of the tolerant and the sensitive genotypes to haematoxylin staining was assessed by recording intensity of colour development. The result indicate that, among the five levels of AlK(SO4)2.12H2O (0-550 µM), the 150 µM concentration was found to be an appropriate level to discriminate between sensitive and tolerant genotypes of tef. This concentration adequately differentiated 28 tef genotypes with varied sensitivity to Al-toxicity. The visual assessment of selected tolerant and sensitive genotypes treated with 0, 150 and 250 µM AlK(SO4)2 .12H2O showed a differential reaction to haematoxylin staining consistent with the root growth measurement methods. The tolerant E. curvula showed no staining reaction across all the Al levels. The local Al-tolerant tef landrace, Dabo banja, showed a slightly purplish stain only at the highest level of Al. The two sensitive genotypes (E. Pilossa and Holeta Key), however, showed deep purple staining at concentrations of 150 and 250 µM AlK(SO4)2.12H2O. To the best of the authors’ knowledge, this study is the first to report the use of root measurement and root staining methods in evaluation of tef for tolerance to Al-toxicity using hydroponics platform.