Genetic variation for salt and zinc defficiency tolerance in aegilops tauschii

Official URL: http://192.168.1.20/record=b1225687 (Table of Contents)

Salinity is a major agricultural problem limiting crop yield, particularly in arid and semi-arid regions where cereal production is common. Water and mineral nutrient uptakes in plants are affected by salt stress, and consequently, plant growth rate is reduced. In arid and semi-arid regions, zinc (Zn) deficiency is also a common constraint to crop production. Among number of solutions to these problems, selection of new genotypes with high tolerance to salt toxicity and Zn deficiency is the most sustainable and widely accepted approach. It is well known that the cultivated (modern) wheat has less genetic variation for a given trait than the wild or primitive wheats. Aegilops tauschii is a wild relative of wheat and the D-genome donor of wheat. In the present MSc study, salt tolerance and Zn efficiency (tolerance to Zn deficiency) of different Aegilops tauschii genotypes and modern wheat cultivars were investigated to identify and characterize the salt tolerant and Zn-efficient genotypes. Experiments were conducted under greenhouse conditions by growing 116 Aegilops tauschii genotypes and 28 cultivated (modern) wheat cultivars at different levels of salt and Zn treatments. Genotypes were tested for severity of leaf symptoms, shoot dry weight, shoot Na, K, Ca and Zn concentrations, and ratios of K/Na and Ca/Na in shoot to determine physiological parameters associated with salt tolerance of genotypes. There was a large genetic variation in tolerance to NaCl toxicity among Aegilops tauschii genotypes based on the severity of leaf symptoms (leaf chlorosis and necrosis) and decreases in shoot dry matter production. This genetic variation has been evaluated and discussed in relation to the shoot concentrations of Na, K, and Ca and K/Na and Ca/Na ratios of the genotypes. The results indicated that K/Na and Ca/Na ratios are very important parameters involved in differential expression of high salt tolerance among Aegilops tauschii genotypes. The Aegilops tauschii genotypes tested for salt tolerance was also examined for their Zn deficiency tolerance. The results obtained showed existence of a marked genetic variation in tolerance to Zn deficiency among the Aegilops tauschii genotypes. The selected genotypes for differential tolerance to Zn deficiency have been characterized for shoot concentrations of Zn, Na, K, Ca and P and also for dry matter production and seed concentrations of Zn. Adequate Zn supply was affective in reducing Na concentrations and increasing K/Na ratio of plants. The results of this thesis revealed new Aegilops tauschii genotypes with very high tolerance to both Zn deficiency and NaCl toxicity. These genotypes have been recommended for exploitation in future breeding programmes.