Another interesting technique, indi

Another interesting technique, indicating crop toleranceunder stress, is simple yield screening. Cuin et al.[63] developed a screening method to indicate wheatsalt tolerance under field conditions. They argued thatalthough some belief in the selection of the most tolerantwheat species, some believe that the use of fieldmethods may not be easy and can be problematic dueto the complexity of the environmental conditions.They also indicated that the evaluation of physiologicaltraits is also dependent on the researcher personality.The authors determined a set of 14 physiological andagronomic factors (using a range of statistical methods)to find a combination with the two following characteristics:(1) easy and rapid measurement, and (2) a highrate of predictability. They found that the combinationof the chlorophyll content (measured in the 5th leaf following6 weeks of salt treatment) and the Kþ content inthe sap of the aerial part, measured simultaneously, is asuitable combination that can be used as an efficienttool for breeding purposes [64,65]. The interestingpoint was the reverse correlation of salt and Kþ contents;indicating that the higher salt stress tolerancewas associated with the less Kþ content [66].Development of suitable screening methods forinvestigating wheat salt tolerance is an important toolin the production of resistant wheat genotypes. A largenumber of wheat genotypes have been used by Zhuet al. [67] for screening wheat salinity tolerance, usingvarious physiological indices. The general contributionof each trait towards salinity tolerance was determinedusing regression equations. Their results indicated thatmost of the bread wheat genotypes had superior abilityto exclude Naþ, resulting in a higher relative wheatgrain yield. The important factors determining wheattolerance to salinity were the ratio of Kþ/Naþ and theKþ content of leaf and xylem tissues, followed by highxylem Kþ content, and high osmotic potential.