Comparative characteristics of root systems and root exudation of synthetic, landrace and modern wheat varieties

Finding ways to increase the wheat adaptation to drought is now considered as a major problem in breeding new varieties of this crop. This study was conducted to evaluate genotypic differences in fundamental root traits which may have effect on wheat adaptation to unfavorable environments, including drought. Three wheat genotypes representing various evolution levels of hexaploid bread wheat ( Triticum aestivum L.) were used: synthetic wheat developed by crossing variety LEUCURUM 84693 of durum wheat ( Triticum durum Desf., genome АВ, Ukraine) with wild Tausch's goat grass ( Aegilops tauschii Coss., genome D, Turkey), landrace of bread wheat Albostan (genome ABD, Turkey, province Nevşehir), and a modern cultivar Karahan (genome ABD, Turkey). The varieties differed in root diameter, shoot biomass and shoot/root ratio. The removal of above ground biomass caused increase in the root length, number of tips, number of forks, number of crosses and shoot/root biomass ratio of synthetic wheat and Albostan, but decreased these parameters in Karahan. Averaged values of ten measured growth parameters of the plants with removed above ground biomass relatively to the control plants were +28 % for synthetic wheat, 0 % for landrace Albostan and -37 % for cultivar Karahan. These results showed a higher ability of synthetic wheat but lower ability of Karahan to recover from cutting stress and to revegetate. For the first time a comparative analysis of root exudation (amino acids, sugars and organic acids) by wheat genotypes having different levels of evolution was performed. It was shown that Karahan was characterized by high exudation of tryptophan (0.05 mg/g dry roots per day), histidine (0.12 mg/g dry roots per day) and phenylalanine (0.45 mg/g dry roots per day). Total amount of sugars (mostly fructose, glucose and maltose) exuded by Karahan was 55 mg/g dry roots per day, that was 5 and 3 times higher as compared to synthetic genotype and Albastan. The quantum of organic acids in exudates of all studied genotypes was approximately similar and amounted to about 1.8 mg/g of dry roots per day. The results suggested low ability of Karahan to control the flow rate of carbohydrates from roots to the environment. We propose that high root exudation of tryptophane (precursor in biosynthesis of auxins) and sugars may result in deficit of these compounds and involved in impaired shoot regeneration of Karahan. The results demonstrated differences in the functioning of the root system of primitive hexaploid wheat (synthetic) compared to landrace and modern cultivated variety. The nature of these differences requires more investigation.