Studies On Genotypic Difference In Nitrogen Use Efficiency Among Tibetan Wild And Cultivated Barleys

Tibetan annual wild barley is one of the ancesters of the cultivated barley and is rich in genetic diversity. Besides, it can adapt to various stresses for living in poor environment. In this study, we used Tibetan annual wild barley to determine genotypic variation of low-N stress tolerance and its physiological mechanism, in order to provide some informance for barley breeding and production. The main results were as follows:1. There was a wide variation among wild barley accessions in low-N tolerance. The tolerance of 82 wild barley and 16 cultivated genotypes were evaluated in terms of relative shoot dry weight under 0.4 mmol/L low-N stress and normal N level. The results showed that the germplasms could be divided into three types:low-N tolerant, low-N sensitive and moderately tolerant. Further,7 wild barley,4 tolerant (XZ12, XZ113, XZ103 and XZ149), 2 moderately tolerant (XZ75 and XZ12) and 1 sensitive (XZ56), and 2 cultivated genotypes, 1 tolerant (ZD9) and 1 sensitive (B1130), were selected to analyze the low-N tolerance exposed to 0.2 mmol/L N stress. The results indicated that XZ113, XZ149 and ZD9 exhibited higher relative shoot dry weight (RSDW), while others had lower RSDW.2. The population structure and linkage disequilibrium were analyzed for the 82 wild barley using 789 DArT markers covering the whole genome. The results showed that this natural population can be divided into 3 subgroups. The distance of the whole genome LD extension was analyzed and it differed between different chromosomes. Furthermore, the whole genome association analysis was done in TASSEL and 22 sites were detected (p<0.01). Among them,5 sites were consistent with RSDW, and there were 5,7 and 5 sites that were consistent with those of SNC, SNA and NUE under 0.4 mmol/L N stress. When p<0.001 was used, only 2 sites, bPb-5191 and bPb-5489, were detected on 2H chromosome, and they can explain 22.7% and 21.9% of the phenotypic variation, respectively.3. The nitrate uptake kinetics differed dramatically among 4 genotypes, with XZ149 having the lowest Vmax and Km values, and XZ113 having the highest Vmax and Km values. Besides, photosynthsis (Pn), stomatal conductance (Sc), transpiration rate (Tr), chlorophyll content, soluble protein and NRA contents increased with the increasd N level. Moreover, N concentration can change root morphology and all genotypes used in this study showed the same trend. When N was insufficient, the maximum root length, total root length, root surface area and volume increased so as to obtain more nutrition from environment. When N concentration reached 0.4 mmol/L, these parameters became the largest, and then declined with further increase of N level.