Evaluation Of Barley Germplasm In Waterlogging Tolerance And Physiological Mechanisms Of The Tolerance

Waterlogging can be a problem for many crop productions worldwide. Barley (Hordeum vulgare L.) is relatively sensitive to waterlogging, so the stress will be one of the important limiting factors to barley production in some areas. There are great differences in waterlogging tolerance among plant species and genotypes within a species. Consequently, it is one of the most effective approaches to develop waterlogging tolerant genotypes in improveing crop productivity on the waterlogged areas. However, there is little information about the mechanisms of waterlogging toelrence and the genetic difference in plants, thus exposing a constraint on carrying out relevant breeding and cultivation practices. In the present research, 15 barley genotypes were used according to a previous trial for evaluating waterlogging tolerance among more than 400 barley genotypes. The plants were exposed to waterlogging stress at tillering stage. According to growth performance, 6 genotypes with different waterlogging tolerance were selected for use in further field and laboratory analysis. Meanwhile, the effect of waterlogging on barley growth and the physiological mechanism of genotypic difference in waterlogging tolerance were also examined. The main results are as follows:1. Genotypic difference of yield loss in response to waterloggingFifteen barley genotypes were exposed to waterlogging stress for 12 d at tillering stage to investigate the genotypic difference in yield loss. The results showed that grain yield was significantly reduced under waterlogging, and among three yield components spike number was most affected, followed by grains per spike and grain weight least affected. The reduction in spike number is mainly attributable to few tillers and low effective tillers per plants. The significant differences were detected among the genotypes in their response of yield formation to waterlogging, and local race Yongjiahong Liuleng showed least yield loss, while the two Australian barley varieties had the greatest reduction. The values of direct path coefficients of yield components to yield were in order of spike number, grains per spike and grain weight. The effect of spike number on yield via grain was quite small, and via grain weight was large and positive; effect of grains per spike on yield via spike number was also small and via grain weight was large and negative; effect of grain weight on yield via both spike number and grains per spike was large, but with different direction.2. Genotypic difference of growth inhibition in response to waterloggingLeaf chlorosis index (LCI) is not a best indicator to identify waterlogging tolerance of all barley genotypes, but it is suitable for most genotypes in this study. Length and width of new leaves initiated after waterlogging reduced for all genotypes but 93-3143, which remained little changed under waterlogging. The reduction of leaf size exposed to waterlogging was less than that after the removal of waterlogging. TPP also had the same trend. In comparison with the control, waterlogging caused the reduction of 29.2% and 54.4% in plant height (PH) and shoot dry weight (SDW), respectively, averaged over all genotypes. There was a significant difference in the reduced extent, with Franklin being most reduced.3. Genotypic difference of photosynthesis in response to waterloggingSix barley genotypes, differing in waterlogging tolerence, were selected in the field, to investigated photosynthesis and chlorophyll content in response to waterlogging. The results showed that waterlogging caused a fast decline in net photosynthetic rate (Pn) and stomatal conductance (gs), and little change in chlorophyll content in the early days of treatment, indicating that reduction of photosynthetic rate might be mainly attributed to stomatal closure. With going on of waterlogging, all genotypes did not show further decline in Pn, but Dan 95168 and 93-3143 had an obvious increase. However, SPAD values were significantly decreased in all genotypes. After the removal of waterlogging, waterlogged plants of all genotypes showed, to some extent a gradual increase in gs, and again there was a dramatic difference in the recovery extent among genotypes, Yongjiahong Liuleng and Dan 95168 being the genotypes with the largest and smallest recovery, respectively. Complete recovery was found for all genotypes, but for Franklin, SPAD value was still lower in waterlogged plants than the controls. In addition, the correlations were significant between waterlogging tolerance of barley and the photosysnthesis in the upmost fully expanded leaf on 14 DAR.4. Genotypic difference of malondialdehyde content and antioxidant enzyme activities in respone to waterloggingA dramatic increase in malondialdehyde (MDA) content, and corresponding increase of superoxide dismutase (SOD) and peroxidase (POD) induced by waterlogging in early days of the experiment were found, indicating the occurrence of oxidative stress in barley plants exposed to waterlogging. There was a highly significant difference in the changed extent of all these parameters arisen from waterlogging among genotypes. Franklin and Yongjiahong Liuleng, which were relatively sensitive to waterlogging in terms of growth,...