Identification Of Water-Logging Tolerance At Seedling Stage And The Difference Of Photosynthetic Parameters Between Tolerance And Susceptible Types In Brassica Napus L.

Water-logging is often a serious natural disaster in the world. Before 1970,Brassica rapa L. was the main oilseed rape grown in Changjiang River Region in China. At present, Brassica napus L. of domestic widely grown was originally imduced from Europe.lt has the higher yield and disease resistance but less water-logging resistance compared with Brassica rapa L.. The main production areas of oilseed rape-the Middle and Lower regions of Changjiang River has more rain all year round, and the regions is mainly the water-logging cropping following rice especially no-tillage cropping pattern, bring a loss of production. Therefore, breeding for oilseed rape with water-logging tolerance is of great significance for enhancing productivity.The main objectives of this study were:(1) to establish a relatively rapid and accurate procedure of water-logging tolerance,for evaluation the variation of water-logging tolerance among oilseed rape germplasm from different eco-regions in China, and to identify elite accessions with water-logging tolerance; (2) to study the difference of photosynthetic parameters and yield of oilseed rape between water-logging tolerance and susceptible lines in B. napus L.1. Death rate of seedlings was compared in this study under water-logging stress. Results from semi-submergence(water level 3cm above soil surface) and full- submergence (water level totally over the top of seedlings) 2d,4d,6d,7d.treatment showed that the death rate of seedlings observed on the seventh day following the water removed from the cup after the seedlings being full-submerged 6d could be used as a screening criteria for water-logging tolerance. Apllying this method 50 oilseed rape germplasms was pre-screened.3 tolerant and 5 susceptible one were identified from them after water-logging stress. Predictable results from the materials of water-logging tolerant or susceptible known checked with this method indicates the death rate of seedlings observed on the seventh day following the water removed after full-submerged 6d could be usfull methods for identification of water-logging tolerance in oilseed rape.2. Atotal of 634 accessions, composed of 351 domestic one,259 abroad one and 24 unknown source, sampled from different eco-regions, were screened by the method of relative death rate. Results showed that the abroad one performed less tolerant. But the domestic meterials mainly performed tolerance to water-logging. In addition, the accessions of oilseed rape from the Middle and Lower Changjiang River were charecterized with a stronger tolerence to water-logging stress.3. There is no impact found on the thousand seeds weight and the individual plant seed yield when water-logging occurred at seedling stage. However it resulted in a large seeds yield loss when water-logging happened at flowering to pod-seeting period even in a total crop failure of susceptible. The average single plant seed yield of tolerance was only 8% lower than the control while that of susceptible was 34% lower than the control.4. The photosynthetic parameters of leaves of water-logging tolerance and susceptible of oilseed rape was keeping in a same level. but between tolerance and susceptible cultivars, there will be some differences. Their photosynthetic rate was increasing at first and decreasing then after waterlogging treatment compared to CK. Howevr only 2.83 decrease was given to tolerant one and 6.68 decrease found in susceptible one. The transpiration rate in the full waterlogging process remained an upward trend. It was declined at the 16th days of waterlogging of susceptible cultivars which was increasing from 3.02 before waterlogging to 4.34 on the 12th day after the treatment being conducted and then decreased to 4.19 on the 16th day.Transpiration rate of the tolerance cultivars was increasing from 2.62 before waterlogging to 4.30 on the 16th day after the the treatment being conducted. The stomatal conductance and transpiration rate had the same trend. Water use efficiency of tolerant and susceptible were decreasing in the process of waterlogging stress. The water use efficiency of tolerant one was decreasing from 7.61 before waterlogging to 3.93 on the 16th day after the treatment being conducted. While that of susceptible was decreasing from 4.85 before waterlogging to 1.38 on the 16th day after the treatment being conducted. The water use efficiency of the tolerant was significantly higher than the susceptible one.