| Pyropia yezoensis is one of the alges, which has the highest yield value in the world. The annual output value is more than $2 billion alone Japan. South Korea and China. But the laver breeding sea area had suffered from enormous pecuniary loss caused by disease, recently. Till now, lots of studies have been performed from the environmental ecology, etiology, the prevention and monitoring of disease and the P. yezoensis itself. However, there still lack an effective solution to this issue. In this study, based on the previous studies, we have a systematic research on the change of of disease resistance related indexes on the physiological and biochemical level of P. yezoensis coused by Pyt. porphyrae, by analyzing the indicators under the condition of normal and infected by Pythium porphyrae. Then according to the principle of biostatistics, through the principal component analysis, find a comprehensive index which can use to evaluat the red rot disease resistance for P. yezoensis, give a theoretical basis for the screening of the disease resistance strains to Pyt. Porphyrae, and provide the reference to explore the mechanism of disease-resistance for P. yezoensis.1. The determination of disease related indexes on physiological and biochemical levelIn this study, the content of defensive compounds (ROS, Pro), the activity of the protective enzymes (PAL, PPO) and MDA in Pyropia yezoensis gametophyte during the course of infection by Pythium porphyrae at different times (0,1.3,5,7,9 days) were measured. The result indicated that the infection of Pyt. Porphyrae could break the dynamic balance of ROS in cells that leads to its significant increase (P<0.01), and the osmotic balance was broken, Pro content was raised markedly (P<0.01). and the activity of protective enzymes such as PAL. PPO was found to be enhanced appreciably(P<0.01), as a result the cells membrane was damaged, and MDA content was changed. Based on these data, we inferred an outline that defensive compounds and protective enzymes of Pyr. yeozensis respond to Pyt. porphyrae infection as follows:The content of ROS in cells of Pyr. yeozensis would increase while induced by the infection of the pathogen. When the host cells received much ROS, the content of Pro was increased and the activity of PAL and PPO was enhanced indicating that the defensive system and the activity of the protective enzymes were activated, at last the cells membrane of the host were damaged by the excess ROS, lead to the lipid peroxidation of the cells membrane and high MDA levels were recorded. The results provided the fundamental data for understanding the mechanism of red rot disease resistance in P. yezoensis.2. The construction of assessment indexes for disease resisitance of P. yezoensisWe analyzed the change of disease resistance related indexes about physiological and biochemical during the infected by Pyt. Porphyrae in P. yezoensis, correlation analysis revealed that the five biochemical substances(ROS, MDA, Pro, PAL, PPO) and four physiological parameters (NPQ, Qp, Fm/Fv, YII) involved in disease resistance reseach were highly correlated with time during the infected by Pyt. Porphyrae (P<0.01), because of the obvious variation with infection time as well as the wide existence in gametophytic, we chose the disease resistance related indexes for the subsequent analysis, based on the principal component ananlysis, the composite assessment index for disease resistance can ba calculated as follows:Z=0.12*zPro-0.12*zMDA+0.18*zROS+0.24*zPAL+0.19*zPPO+0.14*zFv/Fm +0.17*zYII-0.07*zqP-0.05*zNPQ.3. The relative resistance of P. yezoensis species to infection by Pyt. PorphyraeThe relative resistance among cultivated (mainly in our lab) populations to infection by Pyt. Porphyrae was investigated. Resistance was assessed by exposing the isolates to equivalent amounts of infective material (zoospores) and measuring the disease resitance related parameters and disease index. The cultivated strains PYL-349 and PYL-348 of P. yezoemis were highly susceptible to the infection of Pyt. Porphyrae with the comprehensive assessment indexes of -0.94 and -0.36, respectively. The cultivated PYC200912-74 were relatively resistant with the comprehensive assessment index of 1.10. And displayed a fewer infection sites, a less infected thallus areas and smaller disease indexes.The result shows that there is a significant differences between different strains, and we can take advantage of the strains screening in different disease resistance as the material of breeding. The conclusions can establish physiological and biochemical characters for selecting resistant sources, provide theoretical basis for disease control and resistant breeding for P. yezoensis. |
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