Study On Resistance Mechanism Of Soybeans Infected By Phytophthora Sojae

The dynamic changes of morphological and structural differences and biochemical characters of soybean varieties with different resistance to Phytophthora sojae and different ages were systematically investigated before and after inoculation with race 1 of Phytophthora sojae. According to the differences of morphology and structure and the changes of biochemical characters, the mechanism of soybean resistance to Phytophthora sojae was discussed in this paper. The results were as the follows:1 The morphological and structural resistance to Phytophthora sojaeMajor accumulation sites of Phytophthora sojae zoospores were rootlets and meristem and elongation zone of tap roots tips, then encysted, and germinated to primary and secondary hypha. The show of morphological and structural resistance to Phytophthora sojae from macroscopy to microscopy was the root shape of smaller rootlet/tap root: turgescent meristem zone of root tips; changes of cell structure of root and stew.2 The potential biochemical resistance to Phytophthora sojaeThe differences of SOD, P0, PPO, PAL activities and the contents of phenols and flavonoids between resistant and susceptible varieties were not significant(a =0. 05) before inoculation. So, the seedling resistance of soybean to Phytophthora sojae was results of biochemical changes induced by the infection of Phytophthora sojae.The increases of P0 activity and flavonoids content in the roots of susceptible varieties before inoculation were mainly within 14 days after seedling. The activities of SOD, PPO and PAL and the content of phenols were increased with age after 14 days. So, the resistance of older soybean plants to Phytophthora sojae was very correlative to the increase of SOD, PPO, PAL and P0 and the accumulation of phenols and flavonoids during the growth process.3 The biochemical resistance to Phytophthara sojaeThe PAL activity in resistant seedlings roots and leaves, the content of phenols in roots, stems and leaves, the content of flavonoids in leaves after inoculation and that in roots and stems infected after 48 hours, the PAL activityin roots of older susceptible varieties increased in comparison with their contrast plants, while all in the younger susceptible varieties decreased in comparison with their contrast plants after inoculated with race 1 of Phytophthora sojae. The contents of phenols and flavonoids in roots of older susceptible varieties also showed different accumulation and consumption process after inoculation. This proved that metabolic pathway of phenylalanine was very correlative to the resistance, and producing all kinds of secondary metabolic matters was the main defence reaction of soybean to Phytophthora SOjBe.The PPO activity in seedling roots and leaves of resistant varieties increased in comparison with their contrast plants, but the susceptible varieties did not. So, the phenols in resistant varieties could change to more toxical oxidase by phenoloxidase to resist Phytophthora sojae. This was the defence reaction after metabolic pathway of phenylalanine.The activities of P0 and SOD in seedling roots, stems and leaves of resistant and susceptible varieties all increased in comparison with their contrast plants, the increased ranges of SOD activities of resistant varieties were more than those of the susceptible varieties. The activities of P0 and SOD in roots of older susceptible varieties also increased in comparison with their contrast plants at some stage. So, using P0 and SOD to clean excess oxygen radical to avoidinembranous overoxidation was another defence mechanism of soybean to Phytophtbora sojae.Ge xiu梮iuCrop Genetics and BreedingTutor:Rrof. Yang Qing梜ai...