Pathological Mechanism Of Interaction Between Cotinus Coggygria And Verticillium Dahliae

Cotinus coggygria Scop. is an important part of red leaves landscape of Fragrant Hills Park in Beijing, plays a key role in capital ecological landscape construction. But in recent years, severe occurrence of C. coggygria wilt, caused by Verticillium dahliae Kleb., destroyed the red leaves landscape of Fragrant Hills Park and resulted in the deaths of C. coggygria. It has become a major biological disaster and brought about serious impacts on ecological construction and ecological security of Beijing. We systematically studied the histopathological changes of C. coggygria inoculated with Verticillium dahliae. The dynamics of enzyme activity and proteins in C. coggygria tissues were analyzed during induction procedure, providing fundamental information for revealing the pathogenic mechanism of C. coggygria Verticillium wilt and resistance mechanism of its host. Main results are as follows:(1)Histopathological changes of C. coggygria inoculated with Verticillium dahliae were observed by using paraffin sections and optical microscope photography. The results showed that different parts of C. coggygria had different infection levels, leaves was the highest (18.83%), while the lowest branches (6.72%). After inoculation, the elongation zone and mature zones of plants were initially invaded by hyphae, it appeared in the gap of cortex parenchyma cells withinâ… -3cm of the root tip, and went into the root vessels, finally reached leaves through the vessels of stems and branchs.(2)V. dahliae mainly existed in the vessel of xylem in the form of hyphae, which appeared to be discontinuous. In order to prevent the expansion of pathogen during the process, the wall of vessel was thickened, the inside diameter of vessel was decreased by using jelly and tylosis generated in the vessel, or even the vessel was totally blocked. After C. coggygria was affected, the vessel walls, parenchyma cells and cortical cells were thickened, the inclusions of pith, resin canals and secretory cells nearby increased, the jelly appeared in the parenchyma cells and wood rays. Although parts of vessels were blocked with hyphae, jelly and tylosis in different extent, most of the vessels were healthy and could transport water normally. The blocking of vessels would cause plants wilt, but couldn't affect normal activities, so it was not the primary reason of plants wilt.(3)Cotinus coggygria was inoculated with crude toxin isolated from V. dahliae. In the procedure of induction, CAT activity has declined apparently compared with initial level, the activity of Superoxide Dismutase (SOD), Peroxidase (POD) Phenylalanine Ammonialyase (PAL) and Polyphenol Oxidase (PPO) increased, and activity peaks were accompanied.25 kD,27 kD pathogenesis related proteins expressed in the tissues of Cotinus coggygria. Preinduction period, expression level of 33-45 kD,45-66.2 kD increased, and expression level of 20-25 kD declined. At the end period of induction, expression level of all the soluble proteins decreased.