Changes Of Morphological Structure And Physiological Metabolism In Sugarcane After Smut Pathogen Infection

Sugarcane smut is one of the most important diseases in sugarcane. It was induced by Ustilago scitaminea Syd., prevailing globally and causing seriously yield losses in commercial sugarcane production. Guangxi is the dominant sugarcane growing province in China, the leading sugarcane variety ROC22suffers serious smut disease and results in considerable loss in the sugar industry.In this study, at the part of morphological structure, seedcane setts of sugarcane variety ROC22were inoculated by dipping and grown in pots with soil, until it appeared smut whips, and then observed the appearance of sugarcane plants and the ultrastructure of bud cells in sugarcane; At the part of physiological metabolism, sugarcane varieties GT28and ROC22were selected, their settlings were inoculated by syringe, then smut inoculated settlings were assayed by PCR to determine whether settlings were infected by smut pathogen, and enzyme activities and endogenous hormone content of sugarcane settling were investigated. The results were as follows.1. Infection of Ustilago scitaminea Syd. caused changes in appearance and ultrastructure of host sugarcane bud cell. The result indicated that infected sugarcaen plant grew a long whip, and the cane stem was very tiny without economic value. When the main stems had long whips, the lateral buds also were infected and the whips grew out, the leaves were small and yellow. The damage of smut infection on bud tissue is serious, the bud cells were out of shape, and the cell contents disappeared. The cell wall was destructed, many electron dense substances appeared nearby the cell wall, convoluted hypha appeared in cells, and there were some vesicles in the lesioned cells. The cell nucleus and nucleolocentrosome were deformated and disintegrated, the chromatin was not well-distributed on the cell nuclelus and the nucleolocentrosome generated papillas. Most mitochondria were serious injured and disintegrated, and some of their ridges disappeared and became empty.2. After the sugarcane settling was inoculated with Ustilago scitaminea Syd., the leaf samples were taken from both the pathogen inoculation treatment and control for analyses of the activities of POD, SOD, PPO, PAL,(3-1,3-glucanase and chitinase activity, and the contents of IAA, GA, ABA, SA and JA. The result showed that the activities of POD, SOD, PPO, PAL, β-1,3-glucanase and chitinase in the settling leaves were increased in different degrees after the pathogen inoculation treatment. In the same index, the increase was different at different inoculation time, but the change trend was basically the same in the two sugarcane varieties. After inoculation, The activities of POD and SOD in the resistant variety GT28were higher than in the susceptible variety ROC22, the increased rate of POD activity in ROC22was significantly higher than in GT28at3d and5d after inoculation, and the activity of SOD was not significant difference between the two sugarcane varieties ROC22and GT28. The activities of PPO and PAL were higher in the resistant variety GT28than in the susceptible variety ROC22, they showed significantly higher in GT28than in ROC22at their peaks. In short, the activities of POD, SOD, PPO, PAL in the resistant variety GT28were all higher than in the susceptible variety ROC22. The activities of β-1,3-glucanase and chitinase were also increased, but there were no significant differences between the two sugarcane varieties ROC22and GT28.3. The contents of endogenous hormones in the settling leaf were also changed in two sugarcane varities with different resistance after smut infection. The IAA content was increased slightly at the early stage of infection, but it got down later; the ABA content was increased after pathogen inoculation as compared with the control, and the content of IAA and ABA in the susceptible variety ROC22were slightly higher than in the resistant variety GT28. The GA content was decreased and were lower than control, while the SA content was increased after the smut infection, the content of GA and SA in the resistant variety GT28were higher than in the susceptible variety ROC22. That is to say, after inoculation, while compared to the susceptible variety ROC22, the resistant varietiy GT28had lower IAA and ABA content and higher GA and SA content. The JA content was decreased at the early stage of smut infection but then increased at the later stage, and it appeared earlier in GT28than in ROC22at their peaks.The ratio IAA/ABA was decreased after the smut infection as compared with the controls, and it was decreased more in ROC22than in GT28.