Huixianhong,a susceptible wheat variety to stripe rust, wasinoculated with CY-29 (vivulent) in field. Diurnal transpiration changes of diseased flag leaves were measured with LI 6200 Photosynthetic System. Leaves with low severity(5%) were similar to healthy leaves in diurnal changes of transpiration. Transpiration rate (Tp) showed a sharp curve of single peak with the maximum value in 10∶00-12∶00, and decreased greatly in mid-day. Rapid increases in leaf diffusive resistance (LDR) and quick decreases in stomatal conductance (Gs) in mid-day were observed. There were no obvious changes in relative water content(RWC) to compared with healthy leaves. Their water losses through transpiration was still under control. Diurnal transpiration changes of leaves with medium severity (40%) or high severity (80%) were obviously different from the healthy leaves. Their Tp increased greatly before noon, with the maximum at 12∶00 and was kept in a higher level in the whole day, compaired with high Gs. Their RWC lowered significantly in 10∶00-16∶00.Flag leaves with medium and high severity lost their ability to control water losses and their water balance was seriously disturbed.%以条中29号小种(CY-29)诱发接种小麦感病品种辉县红，采用LI-6200型光合系统仪对小麦发病旗叶蒸腾作用的日变化进行监测。结果表明，不同严重度小麦病叶蒸腾作用的日变化明显不同。轻度病叶(严重度为5%)蒸腾作用的日变化趋势与健叶接近，蒸腾速率(Tp)表现出以上午10∶00～12∶00时为最大值的单峰曲线，午后剧烈降低；气孔导度(Gs)在上午10∶00时达全天最大值，之后迅速降至低水平；叶片扩散阻力(LDR)在午前稳定在较低水平，午后迅速升高，16∶00时达全天最大值；与健叶相比，轻度病叶相对含水量(RWC)未发生明显的变化，仍可有效控制水分的蒸腾散失。中度病叶(严重度为40%)和重度病叶(严重度为80%)蒸腾作用的日变化与健叶明显不同，病叶蒸腾速率在午前大幅升高，至12∶00时达全天最大值，午后一直维持很高的蒸腾水平；病叶在全天保持很高的气孔导度，组织相对含水量在午后大幅降低，完全失去了控制水分散失的能力，水分平衡受到了严重的破坏。
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