Xylem development and function in the grape peduncle: Relations to bunch stem necrosis

Using a simple flow test evidence is provided that in some grape varieties xylem development is suppressed just distal to each node of the peduncle system. A little further along, development is again normal giving a bottleneck appearance. The bottleneck would appear to offer a high resistance to xylem sap flow both because of its reduced area of cross-section and because of its having only small, primary vessels. The varieties exhibiting a distinct bottleneck tend to be those susceptible to bunch stem necrosis whereas the ones without it tend not to be susceptible