Response of vessel features to witches’‐broom disease in Zizyphus Jujuba branches

Abstract

It is well‐known that the witches’‐broom disease (WBD) has affected the physiology and biochemistry of Zizyphus Jujuba branches; however, the detailed impacts on the vessel, an important water‐conducting unit of the branches, are not well understood. Investigations were performed to determine whether the vessels in primary branches and secondary branches of Z. Jujuba with WBD were mutated. The sapwood of the branches was examined to quantify variations of the vessel features (including the size, shape, proportion and grouping pattern of vessels) closely related to water transport. In comparison to healthy branches, diseased branches showed significantly shorter, smaller vessels and decreased lumen diameters; but, they displayed increased frequency and wall to lumen ratio of vessels. There were significant interactive effects of branch level and WBD on vessel features. Under the stress of WBD, secondary branches showed significantly smaller tangential diameters, larger frequency and larger wall to lumen ratio of vessels than primary branches. It is proposed that the response of vessel features to WBD in Z. Jujuba branches may be due to a developmental process, which allows the diseased tree to maintain an optimal hydraulic architecture as possible. However, a decreased proportion of vessels may be one cause of the death of the tree.