Dutch Elm Disease | Cycle | Elm | Root grafts Root grafts Index document Occurrence


    Photo 13:  Grafted roots of U. americana (Courtesy of N. Tisserat, Kansas State University, Manhattan, KS, USA)

    Root grafting in trees refers to morphological interconnections occurring between roots of the same tree (self-root grafting), of different trees of the same species (intraspecific root grafting) or of trees of that belong to different species (interspecific root grafting). Functional root graft connections consist of joined bark phloem, cambium, and xylem derived from two or more previously distinct roots. As a result, the biological processes of the trees involved can be strongly influenced by each of the grafted participants separately (Photo 13 and 14,{[760]}). A grafted group may function as a unit in response to the environment {[746]}. Fusion of two roots at the point of contact may also result in the formation of partial root grafts that show an incomplete unification of the root vascular tissue {[772]}.

    Natural grafts among tree roots occur in four different forms, i.e., intersections, longitudinal grafts, “web grafts”, and “bridge roots” {[759]}. Intersections occur between similar or dissimilar sized roots that cross at angles approaching the perpendicular. Fusion of roots lying parallel and continuous to one another results in the formation of longitudinal grafts. The latter type of graft may have regions of vascular contact varying up to a meter or more. Elms grown in heavy soil produce a fine root mass {[430]}. Due to confinement of the roots in this soil type, duckfoot-like anastomoses of roots can be formed (“web grafts”). Confined root systems providing the opportunity to form “web grafts” also occur where there is a high water table or where trees grow in shallow soil overlying hard clay, bedrock or hardpan. “Bridge roots” typically connect two roots, but do not extend beyond either root. The two roots may originate from the same tree, or from different trees.

Root grafts Root grafts Occurrence Occurrence