Structure and development of adventitious roots in Salix caprea and S. caprea × S. viminalis

Abstract

Formation and structure of adventitious roots in cuttings of two clones of S. caprea and a hybrid betwen S. caprea and 5. viminalis was studied with light microscopy (LM) and transmission electron microscopy (TEM). The hybrid contained large preformed root primordia, which in cuttings placed in water developed into roots in only three days. One of the S. caprea clones contained minute preformed root primordia, which developed into roots in about eight days. Treatment with indolebutyric acid (IBA) increased the percentage of rooted cuttings and the number of roots formed. Roots emerging from IBA‐treated cuttings contained both mature protophloem and protoxylem, while in roots of untreated cuttings only some sieve elements of the protophloem were mature. In the other 5. caprea clone no preformed root primordia were detected, but after treatment with IBA roots appeared in about two weeks. The cambium in treated stems produced a large number of cells, most of which differentiated into xylem. Root primordia were initiated in the newly produced tissue external to the cambium. The roots contained both mature protophloem and protoxylem at emergence. A few roots emerged also from extensive callus tissues formed external to the basal end of the cuttings. Cell enlargement and cell divisions in various parts of the base of the cuttings caused disruption of the peripheral tissues, which made the cuttings susceptible to infection by microorganisms.