THE RELATION OF BARK MOISTURE TO THE DEVELOPMENT OF CANKER DISEASES CAUSED BY NATIVE, FACULTATIVE PARASITES: V. ROOTING BEHAVIOR AND DISEASE VULNERABILITY IN CUTTINGS OF POPULUS TRICHOCARPA TORREY AND GRAY, AND P. 'ROBUSTA'

Abstract

In cuttings from 1-year-old shoots of Populus trichocarpa Torrey and Gray and P. 'robusta', correlations were found to exist between the degree of vigor as expressed by the production of basal callus and the associated wound roots, and the relative turgidity of the bark at the time of harvest or planting. The ability to produce basal callus and wound roots decreased in cuttings with relative turgidities below the 80% level, and many were killed by the development of basal cankers caused by Fusarium lateritium Nees and Cytospora chrysosperma. (Pers.) Fr. Therefore, the bark moisture level in cuttings was indicative of their ability to produce basal callus and wound roots in addition to their vulnerability to these canker diseases caused by facultative parasites.In uniform-sized cuttings of P. 'robusta' no relation was found between the production of morphological roots developing from root primordia, and the bark moisture level, or the percentage of plants which survived. Larger numbers of morphological roots developed on cuttings from the basal and, consequently, older parts of stems.The production of basal callus and wound roots in P. 'robusta' was found to be related to the total weight of cuttings of uniform size, which suggested that weight determinations in the field may provide useful guides into the general level of vigor of dormant nursery stock and stored material.