Anatomic effects of corky bark virus in Vitis

This paper reports on a study of the causes behind the drastic effects of corky bark disease on LN-33. An anatomical study revealed that corky bark virus probably influences the functions of the vascular and cork cambia. The first symptoms of corky bark appear in the vascular cambial zone. Certain derivatives of the vascular cambium do not differentiate into cells which become lignified, either to the phloem or xylem side. The production of cells toward the xylem side is drastically reduced, while an abnormal amount of secondary phloem is produced. The phloem contains sieve-tube-like cells, but these cells occur in narrow bands between abnormally wide rays. No normal cork is formed, but there is a stimulation of cork-like cells in the region of the phloem where the cork-cambium usually arises. A secondary effect of corky bark is the formation of proliferative tissue in the vascular rays of the cane. The cells of this tissue are irregular in shape and have large nuclei; they divide irregularly and are tumorlike in appearance. These findings indicate that corky bark is probably closely related to wound-tumor virus.