Comparative Anatomical Effects of the Curly-Top and Aster-Yellows Viruses on the Flax Plant

Abstract

1. A study was made comparing the effects of two phloem-limited viruses, curly top and aster yellows, using flax, Linum usitatissimum L., as the host plant. 2. The curly-top virus induces degenerative changes in the phloem of flax similar to those previously reported for sugar beet, tobacco, and tomato. In vegetative shoots degeneration usually occurs after the first sieve tubes differentiate and appears first in cells adjacent to them; these cells show increased chromaticity of cellular contents and hypertrophy. Some of these cells may also divide. The first degenerative changes are rapidly followed by hyperplastic divisions, resulting in the production of numerous short, abnormal, sieve elements. The hyperplastic tissue differs strikingly from normal phloem in number, arrangement, and size of the sieve elements. It eventually collapses, forming internal lacunae of varying dimensions which are filled in by proliferation of adjacent cells. Extraxylary bundles sometimes differentiate within the wound-heali...