Anatomic effects of barley yellow dwarf virus and maleic hydrazide on certain Gramineae

Infection with the virus of barley yellow dwarf disease and treatment with maleic hydrazide produce many similar external and internal degenerative changes. These are depression of growth, the yellowing of leaves, the forming of sugary exudate on leaves, and the necrosis of certain tissues, particularly of the phloem. A significant difference exists between the initial effect of the virus and that of maleic hydrazide in the growing parts of shoot and root. Virus injury is first recognized, anatomically, in the young phloem, whereas the first effect of maleic hydrazide is expressed in the inhibition of meristematic activity. The initial derangement in the phloem induced by the virus is of such a nature that the existence of a close relation between the virus and the phloem may be inferred: the virus seems to move in the mature sieve elements. Maleic hydrazide does not appear to be primarily associated with the phloem, but it also probably enters this tissue (the phloem) since in older phloem it induces degenerative changes similar to those found in the yellow dwarf plants.