Growth Hormones and the Creeping Thistle Rust

Abstract

A re-examination of the life cycle of the rust fungus Puccinia punctiformis (Str.) Rohl. (syn. P. suaveolens (Pers.) Rostr., P. obtegens Tul. ex Fuckel) on the creeping thistle Cirsium arvense (L) Scop, has led to the development of a method for growing comparable healthy and diseased thistle plants in the greenhouse. These were used to define the developmental changes which result from systemic infection. Closely similar changes are produced by the exogenous application of gibberellic acid (GA3). The endogenous gibberellin content of systemically diseased thistle plants is consistently higher than that of healthy plants during the earlier part of the season when they are growing faster. Evidence is given for the presence of two gibberellins whose relative proportions change during development. The first has not been characterized but there is some evidence that the second may be GA3. These results support the hypothesis that some of the characteristic features of systemic infection of the host are due to the excess production of gibberellins.