The biology of poplar rust in the South Western Cape with special reference to the carbon physiology of the host-biotroph relationship
An investigation of the host-obligate biotroph relationship of a commonly occurring rust fungus in the South Western Cape, Melampsora sp., infecting Populus canescens (Aiton) Sm., was stimulated by the apparently non-harmful effect of the pathogen on its host. The healthy appearance of the infected poplar tree and the lack of morphological changes in the leaves of infected shoots suggested that the rust was a benign obligate biotroph which, in the absence of its alternate hosts, appears to be adapted to a compatible existence with one host. The ready availability of poplar stands in the South Western Cape which are regularly infected with rust provided the opportunity to study the seasonal changes in carbohydrate levels and composition, total nitrogen levels and dry weight in the healthy and rust-infected poplar leaves. Further information was obtained by feeding entire shoots or single leaves of shoots with ¹⁴CO₂, then assessing levels of ¹⁴C-assimilate and following the translocation of ¹⁴C in the healthy and infected host.
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