ABSTRACT
This chapter concentrates on pathogens of shoot systems, particularly shoots of annual plants, because it is these parasites that have attracted most research on effects on carbon transfer and partitioning. It explains some points of similarity with parasitic angiosperms, concentrating on parasitic fungi, not because they are the most common agents of plant disease, but because they typically parasitize growing higher plants, whereas bacteria often invade mature or detached organs. Most fungi have constitutively expressed transport and metabolic systems for glucose, which is readily utilized as the sole carbon and energy source. Apoplastic movement of carbon has clearly been shown to be important where there is no direct phloem link between source and sink, and in parasitic angiosperms this pathway makes a significant contribution to carbon gain and parasite growth. Effects of pathogens on the pH of the host apoplast influence the role of invertases and local effects on source-sink relationships.
