Mechanisms of attack

Abstract

Pathogens which cause immediate and severe tissue damage to their host plant are conventionally regarded as less specialized parasites which obtain their nutrients from cells killed in advance by metabolic products. Other parasites, perhaps an intermediate group, invade and kill plant cells. Such necrotrophs are in contrast to biotrophs, more specialized parasites which at first have only a slightly adverse effect on the host although the latter is usually more severely damaged when sporulation occurs. These harmful effects are often caused by substances produced by the pathogen, or perhaps by the host as a result of infection, and include enzymes, toxins, growth regulating substances and others. There is an extensive literature on the biochemical and physiological aspects of these substances, and only a brief summary can be given here. General accounts of host/parasite interaction are given by Buxton (1964), Yarwood (1967), Mirocha and Uritani (1967: molecular and biochemical aspects) and Wood (1967).