Organisms that cause plant disease: their detection, identification and proof of their role as pathogens

Abstract

The range of organisms responsible for plant disease is vast and extends from the higher plants themselves, the parasitic angiosperms, to submicroscopic segments of naked RNA, the viroids. Between these extremes of size, one may find plant pathogenic organisms among the fungi, nematodes, protozoa, algae, bacteria, actinomycetes, mycoplasmas and viruses. In addition, components of the abiotic environment may interact with infectious organisms, causing qualitative and quantitative changes in disease symptoms and often resulting in greater crop losses. Also, two or more components of the biotic environment may interact in mixed infections. Again such interactions may result in more severe symptoms, but in some cases prior inoculation with a less virulent parasite may induce resistance to a more virulent one. Indeed this phenomenon, termed cross-protection, has been used as a successful control measure (section 12.6.4).

The correct diagnosis of any disease is a prerequisite of control.

(N. W. Schaad, 1979)