Managing Difficult Plant Diseases: Inoculum is microscopic

Rose black spot disease occurs only on genetically susceptible roses when there are periods of leaf wetness long enough for infection to take place. Photo courtesy James Chatfield

By James Chatfield, Joseph Boggs, and Erik Draper

Inoculum is the structure or part of the pathogen that initiates disease. Microscopic, it can take the form of:
● spores or threadlike mycelia of fungi;
● bacterial cells;
● parasitic eelworms known as plant parasitic nematodes; or
● submicroscopic particles of viruses or phytoplasmas—so small even regular light microscopes cannot detect them.

One of the reasons infectious plant diseases were mysterious for so long, and why disease management is complicated, is the inoculum of the pathogen is invisible to the naked eye when it arrives at the plant, where it then penetrates and infects the plant tissue. Green industry professionals consider insects and mites to be small and hard to see, but they are gargantuan compared to virulent plant pathogens that cause infectious plant disease, along with the other two components of the disease triangle—‘the susceptible host’ and the ‘environment conducive to disease.’

Read the full article: Managing Difficult Plant Diseases

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