Definition - What does Inoculum mean?

Inoculum has several different meanings in biology. In its most general sense, an inocolum is a material used to inoculate some other material or substance, such as soil or compost. Inoculums are essentially live microorganisms, usually fungi. Some types can be added as amendments to benefit/improve soil or compost conditions, while others are harmful to plants.

In a negative sense, the term inoculum can also refer to the part of a pathogen that can cause disease. In other words, it is the portion of the individual pathogen that actually contacts the host.

Inoculum also can refer to a white powdery substance that forms on a plant produced by conidiophores, conidia, and mycelium fungus, which are members of the Erysiphales family and frequently referred to as powdery mildew fungi.

An inoculum is sometimes referred to as an inoculant. The terms are interchangeable.

MaximumYield explains Inoculum

As a pathogen, an inoculum is especially virulent when the host plant is susceptible, the environmental conditions are favorable, and enough inoculum exists to attack the plant. Inoculum can be spread by the wind, insects, rain, or by human disturbances. The inoculum must come into direct contact with the plant’s tissue to cause infection.

An inoculum is considered any part of the pathogen fungus, such as the spore or mycelium. If the inoculum is carried by the wind or some other source into a field and promptly infects the crop then it is called the primary inoculum. However, if the inoculum already exists in the field and is infecting the crop, then it is considered a secondary inoculum.

The secondary inoculum develops symptoms from the primary inoculum. Once symptoms develop from the secondary inoculum, the process is referred to as a secondary infection.

This is the life cycle of the inoculum. The pathogen’s life cycle runs from the time of primary inoculum to secondary inoculum, and on to secondary infection. Without the optimal conditions, the inoculum life cycle will fail and the crop will not become completely infected.

In the case of mychorrizae, a fungal relationship between plant roots and soil, inoculums can be a positive thing. Please see Mycorrhizal Inoculum.

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