Morphology and ways of multiplication of some of the groups of plant pathogens

Morphology and ways of multiplication of some of the groups of plant pathogens

6. Overwintering or oversummering (overseasoning) of the pathogen.

6. Overwintering or oversummering (overseasoning) of the pathogen. Overwintering is the process by which some organisms/pathogen pass through adverse conditions which make normal activity or even survival difficult or near impossible. Fungi have evolved a great variety of mechanisms for persisting between crops.

On perennial plants, fungi overwinter as mycelium in diseased tissues, e.g., cankers, and as spores at or near the infected surface of the plant or on the bud scales. Fungi affecting leaves or fruits of deciduous trees usually overwinter as mycelium or spores on fallen, infected leaves or fruits or on the bud scales.

Fungi affecting annual plants usually survive the winter or summer as mycelium in infected plant debris,

Fungi affecting annual plants usually survive the winter or summer as mycelium in infected plant debris, as resting or other spores and as sclerotia (hard masses of mycelium) in infected plant debris or in the soil, and as mycelium, spores, or sclerotia in or on seeds and other propagative organs, such as tubers.

Some plant pathogenic oomycetes (e.g., Pythium) and fungi (e.g., Fusarium, Rhizoctonia) are soil inhabitants, i.e., they are able to survive indefinitely as saprophytes. Soil inhabitants are generally unspecialized parasites that have a wide host range. Other fungi are soil transients, i.e., they are rather specialized parasites that generally live in close association with their host but may survive in the soil for relatively short periods of time as hardy spores or as saprophytes.

Also, some fungi infect cultivated or wild perennial, as well as annual, plants and move from the perennial to the annual ones each growth season. Some rust fungi infect alternately an annual and a perennial host, and the fungus goes from the one to the other host and overwinters in the perennial host.

Bacteria overwinter/oversummer as bacteria in essentially the same ways like fungi, i.e., in infected pla

Bacteria overwinter/oversummer as bacteria in essentially the same ways like fungi, i.e., in infected plants, seeds, and tubers, in infected plant debris, and, for some, in the soil.

Bacteria survive poorly when present in small numbers and free in the soil but survive well when masses of them are embedded in the hardened, slimy polysaccharides that usually surround them. Some bacteria also overwinter within the bodies of their insect vectors.

Viruses, viroids, mollicutes, fastidious bacteria, and protozoa survive only in living plant tissues such as the tops and roots of perennial plants, the roots of perennial plants that die to the soil line in the winter or summer, vegetative propagating organs, and the seeds of some hosts. A few viruses survive within their insect vectors, and some viruses and viroids may survive on contaminated tools and in infected plant debris.

Nematodes

Nematodes Nematodes usually overwinter or oversummer as eggs in the soil and as eggs or nematodes in plant roots or in plant debris. Some nematodes produce juvenile stages or adults that can remain dormant in seeds or on bulbs for many months or years. Finally, parasitic higher plants survive either as seeds, usually in the soil, or as their infective vegetative form on their host.

Forms and locations of survival of fungi and bacteria between crops

Forms and locations of survival of fungi and bacteria between crops

Disease cycle

Disease cycle A series of more or less distinct events occurs in succession and leads to the development and perpetuation of the disease and the pathogen in every infectious disease. This chain of events is called a disease cycle.

A disease cycle sometimes corresponds fairly closely to the life cycle of the pathogen, but it refers primarily to the appearance, development, and perpetuation of the disease as a function of the pathogen rather than to the pathogen itself. The disease cycle involves changes in the plant and its symptoms as well as those in the pathogen and spans periods within a growing season and from one growing season to the next.

Stages in development of a disease cycle

Stages in development of a disease cycle