University:
Michigan State University
Course:
MIC 413 | Virology
Academic year:

2024
Views:

87

Pages:

1
Author:

Vernanda G.

INFECTION CYCLE AND INFECTION CHAIN Sporulation starts from the formation of spore bags, spore formation and spore ripening. Sporulation occurs only in the cells of the host plant and when the spores produced are mature they are ready to be dispersed either actively or passively until they find their host. The location of the host plant can be in the immediate vicinity or very far away, up to hundreds of km. If the spores are still alive and they happen to fall on a suitable host plant along with suitable climatic conditions, infection will occur. These spores are also called dispersed units, starting to grow, called infection units, with germ tubes, appressorium and hyphae for penetration into plant tissue, for example leaves, through stomata or directly penetrating the epidermis of the leaf. Morphologically, each part of the infection unit can be distinguished. Biochemical processes occur from the time the spores begin to germinate. These infectious units cause disease symptoms around the infection which look like spots or patches of various sizes. The symptoms of the disease it causes are unique to each pathogen species. Depending on the species of pathogen that attacks, the symptoms of the disease can be limited only locally around the site of infection, but can also be systemic, that is, covering all parts of the plant. In studying epidemiological developments, if the symptoms are only local, changes in the size of each spot can be measured or the increase in the number of spots can be counted at certain times. So here each spot is considered as one unit. However, if the symptoms of infection are systemic, the entire plant is considered as one unit. From these spots, conidiophores will grow which at the ends produce more conidia. When the conidia are mature, they will be released and carried by the medium to another place to reach another host. From the process of forming the previous conidia to the growth of the current conidia is called an infection cycle. The infection cycle does not only occur once, but many times so that the pathogen spreads and grows until it covers an increasingly large planting area. The repeated cycle of infection is called an endless chain of infection: dispersioninfection-colonizationsporulation-dispersion and so on. So an epidemic develops systematically, cycle by cycle, a polycyclic process. The chain of infection can be divided into two, namely: chain of infection“homogenus"that is, if the infection cycles are identical to each other, for example only consisting of conidia as a dispersion element as in downy mildew caused byPeronosclerospora maydisuntil now it is known that the dispersion unit is only conidia.The chain of infection can also be “heterogeneous",that is, if in the infection cycle various forms of spores play a role in contact with one another. For example, scurvy, Venturia inaequalisin apple plants in sub-tropical areas.Ascospores released from apple leaves that have fallen on the ground infect young leaves after winter. Then during the plant's growth in spring and summer, infection occurs repeatedly by conidiospores. In the leaves that fall in autumn, perithesia grow and develop to produce ascospores again and so on. So in one year the infection chain consists of one sexual infection with ascospores after winter and several asexual infections with conidiospores in spring and summer.