Plant Pathology Concepts and Principles

General Comments on Disease Cycles for Plant Health Management

The approach, treatment, and/or concept of "DISEASE CYCLE" as considered in this presentation differs from some of the classical approaches. We consider the disease cycle to be the cycle of the disease and accordingly treat the cycle not as the life cycle of the causal agent with a host appended; but rather the totality of the disease from infection by the causal agent through disease expression and over wintering and returning to infection.

This does not minimize, in any way, the importance of knowing the life cycle of the causal agent. Understanding the biology of the causal agent is critical to establishing Plant Health Management Stategy. Equally important is understanding the biology of the host, its cultural conditions and unique characteristics.

It is a daunting task for one to attempt to "memorize" the disease cycle for every disease which is interesting, or (in the case of a course) required) Therefore, one must formalize ones approach and focus on some general aspects universal to all diseases which will aid in Plant Health Management. Remember that a Disease Cycle is not synonymous with the life cycle of either the host or the parasite but rather, like the concept of pathodeme, is the result of both host and parasite life cycles functioning simultaneously.

Plant Health
- As a starting point; consider plant cultural factors that impact plant disease. In this area one would consider the potential for Resistant Varieties, Crop Rotation strategies, Planting Timing, Alternate Cropping, etc. In this area one would also consider site; its location, preparation, and maintainance.
Infection
- At the juncture between "Plant Health" and "Infection" is the point where infection occurs; leading to parasitism followed, potentially, by pathogenesis. This is the "beginning" of the disease. Under "Infection" one considers; what is the inoculum, how is it spread (vectored), is there anything unique about the inoculum propagule (i.e. zoospore, single stranded RNA, motile, etc), are there multiple forms of inoculum?
- Under "Infection" one considers the biology of the parasite and what enables it to become parasitic and then pathogenic.
Disease Symptoms
- Under Disease Symptoms one describes the appearance of the disease. One also considers those factors that lead to epidemics once the disease becomes established. A consideration of pre- and post- infectional "control" strategies are appropriate here.
Over Season
- How does the parasite maintain itself, and in what form, from season to season. Is the "over seasoning" inoculum ephimeral or durable (must is reinfect another plant to maintain is viability or can it remain viable.for extended periods)? Is vector control in the off season a viable control strategy? What is the role of sanitation?

This is not intended to be an all inclusive list. It is presented so that you may be able to formalize your approach to understanding disease cycles. There are many other factors not mentioned above. Some are unique to a given disease; while others may be universal.

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

jpartridge1@unl.edu