Module 3: Phytophthora ramorum
Module 2: Disease Management
Welcome Module 1: Biology, symptoms, and Diagnosis Conclusion Take the Exam Further Information

What is Phytophthora?

Disease Cycle

Seasonal Activity

Species Profiles

Virtual Dying Plant


Practice Questions 



Life Cycle

Phytophthora species are well adapted to the diverse environments that they encounter in different seasons. They produce several types of structures. Some ensure survival in the absence of a host plant.  Others are well suited for infecting plants or dispersing to other plants. All the structures are so small that a microscope is necessary to see them

Chlamydospores, a type of survival structure, in a Rhododendron leaf.

Photo by E. Oh.

Phytophthora produces two kinds of spores designed for long-term survival: chlamydospores (clam-EE-doe-spores) and oospores (OH-oh-spores).

The larger, round, thick-walled structure is the oospore, another type of survival structure. The smaller structure at the base is evidence of sexual reproduction.

Photo by P. Reeser.

Both types of spores are round and have thick walls that protect them.

The important difference is that chlamydospores are asexual (clonal) spores, whereas oospores result from sexual recombination.

Sexual recombination can be very important in increasing the genetic variability within a species. For example, it could lead to faster development of resistance to fungicides. 

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