Phytophthora infestans

This student page has not been curated.

Classification

Domain: Eukaryota; Phylum: Heterokontophyta; Class: Oomycota; Order: Peronosporales; Family: Pythiaceae; Genus: Phytopthora

Species

Phytophthora infestans

NCBI: [1]

Description and Significance

Phytophtora infestans is an oomycete protist. P. infestans was originally thought to be a fungal species due to its filamentous structure and metabolic strategies, but recent biochemical and phylogenetic analyses has revealed that P. infestans is only remotely related to fungi and is more closely related to heterokont algae (Kumar and Rzhetsky 1996, Van de Peer and De Watcher 1997). P. infestans growth structure is fungal-like, with the mycelium usually coenocytic and consisting of hyphae 5 to 8 µm in diameter (Erwin and Ribeiro 1996). P. insfestans cell walls are primarily composed of cellulose and β-glucans and lack chitin (Bartnicki-Garcia 1968). P. infestans is the causal agent of late blight in potatoes, lead to the Great Irish Famine in the mid nineteenth century, and causes approximately US $3 billion dollars worth damage annually world-wide (Duncan 1999). P. infestans is distributed worldwide, including major potato growing regions in Europe, North America, and South America (Goodwin et al. 1994).

Genome Structure

In 2009 the Phytophthora infestans genome was sequenced (1). The genome size is estimated to be 237 Mb consisting of a high G-C content, about 52% (2,3). Microscopic analysis showed that there are 8-10 chromosomes (3). It is a diploid organism, meaning there are two sets of the chromosomes present within each cell (4).

Cell Structure, Metabolism and Life Cycle

Life Cycle
Phytophthora have two kinds of resting or survival spores that they produce, both of which have thick cell walls that allow them to survive in suboptimal environments for long time periods. The two kinds of spores are oospores, formed from sexual recombination and chlamydospores, asexual survival spores(4).

Some species of Phytophthora are homothallic and some are heterothallic. Homothallic species can reproduce with just one thallus being present. Heterothallic species can reproduce only if two different thalli interact from mating types A1 and A2 (5). Phytophthora infestans is heterothallic(6). Under cool wet conditions, Phytophthora oospores or chlamydospores which will germinate to form hyphae or directly produce sporangia. The sporangia are able to detach and travel in the air(6). The sporangia then release free swimming zoospores that have two flagella, one tinsel and one flagellate. The flagella allow the zoospore to travel in water on the surface of leaves as well as in the soil (6). Once a zoospore reaches the plants root or leaf surface it forms a cyst. The encysted zoospore then germinates and forms hyphae on the host surface. The tube like hyphae invades the plant leaf or root and allows the cell to get food (4). After the Phytophthora infects the plant, it can produce sporangia and zoospores to further infect other tissues of the same plant or nearby plants. The Phytophthora will then produce more survival structures, oospores or chlamydospores, to overwinter and provide a source of inoculum for the following year’s life cycle(7).
Metabolism
Once the plant host has been infected the hyphae are used to take up nutrients. Nutrients required for growth are organic carbon source, oxygen, phosphorus, nitrogen, hydrogen, sulfur, calcium, magnesium, and iron(8).
Cell Structure:
The cell wall is composed mostly of (1-3) β-D-glucans, (1-6) β-D-glucans, and cellulous(9).

Author

Page authored by Jayme Olsen and Pete Nelson, students of Prof. Jay Lennon at Michigan State University.

<-- Do not remove this line-->