Phytophthora nicotianae or black shank is an oomycete belonging to the order Peronosporales and family Peronosporaceae.

[4] Hosts include tobacco, onion, tomato, ornamentals, cotton, pepper, and citrus plants.

Root rot symptoms are observed on tobacco, poinsettia, tomato, pineapple, watermelon, and as well as African violet.

In tobacco black shank affects the roots and basal stem area, but all parts of the plant can become infected.

Chlamydospores are produced asexually and serve as long lived resting structures, surviving from four to six years.

Another asexual structure and secondary inoculum, appearing ovoid, pear, or spherical in shape are called sporangium.

These spores are produced and can either germinate directly or release motile zoospores within 24 hours of inoculation with the right conditions.

Splashing water from rain or irrigation can infect healthy plant leaves leading to more repeating secondary cycles.

Once the root surface is contacted, zoospores encyst and a germ tube will emerge penetrating the epidermis.

The hyphae are heterothallic and require two mating types to produce oospores, the sexual survival structure.

Saturated soil optimizes disease spread because water is used for dissemination of motile zoospores and sporangia.

Splashing water from rain or irrigation can infect healthy plant leaves leading to more repeating secondary cycles.

[10] Phytophthora nicotianae has a wide host range, affecting agriculture rich areas all over the world.

[8] Disease was observed near Georgia in 1915 and reached major tobacco growing areas of Kentucky and North Carolina in the 1930s and 1940s.

In North Carolina black shank can be found in every county that grows flue-cured tobacco and currently causes statewide losses of 1 to 2.5 percent per year.

Zoospores interact with the host by sensing and moving toward the nutrient gradients near the root tip and wounds of the plant.

Upon death of the host, the decomposing infected tissues will release the pathogen back into the soil, in the form of chlamydospores and zoospores.

[6] The action of P. nicotianae is amplified by the presence of root-knot nematodes, which through their own feeding habits, assist the pathogen in finding an entrance to the host.