Texas Invasive Species InstitutePhytophthora capsici
Blight of Peppers
Class: Oomycetes
Order: Peronosporales
Family: Pythiaceae
Photographer: Gerald Holmes, Valent USA Cooperation
Source: Bugwoord.org
Description
In Greek, Phytophthora capsici means “plant destroyer of capsicums”. This pathogen is an oomycete (aka: water-mold), a fungus-like eukaryotic microorganism, which attacks seeds and seedlings of an extensive range of plants. It is from the same genus as Late Blight (Phytophthora infestans) and Sudden Oak Death (Phytophthora ramorum). Symptoms vary on host plant but overall they include seed/fruit rot and seedling blight. The blight in seedlings causes the roots to discolor and the seedlings uproot. Infection usually starts at the soil line and spreads lesions up the plants stems (pictured center). Stem lesions become dark and result in girdling and plant death. The seed and fruit rot appears as a whitish gray fungal-like growth that mummifies and decays the fruit (pictured far right). Leaf discoloration and foliar blight is common also. If left unmanaged it can decimate whole crop fields, especially because it can remain viable in the soil after crops have been rotated with non-host plant crops.
Host Plant: Found in a wide range of hosts mainly from 3 plant families. Solanaceae: Chili and Bell peppers, Tomatoes and Eggplants; Cucurbitaceae: Cucumber, Cantaloupes, Squash, Melons and Pumpkins; Fabaceae (legumes): Lima beans, Soy beans and snap peas. Along with spinach, Swiss chard and turnips.
Ecological Threat: It can infect more than 50 plant species, including several weed species which allow it to spread quickly and across several types of crops. It is an aggressive disease, capable of causing complete crop failures. It has been increasing in severity in the United States in recent years.
Biology: Phytophthora capsici is a soil-borne pathogen which overwinters as oospores (thick-walled resting spores) in the soil or in plant debris. Oospores are resistant to desiccation and cold temperatures, and can survive in the soil for many years. Phytophthora capsici can infect seedlings, vines, leaves and fruits of a plant, which means it can infect a host plant at any stage of growth. This oomycete is heterothallic meaning it produces both a male (antheridium) and female (oogonium) type of gametangia; but it can reproduce asexually as well. Reproduction results in an oospore that may germinate into a germ tube or give rise to sporangia which then germinate and give rise to zoospores. The zoospores are motile (pictured left) which allow for the pathogen to produced more than one infection cycle per crop cycle (polycyclic).
History: First described on a crop of chili peppers in Las Cruces, New Mexico in 1922. By 1937 it was found on honey dew and tomatoes along with other cucurbits, in California and Colorado. It was found sporadically in Florida in 1993 and by 1997 it had become and still is a chronic problem for pepper and summer squash crops. It reached Texas wheat crops in 2004 and has become a long-standing problem of peppers grown in the Lower Rio Grande Valley. In 2006 in Texas it also spread to pumpkin and winter squash crops.
U.S. Habitat: Low areas of fields where water accumulates. It grows best at 80oF and spreads in warm and wet conditions. The sporangia are spread by irrigation water, rain and drainage water.
Distribution
Native Origin: Unknown, potentially tropical regions.
U.S. Present: All states except Alaska.
Management
Phytophthora capsici is also very adaptable and can quickly become resistant to a fungicide; for example, populations in New York are resistant to mefenoxam (Ridomil). This is why integrated management programs are necessary even for minimal control. Thus far, no cucurbit cultivar with reasonable resistance is available. There are some pepper species that are tolerant of this blight. Initially it was thought that crop rotation would help significantly. However, over time crop rotation is virtually ineffective because the pathogen can survive for several years in the soil. If no oospores are present in the soil then crop rotation can be effective; but P.capsici has been present in the fields then oospores are probably present also. Research is clearly needed to develop effective strategies for the management of Phytophthora blight caused by P. capsici on cucurbits and other vegetables. Since this pathogen can start in areas with high water levels, good crop drainage is necessary to prevent this oomycete from spreading. Select well-drained fields, and avoid planting into low-lying areas. Raised beds are recommended for non-vining cucurbits. Also, it is suggested to not actively work in wet fields because all clothing and equipment that acmes into contact with the oospores can further spread them.
Text References
Hausbeck, M. 2004. Phytophthora lessons learned: Irrigation water and snap beans. The Vegetable Growers News 38:2829.
Kreutzer, W. A., Bodine, E. W., and Durrell, L. W. 1940. Cucurbit diseases and rot of tomato fruit caused by Phytophthora capsici. Phytopathology 30:972-976.
Satour, M. M., Butler, E. E. 1967. A root and crown rot of tomato caused by Phytophthora capsici and P. parasitica. Phytopathology 57: 510-515.
Internet Sources
http://www.apsnet.org/edcenter/advanced/topics/EpidemiologyTemporal/Pages/Disease%20Progress.aspx
http://phytophthora.pppmb.cals.cornell.edu/photos13.html
http://www.veginfo.msu.edu/bulletins/phytophthora.htm
http://www.extento.hawaii.edu/kbase/crop/Type/p_capsi.htm
http://edis.ifas.ufl.edu/vh045
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