HOME PAGE   List of Fact Sheets   Glossary

Figure 1. Morphology of spore types of Phytophthora capsici. Upper row, Variation in shapes of papillate, caducous sporangia with long pedicels. Lower row, Globose oogonia with amphigynous antheridia (oospores are plerotic); torulose mycelium. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

Figure 2. Morphology of Phytophthora capsici (sensu Tsao 1991) formerly known as the atypical Phytophthora palmivora MF4 (sensu Griffin 1977). Upper row, Umbellate formation of sporangiophores; formation of sporangia in a sympodium. Lower row, Oogonium with an amphigynous antheridium containing a globose oospore; ellipsoid, caducous sporangia with long pedicels. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

Figure 3. Life cycle of Phytophthora capsici. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999) Click image to see larger view.

Figure 4. Culture of Phytophthora capsici grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

Figure 5. Colonies of Phytophthora capsici grown on V-8 juice agar. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 6. Sporangium of Phytophthora capsici (×1,000). (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 7. Oogonium of Phytophthora capsici with an amphigynous antheridum and a plerotic oospore. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 8. Cucurbit fruit infected by Phytophthora capsici. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 9. Blight caused by Phytophthora capsici on the stem of a bell pepper plant. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 10. Lesions caused by Phytophthora capsici on bell pepper leaves. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 11. Symptom caused by Phytophthora capsici on bell pepper fruit. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 12. Root and crown rot of bell pepper, caused by Phytophthora capsici. (Courtesy Jean B. Ristaino; Reproduced from Ristaino and Johnston, 1999)

Figure 13. Fruit rot of pumpkin, caused by Phytophthora capsici. (Courtesy M. T. McGrath; Reproduced from APS Digital Image Collections, Diseases of Vegetables, American Phytopathological Society, St. Paul, MN)

Introduction

Phytophthora capsici  Leonian (1922)

 

Phytophthora capsici was first reported by Leonian on chili pepper (Capsicum frutescens) in New Mexico in 1922 (Leonian, 1922). The pathogen has a wide host range and causes disease on peppers, tomatoes, eggplants, and cucurbits. Various taxonomists, including Mchau and Coffey (1995), Tsao (1991), and Tsao and Alizadeh (1988), have broadened the species concept of P. capsici to include a range of morphological characters and the two isozyme groups CapA or Cap 1, including P. palmivora MF4, and CapB or Cap 2, including most tropical crop isolates. Aragaki and Uchida (2001) argued for a narrower species concept, referring several tropical isolates from cacao, black pepper, and macadamia to the new species P. tropicalis. The taxonomy of P. tropicalis as a species needs further delineation and is described in a separate fact sheet. P. capsici is a member of Waterhouse's group II species (Stamps et al., 1990) (Figs. 1–3). 

Cultural Characteristics

Cultures are radiate and fluffy (Figs. 4 and 5). The minimum temperature for growth is 10°C, the optimum temperature for growth is 28°C, and the maximum temperature for growth is higher than 35°C.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are narrow, widening slightly at the base of the sporangium and branching irregularly. Simple sympodium forms in water or may be umbellate in tropical isolates.

 

Sporangia:

Sporangia are caducous and often irregular, nearly spherical, broadly ovoid, and obturbinate or elongated (Fig. 6). Sporangia are papillate and large. Most tropical isolates (CapB) produce ellipsoid-lanceolate sporangia. They are 17.4–38.7 × 32.8–65.8 µm (Fig. 6). They are often distorted and have more than one apex and are papillate. The pedicel is long and is 10 µm or more in length and up to 100 µm in some isolates.

 

Chlamydospores:

Chlamydospores are rare or absent in most CapA isolates from pepper but abundant in tropical isolates from black pepper and cacao (CapB isolates). When present they are 28–29 µm in diameter with a wall thickness of 2.4–2.7 µm.

 

Hyphae:

Hyphae are fairly coarse and 5–7 µm wide. Hyphal swellings are occasionally produced by some isolates in aqueous cultures.

 

Sexual Structures

 

P. capsici is heterothallic. There are two mating types in P. capsici, A1 and A2. Each mating type produces hormones that are responsible for gametangia differentiation in the opposite mating type.

 

Antheridia:

Antheridia are amphigynous and 15 × 17 µm.

 

Oogonia:

Oogonia appear frequently in single cultures of some isolates, but in others, they are only on pairing A1 and A2 mating types. The wall of the oogonia is yellowish brown. Oogonia are spherical and can vary in size from 23 to 50 µm. Oospores are plerotic.

 

Oospores:

Oospores nearly fill the oogonium and are thin walled (2–6 µm) (Fig. 7). The mean oospore diameter of pepper isolates is 23.7–34.9 µm (Ristaino, 1990). Size of the oospore varies with different hosts.

Host Range and Distribution

P. capsici infects 51 genera in 28 plant families. P. capsici causes a devastating disease on bell pepper (Capsicum annuum) and cucurbit (Cucumis sativus) crops in the United States and worldwide (Fig. 8). The pathogen can also cause disease on eggplant (Solanum melongena), tomato (Lycopersicon esculentum), and other members of the family Cucurbitaceae. For a more extensive list of hosts, see Erwin and Ribeiro (1996). Host specificity was considered a taxonomic criterion by Tucker in 1933 (Tucker, 1933), but it is now known that the pathogen can infect many tropical species, including black pepper, cacao, and cotton bolls. P. capsici has been found in Europe (Bulgaria, France, Italy, Greece, Spain, and Russia), Asia (China, India, Iran, Israel, Japan, Korea, Lebanon, Malaysia, Saudi Arabia, and Turkey), North America (Canada, United States, and Mexico), Central and South America, and West Indies (Stamps, 1984).

 

Host	Common Name	Disease	Geographical Distribution
Capsicum annuum	Bell, sweet, red, or green pepper	Blight of leaves, fruits, and stems	Worldwide
Capsicum frutescens	Chili pepper	Blight of leaves, fruits, and stems	Worldwide
Cucurbitaceae family members	Cucumber, squash	Blight of fruits and stems	Worldwide
Gossypium spp.	Cotton	Blight of leaves, bolls, and stems	California
Lycopersicon esculentum	Tomato	Blight of leaves, fruits, and stems	Worldwide
Macadamia integrifolia	Macadamia nut	Blight of leaves, fruits, nut, and hull	Hawaii
Piper nigrum	Black pepper	Blight of leaves, fruits, and stems	Brazil, Guatemala
Theobroma cacao	Cocoa	Pod rot	Brazil, Mexico, Cameroon, Costa Rica
Sechium edule; Solanum melongena	Eggplant	Blight of leaves, fruits, and stems	Costa Rica
Spondia purpurea	Jocote, red mombin	Blight of leaves, fruits, and stems	Costa Rica

Symptoms

P. capsici causes stem and fruit rot of Capsicum spp. and soft rot of tomato and cucurbit fruits (Figs. 8–13). P. capsici causes a root and crown rot, as well as an aerial blight of leaves, fruit, and stems, on bell pepper (Capsicum annuum), tomato, cucumber, watermelon, squash, and pumpkin (Ristaino and Johnston, 1999). Oospores are believed to provide the initial source of inoculum in the field, and the disease is polycyclic within seasons. On the pepper fruit, the disease appears first as a small, dull green, water-soaked spot that quickly spreads, covering up to more than one-fourth of the fruit. The infected fruits can develop lesions that are typically covered with white sporangia. Tissue may become dry and sunken and turn a straw color after exposure to the disease. On the leaves, circular, grayish brown, water-soaked lesions are common.

 

Fruit Rot and Root Rot of Cucurbits:

Disease in tomatoes and cucurbits can manifest in one of two ways. Small, reddish brown lesions or discolorations can appear on the fruit. These areas grow and become dark green, eventually becoming brownish with irregular margins. Large, brown, water-soaked lesions can also appear with irregular margins, eventually creating well-defined margins on fruit.

 

Blight of Macadamia:

P. capsici can infect the flower and the nut of macadamia. P. capsici initially causes a dark brown to black discoloration on the nut. Sometimes it can penetrate under the husk of the nut and kill the kernel.

 

Buckeye Rot, Root Rot, and Crown Rot of Tomato:

Symptoms include irregularly shaped, water-soaked lesions on the fruit with a bull's-eye pattern. As the diseased area expands, the center becomes dark brown to black and newly infected areas turn light brown. Disease can also be detected by the rapid wilt and complete collapse of younger plants; cankers develop along the roots of older plants, followed by the wilting and necrosis of leaves.

 

Diagnostics:

Traditionally, P. capsici has been recovered by isolation of the pathogen from infected tissue and plating onto a semiselective medium. The pathogen can also be isolated from the soil following soil dilution plating in dilute water agar onto a semiselective medium such as Masago's medium. Also, a leaf disk baiting assay, in which circular disks of leaves are floated on saturated soil, provides a high level of pathogen detection. Leaf disks can also be plated onto semiselective media for detection. A polymerase chain reaction (PCR) assay has also been developed for detection of the pathogen (Ristaino and Johnston, 1999).

References

Aragaki, M., and Uchida, J. Y. 2001. Morphological distinctions between Phytophthora capsici and P. tropicalis sp. nov. Mycologia 93:137-145.

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

Leonian, L. H. 1922. Stem and fruit blight of peppers caused by Phytophthora capsici sp. nov. Phytopathology 12:401-408.

Mchau, G. R. A., and Coffey, M. D. 1995. Evidence for the existence of two distinct subpopulations of P. capsici and a redescription of the species. Mycol. Res. 99:89-102.

Ristaino, J. B. 1990. Intraspecific variation among isolates of Phytophthora capsici from pepper and cucurbit fields in North Carolina. Phytopathology 80:1253-1259.

Ristaino, J. B., and Johnston, S. B. 1999. Ecologically based approaches to management of Phytophthora blight on bell pepper. Plant Dis. 83:1080-1089.

Stamps, J. 1984. Phytophthora capsici. CMI Descr. Pathog. Fungi Bact. 836:1.

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew Surrey, England.

Tsao, P. H. 1991. The identities, nomenclature and taxonomy of Phytophthora isolates from black pepper. Pages 185-211 in: Diseases of Black Pepper. Proc. Int. Pepper Community Workshop on Black Pepper Diseases. Y. Sarma and T. Premkumpr, eds. National Research Centre for Spices, Calicut, Kerala, India.

Tsao, P. H., and Alizadeh, A. 1988. Recent advances in the taxonomy and nomenclature of the so-called "Phytophthora palmivora" MF-4 occurring on cocoa and other tropical crops. Pages 441-445 in: Proc. Int. Cocoa Res. Conf., 10th. Cocoa Producers' Alliance, Lagos, Nigeria.

Tucker, C. M. 1933. The distribution of the genus Phytophthora de Bary. Univ. Mo. Agric. Exp. Stn. Res. Bull. 184.