Phytophthora palmivora
Widmer, T.L., 2014. Phytophthora palmivora. Forest Phytophthoras 4(1). doi:10.5399/osu/fp.4.1.3557

Phytophthora palmivora


Phytophthora palmivora (E. J. Butler) E. J. Butler (1919) is a cosmopolitan pathogen with a wide host range, including some very important economic crops such as cacao, papaya, black pepper, rubber, coconut, and citrus. The center of origin is believed to be southeastern Asia (McHaw and Coffey, 1994). In 1907, Butler originally described a new species, Pythium palmivorum, from palms and coconut. In 1918 it was reclassified as Phytophthora palmivora (R einking, 1923). P. palmivora was placed in morphological group II by Stamps et al. (1990) and in clade 4 (Balci et al., 2008; Cooke et al., 2000) on the basis of ITS sequences of genomic rDNA. 

Etymology: From Palmyra palm (Borassus flabellifer), one of the tree species from which the pathogen was originally isolated.


P. palmivora is heterothallic with amphigynous antheridia and spherical oogonia. The caducous sporangia are papillate, varying in shape from ovoid-ellipsoid (Erwin and Ribeiro, 1996) to obpyriform (Q-Bank). Chlamydospores are terminal and intercalary averaging 33 µm in diameter.

Figure 1 Figure 2
Terminal chlamydospore of P. palmivora (left), P. palmivora oogonia with antheridia (right)
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Figure 3 Figure 4
P. palmivora caducous papillate sporangia (left) showing sympodial branching (right)
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P. palmivora is placed in the phylogenetic clade 4 together with P. megakarya and P. quercetorum. Sequencing data (Cooke et al., 2000; Kron et al., 2004) confirm the proposition of Oudemans and Coffey (1991), McHau and Coffey (1994), and Martin and Tooley (2003) that P. palmivora and P. arecae are conspecific.

Figure 5 Figure 6
Phylogenetic tree from


Colony morphology on V8 is a stellate pattern with aerial mycelium; hyphae are coralloid. Growth on CMA is sparse with no aerial mycelium. Growth occurs over the temperature range of 11° to 35° C; optimal temperature for growth is 27.5° to 30° C.

Figure 7 Figure 8
Growth of P. palmivora on potato dextrose agar (left) and V8 agar (right)

Distinguishing characteristics for identification

P. palmivora differs from P. megakarya morphologically in that it has narrow, medium length sporangial pedicels and spherical, narrow-stalk oogonia compared to the broad, short, and occluded sporangial pedicels and the pyriform, downward tapering oogonia of P. megakarya (Erwin and Ribeiro, 1996). P. quercetorum, also in clade 4, is homothallic in culture (Balci et al., 2008) while P. palmivora is heterothallic.

The searchable web-based database Phytophthora-ID is useful for rapid identification of Phytophthora species based on sequencing of the ITS or Cox spacer regions, followed by BLAST searching the database. Phytophthora-ID maintains a database of sequences that is selective for sequence accessions that come from trusted sources including published, peer-reviewed studies whenever possible.

Disease history

The primary forest disease caused by P. palmivora is black pod disease of cacao. The first published reports on cacao were in 1909 by Von Faber and by Maublanc, who described the causal pathogen as a new species, Phytophthora faberi (Ashby, 1929). In 1924, Butler reported that P. faberi and P. palmivora were the same species, so the earlier name, P. palmivora, took precedence. The primary impact of this disease is on the cacao pods (fruits), eventually infecting the beans within the pods rendering them of no commercial value. The disease is known throughout the world wherever cacao is grown. In Central and West Africa, P. palmivora is known to exist in the same areas with P. megakarya, and both species can cause black pod disease. P. palmivora is also known to have serious effects on other hosts such as citrus (canker, fruit rot, and root rot), coconut (bud rot and fruit rot), papaya (stem rot and root rot), black pepper (root rot and collar rot), and durian (canker, root rot, leaf blight, and fruit rot). Inoculum is spread through rain splash, wind, insects, and human activity.

Symptom of black pod disease of cacao (T. cacao) caused by P. palmivora.

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Impacts in the forest

Although P. palmivora has a wide host range of over a thousand plant species, including ornamental plants as well as horticultural and agricultural crops, the only major concern in a forest setting appears to be on cacao. P. palmivora is believed to be responsible for annual losses of 20-30% of the world's cacao crop (Erwin and Ribeiro, 1996). The isolation of P. palmivora from noncultivated forest soil in Ghana indicates that this species is indigenous to forest soils (Kakwa, 1974). Most other economically important hosts such as citrus, coconut, papaya, black pepper, and rubber are in closely managed agricultural settings, sometimes in close proximity to natural forests. In 1993, Bernard and Mitchell reported P. palmivora on red maple (Acer rubrum) for the first time in the U.S. However, no reports on the actual impact of this species on hardwood trees have been found to date.

Forest and wildland hosts and symptoms

On cacao, P. palmivora primarily causes a pod rot (black pod) but is also known to cause stem cankers and seedling blight. Black pod can be caused by either P. palmivora or P. megakarya. In Asia, Central America, and South America, the disease is caused by P. palmivora. In Central and West Africa, both species occur and either may cause black pod. Symptoms caused by P. megakarya and P. palmivora can be distinguished in the field because P. megakarya produces lesions with irregular edges on the fruit whereas lesions caused by P. palmivora have regular borders and are generally smaller (Erwin and Ribeiro, 1996). Pods are susceptible at all stages of development and may be infected at any place on the surface. The first symptom is a brown to black spot on the pod, which spreads rapidly in all directions and eventually covers the whole pod. The beans become infected internally about 15 days after the initial infection and are soon of no commercial value. Several other forest species are known to become infected and to maintain the pathogen at low levels but the impact on black pod disease itself is not fully understood.

P. palmivora also causes bud rot and fruit rot of coconut in wildland and agricultural settings. On other hosts, P. palmivora causes a range of symptoms such as root rot, cankers, and leaf blight. Economically important agricultural crops include durian, citrus, rubber, mango, black pepper, and papaya.

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Educational materials


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