Published Date: 2007-08-31 14:00:08
Subject: PRO/PL> Black pod, cocoa - Puerto Rico: 1st report
Archive Number: 20070831.2865
BLACK POD, COCOA - PUERTO RICO: FIRST REPORT
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: August 2007
Source: The American Phytopathological Society, Plant Disease 2007;
91(8): 1051 [edited]
[Reference: B. M. Irish et al: First report of _Phytophthora
palmivora_, causal agent of black pod, on cacao in Puerto Rico. Plant
Dis 2007; 91(8): 1051; DOI: 10.1094/PDIS-91-8-1051B]
First report of _Phytophthora palmivora_, causal agent of black pod,
on cacao in Puerto Rico
Black pod or _Phytophthora_ pod rot is the most economically
important and widespread disease of cacao, _Theobroma cacao_ L. Total
losses due to _Phytophthora_ exceed USD 400 million worldwide (1),
and several species are known to attack cacao with _P. palmivora_
(E.J. Butler) E. J. Butler as the most common. All plant parts are
infected, but pod infections are particularly damaging.
Symptoms resembling those of black pod disease were observed at the
National Plant Germplasm Collection System of cacao at the USDA-ARS
(US Department of Agriculture-Agricultural Research Service) Tropical
Agriculture Research Station (TARS) in Mayaguez, Puerto Rico for a
number of years. During May 2005, to determine the etiology of the
disease, small, surface disinfested sections of pod lesions were
placed on water agar and incubated for 4 days. The formation of
papillate, deciduous, ellipsoidal to ovoid sporangia produced on
sympodial sporangiophores on fruits, fit the description of _P.
palmivora_ and the identification was confirmed on cultures (2).
Chlamydospores were readily observed in diseased pods and observed in
pure cultures (2). Hyphal tips were used to initiate stock cultures.
For pathogenicity tests, healthy mature pods were surface disinfested
and placed in a humidity chamber lined with moist paper towels. A
total of 8 isolates were tested on 4 fruits per isolate and the
pathogenicity test was repeated once. Inoculum was prepared and
adjusted to 104 sporangia per milliliter. Pods were inoculated and
evaluated daily for 2 weeks.
For molecular analysis, the internal transcribed spacer (ITS) region
of the ribosomal RNA gene cluster was amplified, purified, and
sequenced for all 8 isolates. The ITS sequences for 2 isolates were
identical and exhibited strong similarity (more than 99 percent
identity) to that of 3 previously described isolates of _P.
palmivora_ from cacao.
_P. palmivora_ has been reported on citrus, coconut, black pepper,
and _Arracacia xanthorrhiza_ in Puerto Rico (2,3) and inoculum may
have originated from these hosts or imported on cacao planted into
the cacao collection before 2000. USDA-ARS-TARS is the official site
for the cacao germplasm collection; thus, a detailed integrated pest
management plan has been implemented, that includes evaluation for
resistance, sanitation measures, and use of fungicides to reduce
disease levels. Decreasing incidence and severity of this disease is
a top priority.
To our knowledge, this is the 1st report of _P. palmivora_ on cacao
in Puerto Rico.
1. MCT Braga et al. Agrotropica 1:108, 1989.
2. D Erwin and OK. Ribeiro: Phytophthora Diseases Worldwide. The
American Phytopathological Society. St. Paul, MN, 1996.
3. E Rosa-Marquez. J. Agric. Univ. P. R. 84:53, 2000.
[_P. palmivora_ is found worldwide on cocoa and can cause losses as
high as 95 percent in very humid climates. An average of 20-30
percent of the worlds' cocoa crop is lost to this pathogen each year.
In some areas, cocoa cannot be grown economically because of black
pod. Pods can be infected at any age. The most serious economic loss
arises from infection during the 2 months prior to ripening, which
can totally destroy the pods. Symptoms start with a small translucent
spot on the pod, which progressively turns darker brown and expands
rapidly. Eventually the pod shrivels up, turning into a black, hard
mummy. Cankers and dieback may result from infections of stems and branches.
The fungus is spread by insects, mechanical means, plant debris,
water, and wind. Multiple infections from several sources may occur
in plantations with epidemics developing from a series of foci. Thus,
disease management is difficult since trees too tall to be
effectively sprayed or harvested can continue to disperse inoculum.
Cultural techniques such as shade reduction, regular harvesting, and
frequent weed control may reduce infection, and fungicides are an
option. Resistant cultivars are available for some areas. Biological
control measures are being investigated.
There are 3 other _Phytophthora_ species that have also been found
associated with black pod on cocoa, however, these are less common
(for more information see ProMED mail 20070713.2243).
_P. palmivora_ is a very common pathogen in tropical environments
with more than 150 host species affected. Some of the most important
hosts are black pepper (_Piper nigrum_), rubber (_Hevea
brasiliensis_), durian (_Durio zibethinus_), coconut (_Cocos
nucifera_), cocoa (_Theobroma cacao_), breadfruit (_Artocarpus
altilis_), and papaya (_Carica papaya_). The pathogen causes bud rot
on coconut (one of the worst diseases of this crop) and other palms,
as well as root and fruit rots on a variety of hosts.
_Arracacia xanthorrhiza_ (family _Umbelliferae_; common names
arakacha, Peruvian parsnip, white carrot) is a root crop from the
Andean region used by the ancient Incas.
Locator map of Puerto Rico:
Detail map of Puerto Rico:
Pictures of black pod symptoms:
Summary by the authors:
Background information on black pod disease:
Information on black pod and other cocoa diseases and control:
Information on black pod and other _P. palmivora_ diseases and hosts:
_P. palmivora_ on palms:
_P. palmivora_ taxonomy:
Information on _A. xanthorrhiza_: