Manuscript accepted on : June 11, 2008
Published online on: 08-02-2016
E. D. Fagbohun*, C. R. Falegan And J. A. Arowolo
Department of Microbiology, University of Ado Ekiti, P.m.b. 5363, Ado-Ekiti Nigeria.
ABSTRACT: Incidence and pathogenic variation among Phytopthora species was studied in some selected cocoa plantations in Ekiti State of Nigeria. Infected cocoa pods were collected from five selected plantations each at Ilu-Omoba, Aisegba, Ikere, Ijero, Ise/Emure and Aramoko and brought to the laboratory. Identification of fungal isolates were based on colony morphology, slide culture and pathogenicity tests. Isolates from Ilu-Omoba, Aisegba, Ikere-Ekiti and Ise/Emure produced white cotton-wool like colonies on potato dextrose agar, with spherical sporangia and narrow pedicel. Two isolates were obtained from Ise/Emure. These show characteristics similar to those obtained from Ilu-Omoba, Aisegba, Ikere-Ekiti axis and Aramoko axis. Isolates from Aramoko-Ekiti and Ijero produced sparse aerial mycelium with stellate appearance, and broad sporangia pedicel. All the isolate however produced chlamydospores. Healthy cocoa pods inoculated with isolates showed the characteristic Phytophthora pod rot symptoms of water soaked lesions, which gradually increases in size and turned black. Pathogenic variations were observed with the two groups of isolates. Isolates from Ilu-Omoba, Aisegba, Ikere-Ekiti and Ise/Emure were more virulent than those from Aramoko and Ijero. The colony morphology, cultural characteristic and pathogenicity tests observed show that the two groups of isolates belong to Phytophthora megakarya and P. palmivora. P. megakarya was more prevalent in Ilu-Omoba, Aisegba, Ikere, and Ise/Emure while P. palmivora was limited to Aramoko and Ijero-Ekiti. The same fungus P. megakarya was also more virulent than P.palmivora.
KEYWORDS: Incidence; Pathogenic variations; Phytophthora species; Cocoa plantations
Download this article as:![icon_pdf](https://biotech-asia.org/wp-content/uploads/2016/05/icon_pdf.png)
Copy the following to cite this article: Fagbohun E. D, Falegan C. R, Arowolo J. A, Phytophthora black pod disease in Ekiti state of Nigeria: Species differentation and pathogenic variation. Biosci Biotechnol Res Asia 2008;5(1) |
Copy the following to cite this URL: Fagbohun E. D, Falegan C. R, Arowolo J. A, Phytophthora black pod disease in Ekiti state of Nigeria: Species differentation and pathogenic variation. Biosci Biotechnol Res Asia 2008;5(1). Available from: https://www.biotech-asia.org/?p=6549 |
Introduction
Black pod disease is one of the major diseases limiting the yield of cocoa in Nigeria. Different species of Phytophthora are known to cause this disease (Brasier and Griffin, 1979). Two species, Phytophthora palmivora and P. megakarya have been attributed to the black pod disease in Nigeria (Opeke and Gorenz, 1974). Though P. palmivora is reported worldwide as a causative agent of black pod disease of cocoa, however, P. megakarya is the major pathogen reported from Nigeria, Equatorial Guinea and Ghana (Brasier and Griffin, 1979).
Various reports have been published on the estimates of worldwide losses resulting from black pod disease (Padwick, 1956; Mederios, 1977; Ward et. al. 1981; de Figueiredo and Lellis, 1982). In Nigeria, the estimate ranges from 30-60%. of total cocoa produced (Ward et. al., 1981). Though P. megakarya is more virulent than P. palmivora, however infection varies according to both location and climate (Luterboacher, 1993). Since the two species are present in Nigeria, species differentiation as well as climate and geographical location could play a considerable role in the epidemiology of black pod disease from different parts of the country.
Ekiti State is a medium cocoa growing area in Nigeria, however there are few reports in literature concerning the epidemiology of black pod disease of cocoa in the state. Arowolo and Fagbohun (2001) reported the occurrence and distribution of Phytophthora canker on cocoa trees as well as surveying the occurrence of Phytophthora spp in the soil of some cocoa plantations in Ekiti State.
Therefore, the present study reported here was carried out to identify the type of Phytophthora species associated with black pod/ pod rot disease of coca and their pathogenicity in cocoa plantations in Ekiti State.
Materials and Methods.
Naturally infected cocoa pods were obtained from five plantations each at Ilu-Omoba, Aramoko, Ikere, Aisegba, Ise/Emure and Ijero-Ekiti.They were kept in separate sterile polythene bags and brought to the laboratory.
Isolation of Pathogen
The infected pods were sterilized using 70% ethanol. The lesion from each infected pod was cut out using sterilized knife. Pieces of the samples from each plantation were inoculated into plates of potato dextrose agar(PDA). The plates were incubated at 280C for five days. Pure cultures were obtained by sub-culturing the isolates on pre sterilized PDA medium and stored at 40C.
Identification of isolates
Slide culture
One square centimeter of PDA was cut from a plate and placed on a sterile glass slide using sterile needles. Each slide received different isolates. The slides were placed on glass rods in Petri dishes containing 20% glycerol in water until adequate growth occurred. (Zoberi 1967).
The sporing surface of the pure culture of each isolate was teased out into a drop of alcohol and the preparation was observed under the microscope for fruiting bodies and mycelia branching. To study the colony morphology of each isolate, the method of Brasier and Griffin (1979) was used. After five days in total darkness, the isolate were observed against a dark background.
Pathogenicity Test: Mature healthy green cocoa pods of different sizes and ages were harvested from each farm and labelled. Five cocoa pods were inoculated with seven-day old culture of each isolate and placed in moisture sterilized polythene bags. They were incubated at 280C for seven days. Observations were carried out daily on the inoculated pods for one week and infection rating was given a rating of between (+) and (+5).(+) being no infection and +5,a completely rotten pod)(Firman and Vernon, 1970)
Results and Discussion
Isolates from Ilu-Omoba, Aisegba, and Ise/Emure on PDA produced a white cotton-wool like aerial mycelium over the entire medium. The sporangia were spherical to fairly ovate, round base with narrow pedicel. Brasier and Griffin (1979) described isolates of Phytophthora spp with similar colony morphology and of sporangia types as the ones identified above as P.megakarya.
Isolates from Ikere produced colonies similar to that of Ilu-Omoba, Aisegba and Ise/Emure however, they produced sporangia with broader pedicel. This could be regarded as a variant of the Ilu-Omoba, Aisegba and Ise/Emure isolates. The isolates from Aramoko produced whitish colonies with stellate appearance and sharply defined edges. Aerial mycelium was sparse. The sporangia has longer pedicel. These characteristic were the features described for isolates of P. palmivora by Turner and Wharton (1960), and Brasier and Griffin (1979). Table 2 is a summary of pathogenicity tests carried out with the isolates. There were variation in the rate of infection from Ilu-Omoba, Ikere and Ise/Emure on inoculated cocoa pods produced lesions with a more diffuse leading edge and considerable more fungal growth on the surface which extend with a few millimeters of the lesion edge. These characteristics when compared with Brasier’s isolates confirmed the fungus to be of P. megakarya. P.palmivora does not usually produce the white fungal bloon at the earlier stage of infection as P. megakarya isolates (Okaisabor 1965 and Brasier et. al., 1981). From the observation reported on pod infection, it is obvious that the isolates from Ilu-Omoba, Aisegba and Ikere are more virulent than Aramoko isolates. It has been reported that P.megakarya is more virulent in infected pods than P.palmivora(Maddison and Griffin 1981).This further confirmed the identification of Ilu-Omoba, Aisegba and Ikere isolates as P.megakarya and the Aramoko and Ise/Emure as P.palmivvora.
In Nigeria, P.palmivora is the predominant species, while P.palmivora occured to a certain extent. In this study, both species are present in Ekiti-State, though P.palmivora is not as widely distributed as P.megakarya. Further more Ilu-Omoba, Aisegba, Ikere and Ise/Emure axis represents the zone where major cocoa production is carried out in the state and where P.megakarya is the predominant type. Though considerable difference in epidemiology of black pod disease is known to exist within Phytophthora species (Madisson and Griffin, 1981), however, infection varies according to climate and location. It is expected that the zone where P.megakarya predominates will be more heavily affected than those of P.palmivora. Though no concrete evidence has been presented on the epidemiology of black pod disease in state,but areas of highest annual rainfall are known to suffer the greatest losses from the black pod disease (Butler, 1981;Wood, 1974)
In the classification of Opeke and Gorenz (1974), the state falls under the category of medium loss area. In a study yet to be published, the two species sometime appear together in the same location in Ekiti.The variation observed in the rate of pathogenicity of the two groups of isolates in the state could play a major factor in the epidemiology of black pod disease in Ekiti State. Hence, there is need to carry out an epidemiological survey of the areas to determine the level and severity of the disease to facilitate the development of appropriate control measures.
Table 1: Distribution and Identification of Isolates From Five Towns In Ekiti State.
Towns | 1 | 2 | 3 | 4 | 5 |
Aramoko | a | a | a | a | A |
Ijero | a | a | a | a | A |
Aisegba | b | b | b | b | B |
Ikere | b | b | b | b | B |
Ilu-Omoba | b | b | b | b | B |
Ise/Emure | ab | ab | ab | ab | Ab |
Key
a =Phytophthora palmivora
b=P. megakarya
Table 2: Result of pathogenicity test of various isolates from selected Farms/Towns In Ekiti State.
Towns | 1 | 2 | 3 | 4 | 5 |
Aramoko | +3a | +2a | +3a | +3a | +3a |
Ijero | +3a | +3a | +3a | +3a | +3a |
Aisegba | +5b | +3b | +5b | +4b | +4b |
Ikere | +5b | +4b | +5b | +5b | +5b |
Ilu-Omoba | + 5b | +4b | +4b | +5b | +4b |
Ise/Emure | + 4ab | + 4ab | + 4ab | + 4ab | + 4ab |
Key
Disease Rating
+ | No infection |
+ + | Slight infection |
+ + + | Moderate infection |
+ + + + | Severe infection |
+ + + + + | Very severe infection |
Isolates
a= Phytophthora palmivora b= P. megakarya
References
- Arowolo, J.A. and E.D. Fagbohun:Occurrence and distribution of Phytophthora canker on cocoa in Ekiti State, Nigeria. African Journal of Science 1(1): 100-106. (2001)
- Brasier,C.M and M.J. Griffin: Taxonomy of Phytophthora palmivora on cocoa. Trans.Brit.Myco.Soc. (1): 111-143. (1979)
- Brasier,C.M., Griffin, M.J and A.C Maddison: The cocoa black pod Phytophthoras in Epidemiology of Phytophthora on cocoa in Nigeria(eds P.H. Gregory and A.C Maddison). Phytopathological paper no 25, Commonwealth Mycological Institute, (1981) Kew;England pp 18-31.
- Butler, D.: Microclimatic factors associated with the incidence of black pod disease of cocoa. Proc 6th inter. Cocoa Res. Conf. Caracas, Venezuela 1977.pp171-180. (1981)
- de Figueiredo. J.M. and W.J.Lellis: Alternativa na applicaceo de fungicides a blaxo volume no controle da podridao paradados frutos docacaueiro. Informe Tecnico – 1981 CEPEC: Itabuna, Brazil,pp 47. (1982)
- Fagbohun, E.D. and J.A. Arowolo: Phytophthora species in the soils of some cocoa plantations in Ekiti State of Nigeria Appl. Trop. Agric. 6(2): 116-121. (2001)
- Firman, I.O and A.J.Vernon: Cocoa canker caused by Phytophthora palmivora. Ann. App. Biol. 65:65-73. (1970)
- Luterbacher, M.C: Current status and distribution of Phytophthora megakarya in Ghana: 11th International cocoa Research Conference.pp 29- 32. (1993)
- Maddison, A.C. and M. J. Griffin: Detection and movement of inoculum in Epidemiology of Phytophthora on cocoa in Nigeria (Eds P. H. Gregory and A. C. Maddison) Phytopathological paper no 25, Commonwealth Mycological Institute, Kew;England pp 31-50. (1981)
- Medeiros, A. G. :Sporulation of Phytophthora palmivora (Bult.) In Relation to epidemiology and control of cocoa black pod disease. Publicao Especial CELPA, Itabuna, Brazil. (1977):
- Okaisabor, E.K. Preliminary studies on the epidemiology of Phytophthora palmivora.1 Outbreak of black pod disease of cocoa. Nigeria Agric. J.2:67-70. (1965)
- Opeke, L.K. and A. M. Gorenz.:Phytophthora pod rot, symptoms and economic importance, In P. M. Gregory(ed) Phytophthora Diseases of cocoa, Longman. London pp 117-124(1974)
- Padwick, G.W.:Losses caused by plant disease in the tropics. Phytopathological paper No 1 Commonwealth Myco. Inst. Kew, England. (1956)
- Turner,P.O. and A.L. Wharton : Leaf and stem infections of Theobromae cacao L. in West Africa caused by Phytophthora palmivora (Bult.).Trop. Agric. (Trinidad) 37: 321-324. (1960)
- Ward, M. R; Maddison,A.C. and A. A. Adebayo: The epidemic on sprayed cocoa at Gambari. In P.H. Gregory and A.C. Maddison (eds) ‘ Epidermiology of Phytophthora on cocoa in Nigeria’. Phytopathological paper No 25, Commonwealth Myco. Inst. Kew, England. (1981)
- Wood, G. A. R.: Black pod meteriological factors: In Phytophthora Diseases of cocoa edited by P. H. Gregory, Longman Press Ltd. London pp.153-159. (1974)
- Zoberi, M. H.: A simple technique for preparing and preserving slide cuture. Trans Brit Myco. Soc. 50:1-57-158. (1967).
This work is licensed under a Creative Commons Attribution 4.0 International License.