Fungi isolated from diseased indigenous plants in Namibia.
Abstract
During the past few years, disease symptoms in many Acacia trees in the Windhoek Municipality area and the rest of Namibia have been observed. This observation triggered the investigation of phytopathological aspects that are reported in this chapter. The importance of indigenous trees of the Namibia flora is apparent considering that Namibia has two old deserts within its borders: the Namib Desert and the Kalahari Desert. Nambia’s tourism and meat industry are dependent on the indigenous trees of Nambia flora. The trees are the primary source of vegetation land cover (attracting tourists), and they provide browsing food matter to domestic livestock and wild animals (sources of meat). Hence, it is important to ensure that a healthy vegetation is maintained in this area.. This survey is the first dedicated step to find ways of protecting them from disease-causing agents. The aim of this survey is to investigate the possible causes of disease symptoms in trees. It is important to understand the biology of the pathogenic agents to propose a possible method to control the diseases. The survey involved sampling leaves, stems and roots from dying trees that show symptoms such as branch girdling, gum oozing and defoliation, suspicious general twig wilting and die-back. The survey was carried out in places where symptoms were observed. The tree surveys were done on Aloe zebrina, Tylosema esculentum, Syzygium and Acacia species. Primary isolations from plant material and then single-spore pure cultures were made for identification. In this chapter, we report isolation and identification of Microsphearopsis sp., Dreschelra sp., Botryosphearia spp., Acremonium spp., Coniothyrium sp., Phellinus spp., Cytospora sp., Fusarium sp., Scytalidium sp., Phoma spp., Gliomastix sp., Trichoderma koningii, Peacilomyces variotii, Alternaria citri and Curvularia palescens from the diseased trees. This work is still ongoing. This study paves way for proper designing of control methods to protect crops, trees and their biodiversity. The protection of plant biodiversity ensures better reaping of food products and other ecosystem services and products. Without knowledge of the identity of these disease-causing agents, it is not possible to accurately identify and manage threats to food production and threats to the native botanical biodiversity of Namibia.
Keywords
- Acacia mellifera
- Acacia karroo
- Syzygium
- fungal pathogens
- Namibia tree diseases
1. Introduction
Fungal plant pathogens, if not controlled one way or the other, can have devastating effects on biodiversity, forest structure and dynamics, commercial plantations, agro forestry and urban environments. This is especially the case with introduced (exotic) pathogens. A well-known example is that of
Die-back on A
Yet another close example is that of the baobab disease threat. Baobab trees are very resilient and can survive an extraordinary amount of abuse by humans, animals and natural conditions. Very little, however, is known about the diseases that affect these trees. In recent years there have been numerous reports on baobab tree mortality
The death of several large baobabs [5] in the Nyae Nyae conservancy in Namibia: Both sooty mould and the exudation symptoms were observed on the trees. It, therefore, appears that the cause of death may be a combination of diseases or an unidentified pathogen.
The increasing number of reports of diseased and dying trees in Namibia [9-13] emphasizes the need for urgent investigation of the causes of these deaths. It is necessary to determine whether these reports are isolated incidences or if there is an epidemic underway that can threaten the survival of indigenous trees. Furthermore, it is important to understand the fungal assemblages of these trees to understand possible future disease outbreaks. One of the greatest challenges to tree health management is the fact that so little is known regarding the fungal biodiversity on trees and the role these fungi play in tree health. In this chapter, the symptoms observed on dying trees and potential causal agents of death are reported. In plant health biology and forestry conservation, the firstdedicated step is to determine causes of plant diseases, which is a primary objective of this investigation. Yearly, calls have been received from farmers about plants dying or manifesting life-threatening symptoms [9-14] (see Figure 1). Some of these reports have been partially investigated and yet others remain to be investigated.
2. Materials and methods
2.1. Description of study site and population
The study was carried out in Oshikoto and Otjozondjupa regions of Namibia, where the disease reports on trees have been received from. In addition, the survey was carried out on forest stands where some of the species occur in Erongo, East and West Kavango and Zambezi regions.
The study was exploratory in nature and used standard mycological methods to investigate the identity of fungi causing diseases on plant species based on previous report calls received and reports existing in the media. In cases where no reports have been made, field surveys were carried out to observe symptoms in native forest stands.
During the survey, diseased samples from leaves and small branches and twigs were collected (see Figure2). These were then brought to the laboratory at the University of Namibia for isolation of fungal organisms. The pure cultures of these microbial organisms were then stored in a type culture collection facility and used for further classical microbiological analyses and genetic analyses to determine the identity of the organisms. Fungi were identified based on morphology and ITS DNA sequencing data. Further, the pure cultures were used to test Koch’s postulates by inoculating the possible pathogens into healthy seedlings.
For the
Survey trips were conducted in various sites in Namibia, including Windhoek, Dordabis, Grootfontein, Katima Mulilo, Omaruru, Swakopmund, Rundu, Popa Falls and Rehoboth between 2003 and 2013 to collect leaves, stems and roots of
3. Results and discussion
The main objective is to investigate the decline and death of forest tree species in Namibia with a hope to develop management strategies to reduce the impact of the disease and help ensure the continued survival of an important component of the Namibian plant ecosystem for continued supply of ecosystem services. For this survey, for a number of specific fungal pathogens in key Namibian ecosystems. For this, the surveys conducted served as the groundwork for future research field of microbiology, plant pathology and plant protection. The results of this research helped to answer some key questions regarding fungal plant pathogens that occur in Namibia. Results (see Table 1) will expand our knowledge pertaining to the distribution, impact and origin of these pathogens. This knowledge is also essential to understand the working of these native ecosystems at a basic level, which is potentially important for the conservation of these ecosystems.
It is anticipated that the findings reported here will articulate into the Namibia’s National Forest Programme aimed at promoting the sustainable use of the country’s forests. In this national aim it is important to ensure forests that are healthy. If forest tree species are declining because of diseases, then sustainability becomes impossible. These data reported here assist in creating linkages with various sectors, such as the National Forestry Research Division in Okahandja in Namibia to promote forestry research, protect and conserve forest areas against destructive diseases and pests.
Most of the fungal species recorded in Table 1 have also been recorded elsewhere in the literature [9-15] as fungal pathogens affecting similar plant species that we investigated in this study or affecting other plant or crop species, which points to the fact that it is important to keep surveillance of plant disease as these fungal pathogens can easily be transported worldwide and be able to cause diseases or death in similar or other plant species.
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Several fungal species have been isolated and some of them for the first time in diseased
4. Conclusions and recommendations
Several fungal species associated with diseases in
The results reported in this chapter can be used to develop a catalogue of fungi associated with crop and tree diseases in Namibia forest and possible control methods. In addition, the results can be used to devise long-term strategy for breeding for disease-tolerant forest species, especially those that have immediate commercial value, e.g.,
Acknowledgments
This work was supported financially by the University of Namibia. Jean Damascene Uzabakiriho, Martin PL, Prof I Mapaure, Prof Jolanda Roux and Dr Mutsa Takundwa and the University of Namibia are greatly acknowledged for the field work.
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