Invasive Plant Pests Threatening Ethiopian Agriculture

Abstract

The human population and its food demands are increasing at an annual rate of 1.4%. Although world population will probably stabilize by the year 2050, this will require an increase of about 25% (Abesha and Gustavo, 2004) in plant productivity. These demands can be partially met by diminishing the impact of invasive pest and pathogens which represent 12% (James et <://., 1990) of the productivity. It is well recognized that threats by invasive pathogens such as Xanthomonas and phythoplasmas to horticultural commodities are increasing as a result of loose quarantine system, globalization, increased human mobility, climate change, and pathogen and vector evolution. These factors have combined to increase the spread of invasive plant pathogens (Anderson et a/., 2004). Taken in total with damage caused by emerging, re-emerging (e.g., new races, pathotypes, forms resistant to pesticides or antibiotics), and chronic/endemic pathogens, the potential for economic loss is significant in plant systems (Strange and Scott, 2005). Governments are responsible to protect agricultural and natural plant systems in their countries from invasive pathogens, while at the same time putting in place measures to prevent their own endemic pathogens from becoming invasive species in others. Although the private sector has a responsibility to produce clean plant products, safeguarding of agricultural and natural plant systems from introduced pathogens is usually considered a public good, and therefore a role of the government (Sheldrake and Turner, 2003). Plant disease diagnostic networks have developed worldwide to address the problems o f efficient and effective disease diagnosis and pathogen detection, engendering cooperation of institutions and experts within countries and across national borders. Networking maximizes impact in the face of shrinking government investments in agriculture and diminishing human resource capacity in diagnostics and applied pathology (Smith et a/., 2008). New technologies promise to improve the speed and accuracy of disease diagnostics and pathogen detection. Subsequently, it appears that, early and accurate diagnoses and pathogen surveillance on local, regional, and global scales are necessary to predict outbreaks and allow time for development and application of mitigation strategies. Citrus is an extremely important crop on a worldwide basis, and is grown wherever the climate is suitable. Total worldwide production of citrus is estimated at over 73 million metric tones (Wayne, 2001). Citrus is widely grown in Ethiopia and most cultivation in the south and southwest region is based on a small number of local varieties and in most parts o f the country it is grown by small scale producers with plantings of, often, less than 50 trees and on large scale plantations as well (Eshetu, 2006). Small scale commercial farms belonging to Federal Prison, Horticulture Development Enterprise, Agriculture Development Enterprises and others also produce citrus, for export to regional markets and local Agro-industries. Most of the citrus in commercial farms is produced by the Upper Awash Agro Industry Enterprise (UAAIE) which includes Merti Jeju, Nura Era, Tibila, and Awara Melka (Seifu, 2003). Citrus is also grown in Metehara, Melka Werer , Error Gota Gibe, Jima, Mizan Teferi, Bebeka, Tepi, Metu, Shewa Robit and Tisabalima (Seifu, 2003; Eshetu, 2006). However, the predominant citrus is produced by small scalc producers in the various regions of the country. Citrus canker and Huanglongbing (MLB) or citrus greening are two very serious diseases that occur in different parts of the world. Both diseases are labeled as threats because of their impact on yield (quantity or quality) and international trade, ability of the pathogens to survive and to spread rapidly, difficulty in controlling with available technology, and very high cost of disease management practices, This paper discusses different aspects of citrus canker (Xanthomonas cixonopodis pv. citri) and citrus Huanglongbing (greening) disease {Candidatus liberibacter) that are currently becoming invasive and devastating. Unfortunately, the two diseases are becoming threats to citrus production in various parts of Ethiopia in general, and in the Rift Valley, in particular. Advises on basic principles of management of these diseases is also suggested.