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Adapted from the keynote addresses made by David Jones and Richard Markham at the ISHS/ProMusa Symposium on ‘Recent Advances in Banana Crop Protection for Sustainable Production and Improved Livelihoods’.
June 2009
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When farmers started cultivating bananas, disease problems were probably not severe enough to encourage the selection of disease-resistant clones over susceptible ones. The early cultivation of banana would have occurred in clearings in the rainforest by shifting cultivators and later in gardens mixed with other crops by more settled agriculturists. Many cultivars with differing genetic backgrounds and differing reactions to pathogens and pests would most likely have been grown together. Disease and pest problems seem to have emerged only when banana began to be planted on a large scale as a monoculture of certain favoured cultivars.
The susceptibility of many banana cultivars to pathogens may have been inherited from Musa acuminata subspecies banksii and errans, which have contributed to almost all banana cultivars. These two subspecies are more susceptible to disease than other M. acuminata subspecies. At the other end of the spectrum, Fe’i banana cultivars, which are derived from different Musa species, seem less prone to disease problems, although they have never been grown in large plantations.
The first disease epidemics were caused by the fungus Fusarium oxysporum f. sp. cubense. Symptoms of Fusarium wilt were first described in Australia in 1876 on Silk bananas. First reports of the disease on Gros Michel in the Americas come from Costa Rica and Panama in 1890. It seems likely that the pathogen was distributed on planting material that was mass propagated for plantation use. The scene was set for an epidemic in banana plantations.
At the same time as the Fusarium wilt problem was at its height in the Americas, another serious fungal pathogen began to make its presence felt on the international scene. Sigatoka leaf spot, caused by the fungus Mycosphaerella musicola, was first recorded in Java in 1902. Sigatoka leaf spot did not kill plants, but affected yields because it caused leaf necrosis, which reduced photosynthetic capabilities. In addition, fruit on or from affected plants ripened prematurely, which was of concern to exporters. However, worse was yet to come.
Black leaf streak, caused by the leaf spot fungus Mycosphaerella fijiensis, was first identified in Fiji in 1963. It was quickly found to be more virulent than Sigatoka leaf spot on Cavendish cultivars and to attack cultivars that were hitherto resistant to leaf spot, such as those in the plantain subgroup. It was also more difficult to control, and more regular applications of fungicide were needed in plantations.
The export industry was saved, at least temporarily, by the use of Fusarium wilt-resistant Cavendish cultivars and fungicides effective against Mycosphaerella leaf spots. However, problems still continue to plague the many smallholders who grow susceptible dessert banana cultivars and cannot afford fungicides to control leaf spot diseases. Fortunately, many cooking banana cultivars favoured by people in developing countries are resistant.
Other fungal, bacterial and viral diseases are locally important, whereas the burrowing nematode is the most important root parasite of banana in lowland tropical areas. The most damaging insect pest of banana is the rhizome-attacking banana weevil.
A review of banana research and development efforts suggests that the major pre-occupations of banana researchers – leaf spots, Fusarium wilt, bacterial wilts, bunchy top, nematodes, weevils – have not greatly changed over the last 20 years and that we have not ‘solved’ any of the major problems of growers. In the meantime, new pathogen problems, such as Xanthomonas wilt, have cropped up, and others in which research effort has been invested, such as the streak virus complex, remain intractable.
Meanwhile, many of the solutions proposed, such as high-yielding, disease-resistant hybrids, genetically transformed versions of existing cultivars and forecasting systems to reduce spray applications, also look discouragingly familiar. And even where potential solutions have been delivered as promised by researchers, they have not been widely adopted by producers. On the other hand, papers presented at the ISHS/ProMusa Symposium do suggest a move away from such ‘single-technology’ solutions towards more integrated, knowledge-based approaches, which recognise the complexity of both the biophysical and the socio-economic dimensions of crop production problems.
This trend is evident across the whole spectrum of research, from genetic modification projects that start by trying to understand the finer details of plant-pathogen interactions, to organic banana projects that seek to understand the underlying processes of crop and agro-ecosystem health, indicating some convergence between what would previously have been considered ‘high-tech’ and ‘low-tech’ approaches.
It is also encouraging to see a greater emphasis on the social and policy environment that can enable or inhibit the adoption of new technologies, as well as the process of producer-level innovation as a whole. Unfortunately, the multidisciplinary study of complex systems is not cheap, and several years of consistent investment may be required to yield results. Similarly, the adoption of relatively complex, knowledge-based technologies implies a serious investment in capacity building at various levels. The onus is now on advocates of such approaches to demonstrate that the required investment is truly cost effective in terms of greater impacts and sustainability.
In conclusion, it is argued that better targeting of research efforts and concerted international action provide the key to ensuring that the substantial investments required by integrated, knowledge-based approaches are indeed cost effective in practice. ProMusa offers a framework for consensus-based priority setting and objective-oriented collaboration that can help to bring geographically dispersed efforts together and focus them on solving the latest wave of problems confronting banana producers, large and small.
Click here for information on how to get a copy of the proceedings of the symposium.
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