Prevention is the best cure for banana viruses |
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| Increasd yield of small-scale banana production through improved crop management practices to control the spread and reduce the effect of banana virus diseases | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Smallholder growers in the Philippines and Uganda can now recognise virus infections in their banana plants. Simply spotting viruses early and pulling out the infected plants, then making sure new plants are healthy, helps double yields. The banana bunchy top and banana streak viruses devastate banana crops across South Asia and the Pacific. Now they are spreading in southern Africa. No varieties resistant to either virus have been found and, because chemicals don't work against viruses, prevention is the best option. Growers in Davao-Mindanao, in the Philippines, and in Rakai, Masaka and Ntungamo, Uganda, found that just by removing infected plants they reduce damage and prevent spread of the viruses. They also now make sure that they plant healthy plantlets, produced by low-cost tissue culture. Project Ref: CPP75:
Research Programmes: Crop Protection Programme Relevant Research Projects: Main Projects
Earlier/linked Projects:
Institutional Partners - Main Projects Lead Institute:
Partners & Collaborators:
Banana bunchy top caused by Banana bunchy top virus (BBTV) is the most devastating virus disease of banana and is present across all of south Asia and the Pacific and is currently spreading in Southern Africa. It is spread by the banana aphid (Pentalonia nigronervosa) and through infected planting material. Banana streak virus (BSV) is probably present in all banana-growing regions of the World, but is generally slower than BBTV to cause severe damage with initial symptoms often being confused for other problems. BSV is transmitted by several mealybug species and through infected planting material. No good resistance has been identified in Musa germplasm to either virus, and chemical treatments are not an option for viruses, so disease management has to be based on avoidance by preventing disease spread and removing sources of infection. The projects identified sustainable methods of managing both the diseases in small-holder banana plantations and the outputs comprise:
These outputs have converged with those of other projects to conclude that under small-holder banana production systems, it is necessary to adopt an integrated approach to crop management addressing all pests and diseases, and soil fertility. For this, the growers have to be able to identify the signs of the constraint and be aware of the threshold levels where it becomes necessary to remove diseased plants and replant with healthy plantlets. They also need the incentives to adopt this approach, including an affordable source of virus-tested "clean" planting material of the varieties they desire.
Main commodity: Bananas and Plantains, including East African Highland bananas There are lessons learnt about how resource-poor farmers perceive virus diseases and the general principles of how to detect/diagnose and control them, taking account of these perceptions and some generic constraints to adoption of such systems, that could be applied to other perennial or vegetatively propagated crops. Developing systems for increasing the supply and use of "clean" planting materials either for replanting where diseased plants have been rogued out or for planting new fields is potentially applicable to all the vegetatively propagated food crops (e.g. yams, cassava, sweet potato, cocoyam, Solanum potato) and tree crops (e.g. citrus, cocoa).
All the CPP projects on banana, particularly those focussed on East Africa, were operating as an effective cluster since early in the RNRRS. This allowed the sharing of resources and lessons learnt, and engendered a more holistic approach to the care of the crop to be adopted; necessary to improve banana productivity and sustainability. The importance of the clustering has been:
(NB: DFID/ODA have spent over £5M on banana research alone over the last 16 years - see Table 4) How the outputs were validated: The main outputs of the projects described are the research findings about the two virus diseases and approaches to controlling them, gained through laboratory and field experiments. The understanding of smallholder perceptions of banana diseases and the factors affecting uptake/adoption of alternative control practices were obtained through semi-structured surveys/interviews with small-hold growers in the Davao/Mindanao area of the Philippines and in Rakai, Masaka and Ntungamo in Uganda. Research on BBTV was carried out through collaboration between research partners from the Bureau of Plant Industries (Davao, Mindanao, Philippines), and the Natural Resources Institute (UK), with some support from the INIBAP-AP office and the Queensland Department of Primary Industries, Australia (for diagnostic tools). The BBTV projects did not have the resources and did not continue for long enough to have the specific outputs validated by end users or other intermediary organizations. Research on BSV was carried out through collaboration between research partners at the Ugandan National Banana Research Programme and NRI, with additional input from John Innes Centre (UK) and IITA (Nigeria and Uganda). Where the Outputs were Validated: Knowledge on the dynamics of the spread of BBTV was validated through three experiments in small-scale banana producers' plantations in Davao over 2.5 years. The recommended practice of early identification and roguing of BBTV-infected plants was validated by studying the incidence of BBTV in a portion of a small commercial plantation where the practice was standard. The results obtained were considered sufficiently rigorous to be published in a peer-reviewed journal [Smith MC, Holt J, Kenyon L, Foot C (1998) Quantitative epidemiology of Banana Bunchy Top Virus Disease and its control. Plant Pathology 47, 177-187.]. The perceptions and understanding of small-scale banana growers in Mindanao of diseases of banana, focussing on BBTV, and the recommended control practices were assessed through a semi-structured survey and focus group discussions with over 100 growers in the Davao area of Mindanao (in 1997). Replicated on-station field trials in Kawanda and Mbarara over 3 cropping cycles (mother and two ratoons) demonstrated that using improved crop management could increase the useable yield obtained from BSV-infected plants by up to 2x. Replicated screenhouse experiments and field trials in Rakai and Ntungamo confirmed that there is active spread of BSV and this is probably by mealybugs. Observation of 30 small-scale growers' fields in Ntungamo in 2001-2002 revealed that where growers adopted more of the recommended crop management practices, severity of BSV was generally less, resulting in greater yields. Surveys involving individual growers and focus-group discussions in Ntungamo, Masaka and Rakai in 2001-2002 revealed that most farmers were unaware of the cause of BSV disease symptoms and so did not understand the rationale behind the crop management practices being recommended to control the spread and impact of the disease. The research was of sufficient quality to warrant the award of two PhDs [Kubiriba J (2005) Epidemiology of Banana Streak Virus (BSV) in East African Highland Bananas (AAA-EA). PhD thesis, University of Greenwich, pp217. and Murekezi C (2006) Effects of banana steak virus and crop management on growth and yield of east African highland bananas (Musa spp., AAA-EA). University of Reading]. Who are the Users? The projects/outputs described in this proforma were relatively up-stream research and so any promotion of the outputs took place after the end of the projects and there is no direct evidence from the projects of the specific outputs being used. Outputs related to BBTV are being promoted and used in the INIBAP-AP coordinated project: "Collaborative banana research, development and extension for improved cropping systems". This is promoting the tissue-culture production of virus-tested banana by public-private partnerships for sale at relatively low cost to small-holder banana growers in Luzon (Philippines) so they can counter the recent BBTV epidemic and revitalize their production of the locally preferred variety "Lakatan". (details in table of annex). The outputs specific to BSV appear only to be being used by/promoted by the Uganda National Banana Research Programme through the development of training materials and conducting training (e.g. in the Benchmark sites programme). There is also an unconfirmed suggestion that KARI-Kenya is attempting to get BSV diagnostic tools working for testing mother plants prior to tissue culture. The less disease-specific approach of improving the supply of "clean" tissue-cultured banana plantlets (of both local varieties and some of the improved hybrids - e.g. some of the FHIA varieties) to small-holder banana growers to enable them to establish new "healthy" plantations is being promoted and used by several partnerships:
Where the outputs have been used: BBTV-specific outputs - INIBAP programme in Luzon, Philippines. BSV-specific outputs - Uganda (and possibly in Kenya?) some farmer training at benchmark sites, but appears not to be being widely promoted or used on the ground. BSV, unlike BXW is a slow, insidious problem whose impact on yield is not necessarily immediately dramatic, as it depends on the interaction of many crop management variables. Policy-makers, scientists (NARO) and technical advisors (including NAADS) are currently focused on the more visible and faster-acting BXW. More general banana Integrated Crop Management projects:
Scale of current use: BBTV - INIBAP Luzon. Approximately 400,000 plantlets (sufficient to replant about 20,000ha) of the locally preferred variety "Lakatan" were sold by Lapanday (A commercial banana grower-exporter in the Philippines) in 2005 alone. Also, 77 500 tissue-cultured planting materials of the different introduced and local cultivars were distributed to farmers (groups) in Luzon in 2005 and over 150 farmers/groups were trained in crop management practices to manage BBTV. BSV - No information on scale of current use of BSV-specific outputs. C3P - Currently focussed on BXW, but interventions to make available clean banana planting material are relevant to BBTV and BSV control (as well as to nematode and fungal diseases). Aims that 300 farmers per targeted district in Uganda and 300 farmers in each of other 5 countries receive and plant 40 clean suckers (produced on local macro-propagation units). Policy and Institutional Structures, and Key Components for Success: The organisations listed above in questions 12-14 have been instrumental in successfully promoting the outputs. Table 2 in the annex also lists these organizations/networks as well as several other that have had or potentially could have a role in promoting aspects of banana Integrated crop management (ICM). The main programmes and platforms that have assisted these broad outputs are:
Direct and Indirect Environmental Benefits: Immediate short-term - need to destroy infected plants and to control the spread of the vectors. Plants can be destroyed by application of herbicides but this is probably too expensive for most of the target farmers who should chop down and dig out the infected plants and all associated suckers and chop in small pieces to prevent re-growth. The critical step after plant elimination is replanting with planting material free of the viruses. If plants are eliminated before the diseases have spread widely, then plant cover is only momentarily disrupted on a small scale. However, if the disease has infested large numbers of plants, eradication and replanting with bananas/plantains or another crop may increase soil erosion. Long-term - if the control strategies are successful, a perennial banana and plantain cropping system with a diverse mix of varieties to satisfy local markets and consumption patterns will be re-established or conserved. I.e. a return to, or protection of, a cropping system which conserves soil, requires little soil disturbance and uses minimal pesticide. If the diseases are not controlled and move into new areas then Musa will become less productive and farmers will be forced to switch to other crops. In many cases, these are annual crops or root crops with frequent replanting. More soil tillage is required for the frequent replanting of cassava, maize, rice or other such crops. This can be expected to lead to increased erosion and run off. In addition, the biodiversity of Musa will be and is threatened; both SE Asia and Central Africa are centres of Musa genetic diversity For these reasons halting the spread of the diseases is in the long term environmental interests of the banana growing countries. Adverse Environmental Impacts: Short-term - destruction of infected plants if done on a large scale could result in increased soil erosion. There is the potential for adverse environmental impact from use of herbicide to kill infected mats and insecticide to prevent spread of vectors from infected mats when they are being destroyed, but since most target farmers are unable to afford or cannot access these pesticides the risk is minimal. Coping with the Effects of Climate Change, or Risk from Natural Disasters: Bananas are not seasonal so can be harvested at all times of the year. They are also a relatively resilient crop able to withstand short periods of drought or flood. Interventions that help increase the survival and productivity of the crop, and help maintain the Musa genetic diversity result in bananas being able to continue to produce in adverse conditions of climate change and other natural disasters. Relevant Research Projects,
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