Sustainability of banana-based agroecosystems affected by Xanthomonas wilt disease of banana

Banana (plantains inclusive) in addition to being an important food and income security for over 70 million people across the African Great Lakes region (AGLR), is an important source of several regulatory and supporting services that to date have receive little attention. The recent outbreak of Xanthomonas wilt disease (XW) of banana (first reported in 2001) has compromised food and income security of the households and communities in the banana-based agroecosystems. XW effects on other ecosystem services are not well known and could affect the sustainability of these agroecosystems. XW management has been mainly reactive and mitigative and the disease has as such persisted and continues to spread. Understanding of the risk factors at landscape and field/ farm level are thus crucial. This study explored strategies for preventing and minimising shocks caused by XW disease outbreaks and improving the adaptive and/or buffering capacity of banana-based agroecosystems. To achieve this, the study i) determined retrospectively the XW-driven land-use changes and trajectories across landscapes in eastern DR Congo, ii) potential effects XW and land-use changes on the supply of key ecosystem services, and iii) developed XW risk maps for the AGLR and banana producing zones across Africa. At farm/ field level, iv) field level risk factors including the role of intercrops and weeds in harbouring and perpetuating XW, and v) the effect of banana leaf pruning to integrate intercrops on the efficiency of the system as a basis for discouraging and/or improving the intercrop management were determined. Finally, vi) the study explored the opportunity of integrating shade and drought tolerant species within heavily shaded banana fields so as to increase biomass production without profoundly affecting performance of the banana crop. To retrospectively characterise land-use changes/ trajectories due to XW and to determine XW effects on ecosystem services, focus group discussions, a four-cell analysis, diagnosis of farmer fields and a review of available literature were conducted. The dominance of the banana declined across all XW affected landscapes with increases in importance of other crops, mainly annuals. Crop diversity increased at household level but not at field level. XW was observed to also reduce the supply of supporting and regulatory ecosystem services. These findings suggest a need for an ecosystem services broad framework for addressing XW and other diseases of banana and other crops. At landscape level, XW incidence and a range of covariates were used to develop spatial spread maps of XW disease. XW increased with increasing precipitation and declining investment in disease and crop management. The spatial XW spread map highlights XW hotspots, front lines (e.g. eastern DR Congo) and the vulnerable landscapes with low (e.g. north-western Tanzania) or no XW (northern Mozambique). The eastern DR Congo, a zone where the plantains (Musa AAB) and the East African highland bananas (Musa AAA) meet was a major hotspot and is thus a potential gateway for XW to spread into the plantain belt of Central and West Africa. These maps are a good starting point for guiding proactive strategies for XW prevention, eradication and control. To elucidate the field/ farm level risk factors of XW a combination of laboratory and screenhouse experiments and a farm diagnostic study were used. Xanthomonas campestris pv. musacearum the causal organism of XW was observed to survive within some banana intercrops (e.g. maize, millet, sorghum, sugarcane) and weeds (Canna spp. and wild sorghum), with XW characteristic symptoms on millet, sorghum and Canna spp. Insect spread while collecting nectar, sap and pollen, plant to plant spread through the rhizome are important for XW perpetuation whereas the pathogen does not survive for long in absence of a living host. Thus the risk from the annual crops was rated zero to low, from sugarcane (perennial and propagates through the stem and rhizome) as low-moderate and from Canna spp. (propagates through the rhizome, highly susceptible and prevalent on farms) as moderate to high. Field diagnostic studies only showed a 0.02% disease incidence in Canna spp. XW risk on farm was instead lowered by growing banana cultivar mixtures and increasing access to information on disease epidemiology and management; and increased by the presence of the highly susceptible ABB banana types. Though Canna spp. has no association with the observed XW risk on farm it warrants close monitoring. The impact of cultivar mixtures on XW is novel and needs to be further investigated and integrated into the current XW management package. At field level, farmers prune banana leaves to increase light intercepted by the shorter crops. This practice currently enhances XW spread. Field experiments and a bio-economic optimisation model (FarmDESIGN) were used to explore the impact of these practices on the performance of the system. The model was also used to explore different external input (hedges, inorganic fertilizers and organic manure) scenarios for the system. Severe leaf pruning (to 4 leaves) was inefficient both agronomically and economically. Mild pruning (7 leaves) however improved the agronomic efficiency whereas unpruned banana (as intercrop or sole crop) was more efficient economically. Moderate leaf pruning to integrate legumes and not pruning at all could thus be considered as a trade-off between agronomic and economic efficiency for the banana-legume intercrop system. Trade-offs occurred between nitrogen input (minimized) and operating profit, soil organic matter balance and protein yield that were maximised. Profound improvements for all the above objectives only occurred with addition of external inputs, especially inorganic fertilizers and manure. For example, for the no or low input scenario(s), the model predominantly allocated land to severely pruned banana-legume intercrop and bush bean monocrop. In contrast, with addition of external inputs, the model allocated land to the more profitable options i.e. unpruned banana either as a sole crop or intercrop with legumes. Discouraging severe leaf pruning and improving the performance of the system for all objectives will necessitate investments in external inputs. These findings are a good basis for co-innovating the system for better performance. The FarmDESIGN model is thus useful for supporting field level explorations, decision making and overall co-designing of the banana agroecosystems. Available literature was also reviewed to identify potential shade and drought tolerant species for integration into heavily shaded banana fields. Integration of such species within the banana fields will increase overall biomass yield, minimise XW spread through leaf pruning and improve the overall performance of the system. This study thus shows XW to still be an important threat across landscapes in the AGLR and to both indirectly and directly affect the supply of a broad range of ecosystem services. Adopting proactive and holistic measures taking to account the broader range of ecosystems services is crucial at farm and landscape level for managing the disease. At field level, understanding the risk factors including crop management practices, and the role of other plant species in a system is important. This study also proposes agroecological practices (e.g. such as cover crops, hedges, crop cultivar mixtures) for improving the buffering and adaptive capacity of the banana-based agroecosystems.</p

An alternative to complete banana mat uprooting: assessing the effectiveness of continuous cutting at soil level of all shoots in a mat on speed for corm decay

The complete uprooting of diseased mats/fields (CMU) is one of the recommended control options for Xanthomonas wilt of banana. CMU is labour intensive, time consuming and disturbs the soil structure, exposing fields to erosion. CMU often involves exportation of whole plant biomass, affecting soil fertility. The potential of continuous cutting at soil level of all shoots in a mat until complete corm decay in situ as an alternative to CMU was assessed. The first experiment was established using 224 banana mats in their third cropping cycle. All the plants were cut down at soil level, meristems were removed, and sweet potato and bush bean planted. In a repeat experiment with 180 banana mats, a wide range of treatments were applied on top by cutting and removing the apical meristems. These included the: injection of 2,4-D herbicide into the centre of each corm; removal of a cone shaped section from the center of each corm; and creation of a 20 cm deep incision in the center of each corm; in combination with the application of soil or farmyard manure substrate on cut surface. In the first experiment, re-sprouting stopped at 8 months while corms fully decayed after 25 months. Annual intercrops did not influence re-sprouting and corm decay rate. Similar re-sprouting trends occured in the repeat experiment. However, 2,4-D application significantly (P<0.05) lowered decay time, with 12-47% of corms decomposed at 8 months compared with 0-20% in other treatments without 2,4-D. In the 2,4-D treatments, 100% of corms had decomposed compared with 36-80% in other treatments by the 20th month. Deep incisions or cuts did not significantly hasten decomposition. Soil or manure substrate addition had no advantage when compared with the cut surfaces without substrates. A cost-benefit analysis showed a five times higher net income with continuous cutting of re-sprouts when compared with CMU

Variation in nectar volume and sugar content in male flowers of Musa cultivars grown in Rwanda and their non-effect on the numbers of visiting key diurnal insect vectors of banana Xanthomonas wilt

Insects are a major mode of banana Xanthomonas wilt (XW) spread. High insect activity has been blamed for the high XW incidence in ‘Kayinja’ (ABB-genome) dominated banana landscapes across east and central Africa. ‘Kayinja’ male bud nectar composition reportedly contributes to high insect activity. The variation in nectar composition with agro-ecological zones and banana cultivars and its influence on the number of visiting insects in Rwanda were assessed. Three male buds were collected per cultivar for nectar extraction and analysis using a high performance liquid chromatography. Nectar volume and sugar concentrations varied (P<0.001) across 27 banana cultivars, annual seasons and agro-ecological zone. The highest nectar volume was recorded among the East African highland cooking cultivars (AAA-genome) in the high altitude site and the short-heavy rainy season. Nectar contained three sugars: glucose, fructose and sucrose, though hexose (glucose and fructose) was dominant. The three sugars varied significantly (P<0.001) within each cultivar. The total nectar-sugar concentration ranged from 2.3–32%, with the highest among dessert cultivars ‘Kamaramasenge’ (AAB-genome) and ‘Gisukari’ (AAA-genome). No strong correlation occurred between insect population and total nectar sugar concentration or nectar volume. Insect populations were rather influenced by the weather conditions, the long rainy season characterized by moderate well distributed rainfall recording the highest insect populations as compared to the short rainy season (with heavy rainfall) and the dry seasons

Management of Banana Xanthomonas Wilt: Evidence from impact of adoption of cultural control practices in Uganda

Banana Xanthomonas Wilt (BXW) is an important emerging and non-curable infectious plant pathogen in sub-Saharan Africa that can cause up to 100% yield loss, negatively impacting sustainable access to food and income to more than 100 million banana farmers. This study disentangles adopters into partial and full adopters to investigate the factors that are relevant to sustain the adoption process of BXW control practices and quantifies the impact of adopting the practices. Data from a randomly selected sample of 1200 banana farmers in Uganda where the disease is endemic was used. A multinomial logit model was used to determine the factors affecting adoption of control practices and augmented inverse probability weighting was employed to estimate the impacts of adoption on banana productivity and sales. Results show that training a woman farmer and having diverse sources of information about BXW control practices increased adoption of the control practices and reduced the disease incidences. Farmers who adopted all the recommended control practices achieved significantly the highest values of banana production and sales. We conclude that improving information access through farmers’ preferred communication channels, having women-inclusive trainings, and a combination of cultural practices are effective ways for sustaining adoption of the control practices

Symptomless banana suckers sourced from Xanthomonas wilt infected fields are a viable alternative for seed within infected banana-based landscapes lacking access to clean planting materials

Xanthomonas wilt (XW) caused by Xanthomonas campestris pv. musacearum (Xcm) is an important constraint to banana production in East and Central Africa. The use of clean planting materials (CPM) for establishing new fields/ re-planting rouged fields/mats is recommended. However, banana is mainly produced by resource-poor small-holder households with no/limited access to CPM. We assessed XW incidence in fields planted with symptomless suckers sourced from fields with >70% XW incidence and the role of Xcm-soil inoculum on XW persistence in North Kivu Province, eastern DR Congo. Symptomless suckers were planted in i) fields previously with banana having >70% XW incidence, 10 days after rouging and ii) fields previously under grass fallow. Symptomless suckers planted in fields previously under grass fallow served as checks. To contrast, healthy suckers and healthy macro-propagated plantlets were established in similar field typologies. Each treatment combination had three replicates of 30 plants. Additional experiments established in September, 2014 in South Kivu Province using symptomless suckers from fields with incidence levels varying from 1 to 90% assessed the reproducibility of the North Kivu results. In the North Kivu trials and when using symptomless suckers, relatively low cumulative XW plant incidences of 3.6 and 4.2% were recorded in fields previously under grass fallow and fields with >70% initial XW-incidence, respectively. The resulting fields were well established, suggesting that suckers sourced from diseased fields could potentially be used in zones with no access to CPM. Even lower incidences (0 to 0.28%) recorded in South Kivu further support this. Plant incidences of 1.8 and 2.9% were respectively observed in previously diseased fields planted with healthy macro-propagated plantlets and healthy suckers compared with zero incidence levels in the disease-free fields, confirming the role of residual Xcm-soil inoculum in infections

A community resource persons’ training guide: improving food and nutrition security through banana-based farming systems and foods

The information in this manual was selected following gaps identified at community level through focus group discussions and household surveys. The guide first describes what food security implies, it then goes on to give basic concepts on nutrition, i.e., types of nutrients, role in the body and local sources. The Guide goes ahead to describe how to make balanced family meals using locally available resources. The guide gives details on management of banana farms, post-harvest handling of the bananas and appropriate processing and cooking/combination methods that will enhance nutrient quality and promote better health. Last but not least, information on food safety and hygiene is also given