The response of Musa cultivar root systems to a tree shade gradient

Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011

Workshop 3: Pests and diseases in bananas - projecting the effects of climate change.

Over several decades, ProMusa has addressed important disease threats such as black leaf streak (black Sigatoka), Fusarium wilt, banana streak viruses and Banana bunchy top virus

Bananos y plátanos en sistemas de producción complejos: lecciones para la sostenibilidad.

Aproximadamente 50% del banano mundialmente se produce en sistemas mixtos en diferentes asocios con cultivos perennes y anuales. Mientras la producción para exportación y para ciertos mercados nacionales del banano en monocultivo se ha intensificado con el uso creciente de insumos externos, la intensificación de los sistemas complejos ha presentado retos para la ciencia

Dispersal limitation and fire feedbacks maintain mesic savannas in Madagascar

Madagascar is regarded by some as one of the most degraded landscapes on Earth, with estimates suggesting that 90% of forests have been lost to indigenous Tavy farming. However, the extent of this degradation has been challenged: paleoecological data, phylogeographic analysis, and species richness indicate that pyrogenic savannas in central Madagascar predate human arrival, even though rainfall is sufficient to allow forest expansion into central Madagascar. These observations raise a question—if savannas in Madagascar are not anthropogenic, how then are they maintained in regions where the climate can support forest? Observation reveals that the savanna–forest boundary coincides with a dispersal barrier—the escarpment of the Central Plateau. Using a stepping-stone model, we show that in a limited dispersal landscape, a stable savanna–forest boundary can form because of fire–vegetation feedbacks. This phenomenon, referred to as range pinning, could explain why eastern lowland forests have not expanded into the mesic savannas of the Central Highlands. This work challenges the view that highland savannas in Madagascar are derived by human-lit fires and, more importantly, suggests that partial dispersal barriers and strong nonlinear feedbacks can pin biogeographical boundaries over a wide range of environmental conditions, providing a temporary buffer against climate change

Preliminary evaluation of improved banana varieties in Mozambique

Banana (Musa spp.) production in Mozambique is largely confined to the Cavendish variety that is eaten as a dessert. On the other hand, banana is a staple food crop in many countries in sub-Saharan Africa. The introduction of a range of high yielding and disease resistant cooking and dessert varieties in Mozambique could play a potential role in ensuring food security and raising incomes of millions of small scale farmers. In the framework of a USAID-funded project on dissemination and evaluation of improved banana varieties, plantlets of new Musahybrids were distributed to small-scale farmers. In addition, several demonstration plots and an on-station trial at the Agrarian Research Institute of Mozambique (IIAM), Umbeluzi research farm were established. The objectives of this study were (i) to evaluate the general performance of the hybrids in the different locations andanalyse data collected from one of the sites, and (ii) to assess farmer acceptability of the hybrids in one of the agro-ecologies in Mozambique. The FHIA (Fundacion Hondurena de Investigacion Agricola) hybrids performed relatively well in the more moist agro-ecologies and where irrigation was available, but not in the drier areas in the south of Maputo. Although ‘FHIA 17’ was the most vigorous, this variety took the longest time to produce a bunch. The hybrid, ‘SH 3640’ produced the largest bunch but this was not significantly different from that of‘Grand Naine’ the local check used in the trials. The hybrid ‘SH3460’ and ‘Grand Naine’ emerged as the best cultivars in terms of post-harvest quality and acceptability. Less than 50% of the participants indicated their preference for ‘FHIA17’, ‘FHIA21’ or ‘FHIA23’. Feedback from farmers involved in the on-farm activitiesindicated that those from the central and southern parts of the country preferred dessert types, while those from the north preferred both dessert and cooking types

Silicon pools, fluxes and the potential benefits of a silicon soil amendment in a nitrogen-enriched tidal marsh restoration

Tidal marshes are important sites of silicon (Si) transformation, where dissolved Si (DSi) taken up by macrophytic vegetation and algal species is converted to biogenic silica (BSi), which can accumulate in the soil, be recycled within the marsh, or be exported to adjacent coastal waters. The role of restored and created tidal marshes in these processes is not well understood, nor is the impact of nutrient enrichment at either the plant or ecosystem level. Here, Si fluxes were examined to develop a Si mass balance in a nitrogen (N)-enriched marsh created with fine-grained dredged material from the Chesapeake Bay, United States. In addition, the effectiveness of Si soil amendments to ameliorate the negative effects of excess nitrogen on Spartina alterniflora was examined through laboratory and field experiments. Silicon was exported to the estuary as DSi (49 g m−2 y−1) and BSi (35 g m−2y−1) in stoichiometric excess of nitrogen and phosphorus. Rapid recycling of Si within both marsh and the tidal creeks appeared to be important in the transformation of Si and export from the marsh. Enhanced macrophyte SiO2 tissue concentrations were observed in the field experiment, with end-of-season mean values of 2.20–2.69% SiO2 in controls and 2.49–3.24% SiO2 in amended plots, among the highest reported for S. alterniflora; however, improved plant fitness was not detected in either experiment. Thus, tidal marshes created with a fine-grained, N-rich dredged material appear to function as a rich source of Si to the restored marsh and local estuarine environment, an overlooked ecosystem service. Soil Si amendments, however, did not appear likely to alleviate N-induced stress in S. alterniflora

Canopy management, leaf fall and litter quality of dominant tree species in the banana agroforestry system in Uganda

Small-scale farmers in the banana-coffee agro-zone of Central Uganda plant andmaintain trees to provide a range of benefits. However, the impact of trees on soil fertility and crop yields is small. On many farms, trees exist in infinite numbers, compositions, with no proper spacing, sequencing and canopy management  recommendations. The objectives of this study were to: quantify and compare leaf fall and leaf litter biomass for the dominant tree species subjected to different pruning regimes and during different seasons and determine the nutrient  concentrations in leaf litter materials in order to assess their potential to improve soil fertility. A survey was conducted on 30 randomly selected farms to examine and  document the tree species. Four tree species were dominant; Ficus natalensis (15.3%), Albizia coriaria (10.2%), Artocarpus  heterophyllus (10.0%) and Mangifera indica (9.2%). Experiments such as canopy pruning, collecting leaf fall and weights of pruned leaf biomass were established for the four dominant trees on five randomly selected farms. A total of 120 trees were subjected to three pruning regimes (0%, 25% and 50%). Litter traps (1 m × 1 m) were placed 2 m from the tree trunk to collect falling leaves. Leaf biomass was collected from pruned branches and eighed. Leaf samples were collected from pruned leaves and a composite sample analysed for carbon and nutrient concentrations. Results showed that 40 tree and shrub species belonging to 21 families existed on farms. Leaf fall was highest in the dry season and A. Heterophyllus registered the highest amount. Leaf biomass from pruned trees was heaviest for M. indica (42.4 ±3 kg) in the wet season and at the 50% pruning regime (45.7± 2.1kg). Total  nutrient concentrations were in the order A. coriaria>F. natalensis>A.heterophyllus>M.indica. We concluded that F. natalensis and A. Coriaria should be integrated more into the agroforestry system to improve soil fertility. A.heterophyllus and M.indica should be planted on farm boundaries. The 50% pruning regime was the best and should be carried out during the wet season.Key words: Tree species, canopy management, leaf fall, nutrient concentrations, soil fertilit

Droughts and the ecological future of tropical savanna vegetation

1. Climate change is expected to lead to more frequent, intense and longer droughts in the future, with major implications for ecosystem processes and human livelihoods. The impacts of such droughts are already evident, with vegetation dieback reported from a range of ecosystems, including savannas, in recent years. 2. Most of our insights into the mechanisms governing vegetation drought responses have come from forests and temperate grasslands, while responses of savannas have received less attention. Because the two life forms that dominate savannas—C3 trees and C4 grasses—respond differently to the same environmental controls, savanna responses to droughts can differ from those of forests and grasslands. 3. Drought‐driven mortality of savanna vegetation is not readily predicted by just plant drought‐tolerance traits alone, but is the net outcome of multiple factors, including drought‐avoidance strategies, landscape and neighborhood context, and impacts of past and current stressors including fire, herbivory and inter‐life form competition. 4. Many savannas currently appear to have the capacity to recover from moderate to severe short‐term droughts, although recovery times can be substantial. Factors facilitating recovery include the resprouting ability of vegetation, enhanced flowering and seeding and post‐drought amelioration of herbivory and fire. Future increases in drought severity, length and frequency can interrupt recovery trajectories and lead to compositional shifts, and thus pose substantial threats, particularly to arid and semi‐arid savannas. 5. Synthesis. Our understanding of, and ability to predict, savanna drought responses is currently limited by availability of relevant data, and there is an urgent need for campaigns quantifying drought‐survival traits across diverse savannas. Importantly, these campaigns must move beyond reliance on a limited set of plant functional traits to identifying suites of physiological, morphological, anatomical and structural traits or “syndromes” that encapsulate both avoidance and tolerance strategies. There is also a critical need for a global network of long‐term savanna monitoring sites as these can provide key insights into factors influencing both resistance and resilience of different savannas to droughts. Such efforts, coupled with site‐specific rainfall manipulation experiments that characterize plant trait–drought response relationships, and modelling efforts, will enable a more comprehensive understanding of savanna drought responses

A raça 4 tropical de Fusaruim oxysporum f. sp. cubense: riscos e impactos potenciais para a bananicultura brasileira.

O surgimento da raça 4 tropical de Fusarium oxysporum f. sp. cubense (FocR4T) tornou a Fusariose da bananeira a maior ameaça da bananicultura mundial. Apesar de FocR4T não ter sido ainda relatada nas Américas, o risco de sua introdução é iminente. Este trabalho objetivou estimar o potencial de riscos e impactos econômicos de uma eventual incursão de FocR4T no Brasil. Foi analisada a distribuição geográfica e impactos causados por FocR4T em nível global, a resistência/susceptibilidade das variedades presentes no Brasil, bem como a capacidade de vigilância e efetividade de barreiras fitossanitárias. Avanços e iniciativas em pesquisa e desenvolvimento também foram analisados. As principais variedades (Prata, Nanica e Maçã) são suscetíveis a FocR4T e até o momento não há variedades resistentes disponíveis. O nível de conscientização sobre FocR4T e a preparação do setor ante um eventual surto da doença são inadequados. Há capacidade de diagnóstico de FocR4T e pesquisas para a obtenção de variedades resistentes e manejo de eventuais surtos da doença estão em curso. Todavia, são necessários mais investimentos para disponibilizar soluções em um prazo menor. É urgente reforçar ações visando a exclusão e detecção precoce de FocR4T no Brasil, bem como elaborar um plano nacional de contingência