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

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

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

Seed degeneration of banana planting materials: strategies for improved farmer access to healthy seed

Vegetatively propagated crops suffer from yield loss and reduced stand density and longevity caused by the build‐up of certain pests and pathogens between successive plantings via infected planting material. Here, six seedborne phytosanitary problems of banana are reviewed to evaluate whether a seed degeneration framework is a useful tool to identify approaches to achieve healthier planting materials. Phytoparasitic nematodes and weevils generate gradual declines in yields and in sucker health. Fusarium wilt and banana bunchy top virus cause progressive mat collapse across the field. Symptomless suckers from any mat in infested fields represent a risk of transmitting the disease to a new field. Xanthomonas and ralstonia wilts, due to incomplete systemicity, are intermediate in their threat to yield loss and frequency of transmission in suckers. Losses to banana streak virus are triggered by abiotic stress, although sucker transmission of episomal banana streak virus also contributes. A qualitative equation described here for seed degeneration covers a cycle beginning with the quality and risk factors of the planting material used to plant a new field and ends with the quality and risk factors of the suckers extracted from the field to plant a new field. This review of five planting material multiplication methods commonly used in banana contrasts their differing usefulness to address seed degeneration in the small farm context. It is proposed that initiatives to offset banana seed degeneration should integrate the role of off‐farm actors into decentralized initiatives rather than attempt to duplicate national seed certification frameworks from other true seed or vegetatively propagated crops

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

Fusarium wilt of banana: Current knowledge on epidemiology and research needs toward sustainable disease management

Banana production is seriously threatened by Fusarium wilt (FW), a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). In the mid-twentieth century FW, also known as “Panama disease”, wiped out the Gros Michel banana industry in Central America. The devastation caused by Foc race 1 was mitigated by a shift to resistant Cavendish cultivars, which are currently the source of 99% of banana exports. However, a new strain of Foc, the tropical race 4 (TR4), attacks Cavendish clones and a diverse range of other banana varieties. Foc TR4 has been restricted to East and parts of Southeast Asia for more than 20 years, but since 2010 the disease has spread westward into five additional countries in Southeast and South Asia (Vietnam, Laos, Myanmar, India, and Pakistan) and at the transcontinental level into the Middle East (Oman, Jordan, Lebanon, and Israel) and Africa (Mozambique). The spread of Foc TR4 is of great concern due to the limited knowledge about key aspects of disease epidemiology and the lack of effective management models, including resistant varieties and soil management approaches. In this review we summarize the current knowledge on the epidemiology of FW of banana, highlighting knowledge gaps in pathogen survival and dispersal, factors driving disease intensity, soil and plant microbiome and the dynamics of the disease. Comparisons with FW in other crops were also made to indicate possible differences and commonalities. Our current understanding of the role of main biotic and abiotic factors on disease intensity is reviewed, highlighting research needs and futures directions. Finally, a set of practices and their impact on disease intensity are discussed and proposed as an integrative management approach that could eventually be used by a range of users, including plant protection organizations, researchers, extension workers and growers