Physiological characteristics of Microcyclus ulei (P. Henn.) V.ARX. – a fungal pathogen of the cyanogenic host Hevea brasiliensis

The ascomycete Microcyclus ulei causes premature leaf shedding of the rubber tree, Hevea brasiliensis. During the development of this biotrophic fungus in the tissues of infected leaves HCN is liberated from the lesions. Despite high HCN concentrations in the leaf tissue the pathogenic fungus develops infection hyphae. The reaction of M. ulei to hydrogen cyanide and the biochemical properties of a fungal β-glucosidase which is active on the cyanogenic precursors of the host plant are reported.

Agroecological profile of plants used as production factors and as management components in tropical polyculture systems.

Polyculture plantings enriched by controlled growth of secondary vegetation after slash and burn treatment are suitable systems for recuperation of degraded areas in Central Amazonia. In order to adapt polycultures to their indivicual sites, predominantly indigenous useful plants have to be combined. These plants act as production factors and as site management components. There is urgent need to study the inherent ecological adaptability and phenotype flexibility of these plants, their specific nutrient needs, their reaction to environmental factors and their impact on their specific sites in order to work out rational combinations of plants for resistant and resilient polyculture systems. The development of a descriptor system for polyculture system plants is on its way. The results of the SHIFT Projects ENV 23, 23/2, 42, 45, and 52 contribute to this descriptor system

Sustainable land use systems in Central Amazon rain forests.

Development of the multiple cropping systems wich are ecologically, socially and economically viable for the humid tropics by rising and stabilizing the using the areas for a long period of time. The strategic aim the project is to reduce clearing and burning of primary forests and to reduce the rural-to-urban migration in the central Amazon (Brasil)

Structure and function of the seed coat of Theobroma cacao L. and its possible impact on flavour precursor development during fermentation

Seed coats are known to regulate the transfer of substances between the embryo and both the mother plant and the environment. The permeability of the seed coat of the fermenting seeds of Theobroma cacao may significantly affect its final flavour quality. Many studies suggest that the flavour quality is genetically determined and uniform within one clone. This implies that the flavour quality can only be inherited exclusively from the mother plant. Consequently, factors affecting flavour quality should be located in the maternal tissues surrounding the seed. As only the fruit pulp and the seed coat are exclusively maternal in origin, whereas the embryo and the endosperm are the progeny of both parents, the flavour quality may be associated with transport characteristics of the seed coat. In this context the influence of the seed coat on the transport of acetic acid, the main product of fermentation is of high relevance.We investigated the transport characteristics of the seed coat of T. cacao with modern light- and fluoroscence microscopic methods. Tracers were used in order to evaluate the potential impact of structures such as barriers and entry sites for the transport of water and solutes. Our morphological, histochemical and microspectrophotometrical data and the interpretation of the tracer distributions demonstrate that certain structures of the seed coat strongly influence the course of transport processes in the mature seed coat of T. cacao. These include the inner contact zone of fruit pulp and seed coat, hilum, sclereid layer, hypostase, micropyle and endosperm cuticle. Under natural conditions these structures may prevent desiccation and loss of nutrients of the recalcitrant seed. During fermentation the mentioned structures appear to affect the influx of acetic acid, in analogy to water and solutes. Insufficient or excessive acidification impedes sufficient formation of flavour precursors resulting in a flat or acid taste. Asynchronous and uneven infiltration of acetic acid into the cotyledon cells will lead to inconsistent and suboptimal flavour quality. In conclusion we suggest that flavour quality of the fermented seeds is predominantly due to transport kinetics of water and solutes during the fermentation process rather than a reflection of genetically coded differences in storage proteins

Polyphenol oxidase (PPO, catecholase) activity during germination and early seedling growth of Cicer milkvetch (Astragalus cicer L.)

Mature seeds of the legume Astragalus cicer L. form a homogeneous seed pool in size and weight. They occur either brown coloured or yellow coloured. They reveal an expressed dormancy but they germinate readily after mechanical scarification. Time span of germination and early seedling development under defined conditions were followed and compared to the activity and potential activation of polyphenol oxidase (PPO, catecholase). The yellow seeds developed without difficulties, but on the brown coloured seeds in the course of germination hyphal growth was visible which was linked with the death of the seedlings. Quantitative experiments with the yellow seeds revealed that scarified seeds formed more than 98 % of seedlings within seven days. There was no difference of germination rate between dark and daylight incubations. The polyphenol oxidase of the seeds occurs in two forms, a preformed testa localized enzyme and an induced PPO activity of the seedling. The initially high activity of the testa related PPO (1.32 μM O2/h x g fresh weight) decreases during the first days after germination, the activity of the seedling related PPO becomes detectable four to five days after onset of germination. After seven days the activity in roots is about 3.6 μM O2/h x g fresh weight. The cotyledons reveal 2.3 and the hypocotyl 1.9 μM O2/h x g fresh weight, respectively.There is an indication that autoinhibitory components interfere with the germination process. The importance of the polyphenol oxidase as a component of the plants’ protection system during germination is discussed

Germinação de conídios de Microcyclus ulei e sua sensibilidade a fungicidas, "in vitro".

Estudou-se a germinação de conídios de Microcyclus ulei, agente causal do mal-das-folhas da seringueira, em tubos de ensaio de 5mm de diâmetro e placas de Petri de 32mm de diâmetro

Characteristics of sustainable polyculture production systems on terra firme.

The combination of soil science, forestry, agronomy and biology allowed an analytical comparison of various experimental mixed culture systems. From these studies, a descriptor system was developed which allows to understand the contribution of each plant species to nutrient cycling, water distribution, litter formation, overall biomass production and crop production. This knowledge allows to combine plants so that their properties interact to form a system, which minimizes mineral losses and which regulates air humidity and water distribution and thus leads to stable crop production. The general conclusion which can be drawn after eight years of polyculture study is: a) stable productions systems for samllholder families have bee developed; b) the systems are variable; they can be adapted to the respective site conditions; c) the manager of these plantations requires a deeper understanding of the cultivation systems and an intensive dissemination of knowledge and a well develope on-farm training system for farmers

Utilization of abandoned areas in Amazonia by polycultures of perennial useful plants.

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Spatial and temporal change of the spontaneous vegetation in an agricultural fields experiment.

The objective of the SHIFT field trial carried out on an area of 17 ha at the experimental site of EMBRAPA Amazônia Ocidental near Manaus, Amazonas, Brazil, is to try out the reuse of an abandoned agricultural site by mixed cropping systems and to survey some of the most important ecological interactions between the growth of the useful plants, the spontaneous vegetation in the field, and management and site factors