Infection of the cones and seeds of Welwitschia mirabilis by Aspergillus niger var. phoenicis in the Namib-Naukluft Park

AbstractWelwitschia mirabilis Hook. fil. is a unique and rare dioecious desert gymnosperm endemic to the Namib Desert. The female plants bear 90–100 megasporophylls, of which 50–60% may be fertile, but up to 80% of those fertile seeds may be infected by Aspergillus niger var. phoenicis. This contamination results in seed and seedling death, potentially negatively affecting recruitment of plants into the population.The pattern of infection of the cones and seeds in the field was studied over a period of eight months at the Hope Mine in the Namib-Naukluft Park. Infection of the cones was found to peak coincident with the appearance of the pollination drops, and with high temperatures, winds and significant rainfall. W. mirabilis cones were microscopically examined and spores of A. niger var. phoenicis were found embedded in the dehydrating pollination drop at the tip of the micropyle, suggesting that this was one of the routes by which the seeds were infected. The heteropteran, Probergrothius sexpunctatis, was also implicated in the infection of the seeds, since it was found to be carrying spores of A. niger var. phoenicis and was observed feeding on mature seeds and immature cones. While most post-harvest treatments have proved ineffective in eradicating A. niger var. phoenicis from the seeds, promising results are presently reported using a fungicide containing tebuconazole as the active ingredient

Seed germination of valuable high-altitude medicinal plants of southern Africa

Germination of nine important medicinal plant species from the high altitudes of southern Africa was investigated in relation to different environmental parameters. The seeds were subjected to different constant and alternating temperatures, temperature shifts, light and dark conditions, and cold stratification periods. Temperature regimes of 17-23°C appear most suitable for optimal germination for all the species examined. In some species, a temperature shift from 10°C to 20°C and 30°C to 20°C improved the final percentage germination. In the majority of the species investigated, exposure of seeds to continuous or alternating light significantly promoted germination over continuous dark. However, no phytochrome effect was determined. Tulbaghia alliacea and Dianthus basuticus germinated equally well in light and dark, while Urginea capitata responded significantly to the continuous light treatment. In some species, cold stratification stimulated germination and reduced the mean germination time

Observations on in vitro behaviour of the zygotic axes of fluted pumpkin

Fluted pumpkin, Telfairia occidentalis Hook. f., is an important leaf and seed vegetable and a local medicinal plant across West Africa. Many biological constraints have become potent threats to the existence of the plant necessitating an urgent need to collect and conserve the existing narrow genetic diversity. However, conservation by seed storage is impossible because the seed is recalcitrant, that is desiccation- and chilling-sensitive. Micropropagation is the only immediate alternative option for the conservation of fluted pumpkin germplasm. In order to facilitate this, the behaviour of excised embryonic axes and shoot tips of fluted pumpkin under in vitro conditions were investigated. Systemic infection of seeds from field led to frequent and high microbial contamination in culture. There was interaction between the type of microbial contamination and the storage environment of seeds prior to excision of the axes. Axes greened under low light intensity and root growth was dependent on the orientation of the axes. In general, zygotic axes of the plant are easy to grow in vitro under a range of nutrient media and culture condition

Forest tree seed health for germplasm conservation

The conservation and use of forest genetic resources worldwide poses several challenges to scientists, policy-makers and, in particular, to local stakeholders interested in long-term strategies to manage these biological resources in a sustainable manner. The vast diversity of tree species, many of which are still unknown, the high level of threats and the increased demand for forest products require prioritization of actions, clear indications for research and development, and strategies to mitigate the current trends in the depletion of forest resources. The strategy of conservation 'through-use' of forest genetic resources is a very important alternative to an in situ approach and, as such, is to be promoted and developed. However, basic knowledge and understanding of species' reproductive biology, seed production, seed quality and health aspects, limit the use of a larger number of species in important activities such as restoration, rehabilitation, agroforestry and on-farm conservation practices. Increasingly, the use of forest genetic diversity in research and breeding requires a greater movement of germplasm. This technical bulletin, prepared by Drs J. R. Sutherland, M. Diekmann and P. Berjak, all well-known scientists in their respective areas of specialization, aims to breach some of the knowledge gaps in forest seed biology and technology and, more importantly, to contribute to future research on priority forest seed health aspects. In addition, this it aims to increase awareness amongst technical staff involved in conservation and use activities. To this end it presents state-of-the-art tools for the identification of the most important tree seed pathogens and provides clear and ready-touse molecular-based tools for the screening of fungi and virus in seeds

The Re-Establishment of Desiccation Tolerance in Germinated Arabidopsis thaliana Seeds and Its Associated Transcriptome

The combination of robust physiological models with “omics” studies holds promise for the discovery of genes and pathways linked to how organisms deal with drying. Here we used a transcriptomics approach in combination with an in vivo physiological model of re-establishment of desiccation tolerance (DT) in Arabidopsis thaliana seeds. We show that the incubation of desiccation sensitive (DS) germinated Arabidopsis seeds in a polyethylene glycol (PEG) solution re-induces the mechanisms necessary for expression of DT. Based on a SNP-tile array gene expression profile, our data indicates that the re-establishment of DT, in this system, is related to a programmed reversion from a metabolic active to a quiescent state similar to prior to germination. Our findings show that transcripts of germinated seeds after the PEG-treatment are dominated by those encoding LEA, seed storage and dormancy related proteins. On the other hand, a massive repression of genes belonging to many other classes such as photosynthesis, cell wall modification and energy metabolism occurs in parallel. Furthermore, comparison with a similar system for Medicago truncatula reveals a significant overlap between the two transcriptomes. Such overlap may highlight core mechanisms and key regulators of the trait DT. Taking into account the availability of the many genetic and molecular resources for Arabidopsis, the described system may prove useful for unraveling DT in higher plants