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Seed-borne Fusarium pathogens in agricultural crops
Get PDFISHS Acta Horticulturae 1204: VII International Symposium on Seed, Transplant and Stand Establishment of Horticultural Crops - SEST2016.Diseases caused by Fusarium spp. occur worldwide throughout all production areas of edible and ornamental plants as well as tree plantations. Fusarium spp. cause yield losses of up to 80% in both field- and greenhouse-grown crops, resulting in serious economic losses. It is known that plant material such as fruits and seeds as well as soil, can be a pathway of disease transmission; therefore, different strategies to control Fusarium have been used e.g., planting new cultivars, grafting, using inorganic and organic substrates, soil solarization, biofumigation and seed treatments. Nonetheless, new Fusarium pathotypes are often detected or reported to be the causal agents of diseases. To determine the pathway of Fusarium transmission, specifically through seed, is challenging and scientific reports in this regard are lacking. To prove that seed is the pathway of pathogen transmission is time-consuming and laborious, since pathogenicity tests with several Fusarium isolates must be conducted during several growth stages of the host. The isolates then have to be re-isolated from infected plant parts to confirm Koch's postulates and seeds from inoculated plants need to be obtained which in turn need to be tested again for the presence of the pathogen. To prevent the introduction and distribution of Fusarium spp., growers (for local and export markets), technical advisors, and seed producers need to use disease-free seed. The potential production of Fusarium mycotoxins during storage is an additional concern when using Fusarium infected seeds for food. Depending on the region, it is important to know which crops (hosts) are susceptible to a particular Fusarium sp., how this pathogen can be avoided, and how to produce and select healthy fruits and seeds. Efforts must be directed towards avoiding seed contamination with pathogens and developing or optimizing seed health testing methods to detect Fusarium.http://www.actahort.org2019-06-01hj2019Forestry and Agricultural Biotechnology Institute (FABI)Plant Production and Soil Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The effect of traditional storage methods on germination and vigour of maize (Zea mays L.) from northern KwaZulu-Natal and southern Mozambique
Get PDFIn Sub-Saharan Africa, maize (Zea mays L.) is one of the most nutritional crops and proper storage of seeds continues to be a challenge for subsistence farmers. Storage fungi, which reduce seed quality, become active in seeds when moisture levels are 14% or higher and this is influenced by the way seeds are stored. The aim of the present study was to test germination and vigour of maize seeds that were subjected to traditional storage during 2005 and to test germination of the maize seeds after storage for one year under conditions of fluctuating temperature. A preliminary survey was conducted and maize samples (white and yellow) were collected from small-scale subsistence farmers in northern KwaZulu-Natal (South Africa) and Mozambique. Seeds that were left in the field to dry and seeds that were commercially treated with Celest® XL served as controls. Germination was measured according to the International Seed Testing Association (ISTA) rules. The maize that was left in the field (NHS) to dry gave 100% germination in 2005. The treated control had a germination of 94.0%. Seeds that were imbibed for 40 h had the highest percentage weight increase following rapid imbibition but four of the six samples maintained germination above 70% following slow imbibition. The conductivity of the solute was read following imbibition. Field stored maize had the lowest solute leakage (1181 μS) and this correlated with the high percentage seeds with living tissue as indicated by the tetrazolium staining following rapid (94.4%) and slow (95.8%) imbibition. The number of fungi isolated from the samples reflected the initial condition of the samples with the fungicide treated control having the lowest percentage infection (11%), NHS had 33% and yellow maize that was stored on the cob and had with insect damage (SIH) had the highest, namely 71%. After the first set of experiments, samples were stored at 26–28 °C to simulate the fluctuating original storage conditions. A year later the samples were subjected to the standard germination test. The decline in seed viability during the storage period was exhibited by results of the standard germination test. Maize that was left in the field had a 74.7% decrease in germination while the sample stored in potato bag (PHEL) and the treated control maintained germination above 80%. Two of the six samples failed to germinate. This study also showed that fungicide seed treatment is a viable option to maintain viability of the seeds, especially when the maize is to be stored until the next season
Fungi associated with Aizoaceae seed in the Succulent Karoo
Get PDFISHS Acta Horticulturae 1204: VII International Symposium on Seed, Transplant and Stand Establishment of Horticultural Crops - SEST2016.The Aizoaceae, commonly known as mesembs or “ice plants”, is a plant family endemic to Namaqualand, an area inside the Succulent Karoo biodiversity hotspot in South Africa. The more than 1800 unique mesembs are in part characterised by their hygrochastic seed capsules dispersing their seed by jet action. Six capsule types: Mesembryanthemum-, Delosperma-, Drosanthemum-, Lampranthus-, Ruschia- and Leipoldtia-type are distinguished by differences in funicles, covering membranes and closing bodies. With the existence of microbial endemism, now widely recognised, research into community ecology in the Succulent Karoo is needed to enable proper conservation. Sadly the microbial life associated with Aizoaceae has received little attention, Alternaria, Colletotrichum and Fusarium, have however been isolated from the halophyte Sesuvium portulacastrum, one of the few species from Aizoaceae but not endemic to South Africa. Fungi are known to aid in germination, seedling establishment, growth, water relations and nutrition in the Cactaceae (a family closely related to Aizoaceae). We believe that fungi may play a role in the ability of Aizoaceae to thrive in Namaqualand due to their specialization in the form of thick-walled spores that remain viable and have the ability to grow slow even at extreme aridity. We have isolated species of Alternaria, Aspergillus, Bipolaris, Cladosporium, Fusarium and Talaromyces from seeds of common mesemb species from Namaqualand. This is the first report of fungi associating with the specialised propagative material of Aizoaceae.http://www.actahort.org2019-06-01hj2019Forestry and Agricultural Biotechnology Institute (FABI)Plant Production and Soil Scienc
Screening of plant extracts for antifungal activities against Colletotrichum species of common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata (L.) Walp)
Get PDFThe aim of the present investigation was to evaluate the antifungal activities of plant extracts which can be used to
control bean and cowpea anthracnose. Acetone, ethyl acetate and water extracts of Ipomoea batatas, Carica
papaya, Allium sativum, Syzygium cordatum, Chlorophytum comosum and Agapanthus caulescens were
screened in vitro for their antifungal activities against Colletotrichum lindemuthianum and Colletotrichum
dematium of common bean and cowpea using the agar disc infusion and microtitre double-dilution techniques.
The same extracts were then tested for antifungal activity in vivo as seed treatments against anthracnose disease.
The water extracts of Carica and Syzygium were active against C. lindemuthianum and had minimum inhibitory
concentrations (MICs) of 1·56 mg/ml. Syzygium, Allium and Chlorophytum water extracts were active against
C. dematium and MICs were 3·13, 6·25 and 12·5 mg/ml, respectively. The MICs of Allium, Syzygium and
Agapanthus acetone extracts were 0·78, 3·13 and 6·25 mg/ml, respectively, against C. lindemuthianum and 0·78,
6·25 and 3·13 mg/ml against C. dematium. Agapanthus water extracts and all the acetone extracts tested in vivo
effectively reduced the incidence and severity of bean anthracnose disease in the greenhouse. Agapanthus
acetone, Allium water, and both acetone and water extracts of Carica and Syzygium performed well in vivo in
reducing cowpea anthracnose disease and compared well with reductions due to the application of the synthetic
fungicide fludioxonil+mefenoxam (the commercial product Celest® XL) applied at 25 gai/l and also with levels
in the non-inoculated control. The Agapanthus, Carica, Syzygium and Allium extracts were active on both
Colletotrichum spp. in vitro and also reduced anthracnose disease of bean and cowpea and are potential seed
treatments in anthracnose disease control. The easy seed treatment process and the accessibility of plants used in
the present study could lead to high adoption of the use of the plant extracts as seed treatments by resource-poor,
smallholder farmers.http://journals.cambridge.org/action/displayJournal?jid=AGSam201
Occurrence and distribution of cowpea damping-off and stem rot and associated fungi in Benin
No full textDamping-off and stem rot of cowpea is an important soil-borne disease worldwide. Cowpea fields were randomly chosen in each agro-ecological zone in Benin and surveyed in 2001 and 2002 to determine the occurrence of the diseases throughout the country. Diseased plants, prevailing environmental conditions and cowpea grower cultural practices were recorded and causal agents associated with the disease identified. Results indicated that damping-off and stem rot were distributed throughout Benin. The disease incidence was higher in the South (0·074) and Centre zones (0·063) than in the other zones (<0·02) in the country. Among factors influencing the disease incidence, cultural practices such as sole crop and no-till systems appeared to be most important. Isolated fungi included Sclerotium rolfsii, Fusarium spp., Pythium ultimum, Rhizoctonia solani, Phoma sp., Rhizopus sp. and Trichoderma harzianum. None of the Fusarium, T. harzianum or Rhizopus sp. isolates were pathogenic in the greenhouse. Pythium ultimum, R. solani and Phoma sp. were infrequently isolated and few isolates caused the disease symptoms in the greenhouse. However, this is the first report of Phoma sp. causing damping-off and stem rot of cowpea in Benin. Sclerotium rolfsii was by far the most common species isolated from all the agro-ecological zones and all isolates were pathogenic on cowpea in the greenhouse. Sclerotium rolfsii was considered to be the main causal agent of cowpea damping-off and stem rot in the Republic of Benin due to its wide distribution, high incidence and predominance on plants with damping-off and stem rot symptoms
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