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Aspects of the epidemiology of Cassava brown streak disease in Tanzania
No full textIn this study, the field diagnostic survey supplemented with CBSV detection by RT-PCR
using virus coat protein gene-specific primers, revealed the presence of CBSD throughout the
cassava growing areas of Tanzania. Sequence data of 43 CBSV isolates suggested considerable
diversity among although the majority claded together.
CBSV transmission was achieved through cutting tools with 22 % efficiency using test
plants of susceptible cassava cv. Albert. Sap transmission of the virus had 54 % efficiency in cv.
Mreteta. Grafting of CBSV-free susceptible scions onto CBSV-infected rootstocks was the most
efficient transmission technique with up to 100 % recipient plants cv. Albert infected within 4-
weeks after inoculation. The virus was not transmitted through infected root debris or seeds.
Three major types of foliage and root symptoms for CBSD were apparent. The foliage
symptoms included veinal chlorosis, chlorotic blotches and chlorotic spots. The internal root
symptoms were brown necrotic mass, necrotic specks and chalky necrosis in the root cortex. The
nature of occurrence of these symptoms was also elucidated. The tender leaves, youngest
symptomatic leaves and non-necrotic portions of the root cortex were suitable for detection of the
virus by RT-PCR. CBSV-free plants could not be regenerated from CBSV-infected cuttings.
Foliage chloroses were found to be suggestive but not an absolute indication of CBSV
infection. Only 67 % of tested field samples were both symptomatic and infected by the virus; 22
% were CBSV-free despite being symptomatic; 7 % were infected but symptomless; 4 % were
CBSV-free and symptomless.
CBSD incidences and severities in different cultivars varied between seasons and were
dependent on the inherent cultivar characteristics. Foliage and stem CBSD incidences and
severities were significantly (P < 0.001) related to the individual cultivars. The effect of plant age
iv
on CBSD incidences and severities was also significant (P < 0.05). Low temperature (260C day
and 180C night temperature) was critical and lethal to CBSD-affected plants. More than 50 % and
100 % of test plants died within 30 and 50 days respectively, post-exposure to this temperature.
Moisture stress led to deaths of all CBSD-affected test plants within 90 days
Temporal abundance and distribution of rice yellow mottle virus vectors in farmers’ fields in Morogoro, Tanzania
No full textice yellow mottle virus (RYMV), endemic to Africa, is spread
within and between rice fields by several species of Chrysomelid beetles and
grasshoppers. In Tanzania and particularly in Morogoro, the virus is
increasingly becoming a serious problem to rice production. The part of the
field and developmental stage of rice at which RYMV vectors are
predominantly abundant were not known since the need for the study. The
assessment of population abundance of RYMV insect vectors were conducted
in the three divisions of Mngeta, Ifakara and Mang’ula of Kilombero district,
in Morogoro Tanzania using sweep net in 4 m 2 quadrats. Results revealed the
highest abundance of two RYMV vectors, Oxya hyla Serville, 1831 and
Chaetocnema sp, on the border parts of the rice fields rather than in the middle
parts. The study established that the density of RYMV vectors was dependent
on crop growth stages where the number of vectors increased with increase in
crop age and it is concluded that the two insects are the main vectors of
RYMV in the study area
Temporal abundance and distribution of rice yellow mottle virus vectors in farmers’ fields in Morogoro, Tanzania
No full textice yellow mottle virus (RYMV), endemic to Africa, is spread
within and between rice fields by several species of Chrysomelid beetles and
grasshoppers. In Tanzania and particularly in Morogoro, the virus is
increasingly becoming a serious problem to rice production. The part of the
field and developmental stage of rice at which RYMV vectors are
predominantly abundant were not known since the need for the study. The
assessment of population abundance of RYMV insect vectors were conducted
in the three divisions of Mngeta, Ifakara and Mang’ula of Kilombero district,
in Morogoro Tanzania using sweep net in 4 m 2 quadrats. Results revealed the
highest abundance of two RYMV vectors, Oxya hyla Serville, 1831 and
Chaetocnema sp, on the border parts of the rice fields rather than in the middle
parts. The study established that the density of RYMV vectors was dependent
on crop growth stages where the number of vectors increased with increase in
crop age and it is concluded that the two insects are the main vectors of
RYMV in the study area
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
Relationship between symptoms expression and virus detection in cassava brown virus streak-infected plants
No full textJournal ArticleDiagnosis of Cassava brown streak disease (CBSD) has for long been based on foliar and root symptoms
expression on infected plants. Variability in patterns of symptoms expression between varieties and seasons
however, has meant that symptom-based diagnostics are unreliable. The current study established the relationship
between symptom expression on cassava plants and the infection with Cassava brown streak virus (CBSV) using
RT-PCR diagnostic tool. It was established that manifestation of CBSD-like symptoms (particularly the foliar
chloroses and necrotic blotches) may not be an absolute indication of CBSV-infection. Only 67% of tested samples
were both foliarly symptomatic and infected by the virus. About 22% of samples were free from CBSV despite
being foliarly symptomatic and 7% were CBSV-infected but foliarly symptom less. Some CBSV-infected plants
did not exhibit any foliar symptoms although had root necroses. A few CBSV-free plants were regenerated from
infected cuttings in one of the four tested cultivars, Albert. Five out of fifteen (33%) plants cv. Albert were
symptom less and two out of the five (40%) were CBSV-free. The findings from this study suggest that
symptoms-based diagnosing for CBSV infections is unreliable. As some of CBSV-infected plants tend to be
considered CBSV-free due to lack of the disease symptoms, the scenario might have contributed to unlimited
spread of CBSD through latently-infected planting materials
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
Occurrence of the entomopathogenic Fungi of Spodoptera frugiperda (Lepidoptera: Noctuidae) in selected areas of Tanzania
Get PDFSpodoptera frugiperda (J.E. Smith) is a highly destructive pest that affects major food and cash crops in Sub-Saharan Africa. Maize, in particular, is a preferred host for this pest, posing a significant threat to food security. Initially, conventional synthetic pesticides were widely used to combat the pest. However, the potential of entomopathogenic fungi (EPF) as cost-effective and safe alternative has been recognized. The objective of this study was to collect and identify the local EPF species in selected areas of Tanzania\u27s mainland, namely Mwanza, Morogoro, Coast, and Songwe regions. Morphological and molecular methods were employed to identify the fungal species recovered from 100 S. frugiperda cadavers. The findings revealed that 90% of the recovered fungi belonged to the genera of Fusarium while the remaining 10% were Clonostachys. These results suggest that Fusarium species hold promise as effective bio-control agents against S. frugiperda due to their wide distribution and tolerance to field disturbances. However, additional studies are necessary to validate the effectiveness of these recovered fungi against S. frugiperda
Relationship between symptoms expression and virus detection in cassava brown virus streak-infected plants
No full textJournal ArticleDiagnosis of Cassava brown streak disease (CBSD) has for long been based on foliar and root symptoms
expression on infected plants. Variability in patterns of symptoms expression between varieties and seasons
however, has meant that symptom-based diagnostics are unreliable. The current study established the relationship
between symptom expression on cassava plants and the infection with Cassava brown streak virus (CBSV) using
RT-PCR diagnostic tool. It was established that manifestation of CBSD-like symptoms (particularly the foliar
chloroses and necrotic blotches) may not be an absolute indication of CBSV-infection. Only 67% of tested samples
were both foliarly symptomatic and infected by the virus. About 22% of samples were free from CBSV despite
being foliarly symptomatic and 7% were CBSV-infected but foliarly symptom less. Some CBSV-infected plants
did not exhibit any foliar symptoms although had root necroses. A few CBSV-free plants were regenerated from
infected cuttings in one of the four tested cultivars, Albert. Five out of fifteen (33%) plants cv. Albert were
symptom less and two out of the five (40%) were CBSV-free. The findings from this study suggest that
symptoms-based diagnosing for CBSV infections is unreliable. As some of CBSV-infected plants tend to be
considered CBSV-free due to lack of the disease symptoms, the scenario might have contributed to unlimited
spread of CBSD through latently-infected planting materials
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