Survey of cassava virus diseases in Tanzania

Legg, J.P.; Raya, M. D.

doi:10.1080/096708798228473

Cited by 70 publications

(60 citation statements)

References 7 publications

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“…This suggests that the same information would be obtained when either diagonal or zigzag method was used for CBSD diagnosis. Although the diagonal method has been previously preferred by some workers in CBSD survey [10,11], the findings in the current study suggest that the zigzag method may also be used to produce similar results. The fact that there were high correlation values (r > 0.9) between diagonal and zigzag methods on CBSD incidences and severities obtained, suggests that CBSD affected plants were somewhat uniformly distributed across the assessed fields.…”

Section: Comparison Of Methods For Field Traversingsupporting

confidence: 63%

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Approaches to diagnosis and detection of cassava brown streak virus (<i>potiviridae: ipomovirus</i>) in field-grown cassava crop.

Rwegasira¹,

Rey²,

Nawabu³

2011

African Journal of Food, Agriculture, Nutrition and Development

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Cassava brown streak disease (CBSD) has been a problem in the East African coastal cassava growing areas for more than 70 years. The disease is caused by successful infection with Cassava Brown Streak Virus (CBSV) (Family, Potyviridae: Genus, Ipomovirus). Diagnosis of CBSD has for long been primarily leaf symptoms-based. This is unreliable due to the irregular pattern and variability of the disease phenotype in roots and leaves. The suitable method to undertake reliable field diagnostic survey and derive acceptable analysis of the disease situation has never been standardized. Zigzag and diagonal approaches for disease assessment have been used successfully on other diseases infecting cassava such as Cassava mosaic disease but neither of them has ever been tested and proven suitable for CBSD assessment. In addition, the suitable sample for successful molecular detection of the causal virus has never been optimised. The number of samples to be collected from large plant stands which would be a true representation of the population has never been determined. The effect of sample bulking on possible detection or non detection of infection particularly when un-infected samples are combined with infected ones is not known. In this study, the comparative efficiencies of diagonal and zigzag approaches to CBSD field diagnosis were tested through surveys conducted in 20 randomly selected farmers' fields in major cassava growing areas of the Coastal and Lake Zones in Tanzania. Using molecular diagnostic techniques, the plant parts which are suitable for Cassava brown streak virus (CBSV) detection were determined. Sample bulking was tested for rationalized laboratory detection of CBSV over large cassava stands. The study revealed that CBSD incidences and severities obtained using either diagonal or zigzag approach did not differ significantly. Suitable parts for CBSV detection were identified to be flowers, fruits, apical buds, young tender leaves, newly-opened leaves, youngest symptomatic leaves, the tender top-green portion of the stem and non-necrotic storage root tissues. CBSV was not detected in seeds. In bulked leaf samples, CBSV was detected from ratios of 1:1 up to 1:19 of CBSVinfected to CBSV-free tissues in cultivar Albert. It was concluded that either zigzag or diagonal can be used for CBSD field diagnosis. A choice of the suitable sample is of absolute necessity, and bulking of many samples for collective CBSV detection over a large crop stand is effective.

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Section: Comparison Of Methods For Field Traversingsupporting

confidence: 63%

“…However, the standard approaches to field diagnosis of CBSD are not yet established. The diagonal method of field traversing has been commonly used to assess the field incidences and severities of CBSD in farmers' fields [10,11]. This method has also been used in field assessment of cassava mosaic virus disease [12].…”

Section: Introductionmentioning

confidence: 99%

Approaches to diagnosis and detection of cassava brown streak virus (<i>potiviridae: ipomovirus</i>) in field-grown cassava crop.

Rwegasira¹,

Rey²,

Nawabu³

2011

African Journal of Food, Agriculture, Nutrition and Development

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“…There was a clear relationship between whitefly abundance and whitefly-borne infection, as has been demonstrated from studies conducted elsewhere in Africa (Legg and Raya, 1998). However, such relationships are often difficult to substantiate due to the high degree of temporal variability in whitefly populations (Fishpool et al, 1995), and the latent period of 3-5 weeks between transmission and first symptom expression (Fargette et al, 1993).…”

Section: Discussionmentioning

confidence: 75%

Incidence and severity of cassava mosaic disease in the Republic of Congo

Ntawuruhunga¹,

Okao-Okuja²,

Bembe³

et al. 2010

African Crop Science Journal

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Diagnostic surveys were conducted in 2002 and 2003 in order to provide a comprehensive and detailed assessment of the status of cassava mosaic disease (CMD) in the Republic of Congo (ROC) and to determine if the disease was spreading. In 2002, 105 farmers' fields were assessed in the four major cassava-producing regions of the country. In 2003, 163 fields were sampled in nine regions and Brazzaville Commune. Incidence of cassava mosaic disease was generally high, averaging 80 and 86 % for 2002 and 2003, respectively; while damage was moderate to severe. In 2002, disease incidence was moderate in Pool (73%) but high in Brazzaville (81%), Cuvette Centrale (82%) and in Plateaux Region (84%). Pool region still had the lowest incidence (78%) in 2003, while Sangha (95%) had the highest incidence. The greatest disease severity was recorded in Niari region in the south and Cuvette Ouest region in the north in 2003. East African cassava mosaic virus Uganda variant (EACMV-UG) occurred virtually throughout the country, commonly in dual infections with African cassava mosaic virus. The high incidence of disease in plants considered to be the results of cutting infection (74% in 2002 and 82% in 2003), relatively low incidence of disease in plants considered to be infected by whiteflies and wide distribution of EACMV-UG points to the fact that the CMD pandemic is a chronic in the country and the areas sampled are currently in a stable post-epidemic phase. This situation is comparable to that in areas of East Africa affected by a pandemic during the 1990s, including Uganda, parts of western Kenya and north-western Tanzania. These findings clearly verify the assertion that the CMD pendemic has expanded across Central Africa and provide a basis for designing interventions and control strategies for the entire region. dans la région du Pool demeurait encore plus faible (78%) en 2003 pendant que Sangha avait l'incidence plus élevée (95%). En 2003 la plus grande gravité de la maladie était enregistrée dans la région de Niari au Sud et dans la région Ouest de la cuvette au Nord. La variante du virus de la mosaïque du manioc de l'Afrique de l'Est en Ouganda (VVMMAEO) s'était virtuellement manifestée à travers le pays; les infections s'étaient couplées avec le virus de la mosaïque du manioc africain. La grande incidence de la maladie des plantes considérée être les résultats de la contagion des boutures était de 74% en 2002. Relativement, la basse incidence dans les plantes considérées être contaminées par les mouches blanches et la grande part du VVMMAEO était de 82% en 2003. Ceci a abouti à la conclusion selon laquelle la pandémie de la MMM avait contaminé le pays quelques années auparavant et que les régions ayant fait l'objet de l'échantillon sont actuellement dans une phase post-endémique. Cette situation est comparable à celle des régions de l'Afrique de l'Est qui étaient contaminées par une pandémie les années 1990 y compris l'Ouganda, les parties Ouest du Kenya et le Nord-Ouest de la Tanzanie.

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“…The first systematic countrywide assessment of CBSD was completed in 1994 in Tanzania (Legg & Raya, 1998) (Legg & Raya, 1998). However, the view that CBSD is a lowland disease remained unchanged until 2004, when the first report was made of significant spread of CBSD in central/southern Uganda (Alicai et al, 2007).…”

Section: Current Status Of Cbsd In Africa and Effects On Yieldmentioning

confidence: 99%