Abstract
Cassava brown steak disease (CBSD), caused by Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), is the most important biotic constraint to cassava production in East and Central Africa. Concerted efforts are required to prevent further spread into West Africa as well as to reduce losses in areas already affected. The study reported here was part of a five-country (Kenya, Malawi, Mozambique, Tanzania and Uganda) programme that aimed to identify superior cassava cultivars resistant to CBSD and to disseminate them widely in the region. Seventeen tissue-cultured and virus-tested cultivars were evaluated in Tanzania across nine sites with diverse CBSD inoculum conditions. Experiments were planted using an alpha-lattice design and assessments were made of surrounding inoculum pressure, CBSD foliar and root incidence and root yield at harvest. There were large differences in CBSD infection between sites, with greatest spread recorded from the north-western Lake (Victoria) zone. Differences were driven by Bemisia tabaci whitefly vector abundance and CBSD inoculum pressure. Both CBSV and UCBSV were almost equally represented in cassava fields surrounding experimental plots, although CBSV predominated in the north-west whilst UCBSV was more frequent in coastal and southern sites. However, the incidence of CBSV was much greater than that of UCBSV in initially virus-free experimental plots, suggesting that CBSV is more virulent. Cultivars could be categorised into three groups based on the degree of CBSD symptom expression in shoots and roots. The seven cultivars (F10_30R2, Eyope, Mkumba, Mkuranga1, Narocass1, Nase3 and Orera) in the most resistant category each had shoot and root incidences of less than 20%. Fresh root yield differed between sites and cultivars, but there was no genotype by environment interaction for this trait, probably attributable to the large fertility and soil moisture differences between sites. Susceptible cultivars and the local check performed well in the absence of CBSD pressure, highlighting the importance of exploiting quality and yield traits of local landraces in breeding programmes. Overall, our results emphasized the importance of applying a balanced strategy for CBSD management. This should use both improved and local germplasm resources to generate high yielding cultivars for specific end-user traits, and combine the deployment of improved cultivars with phytosanitary control measures including the use of healthy planting material and planting during periods of reduced CBSD infection.
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Claims 10
Claim · model-written summary
CBSD infection varied substantially between sites, with greatest spread in the north-western Lake zone.
- Taxon
- cassava
Manihot esculentat0 - Outcome
- CBSD infectione0
- Setting
- north-western Lake (Victoria) zonee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There were large differences in CBSD infection between sites, with greatest spread recorded from the north-western Lake (Victoria) zone.”
t0“cassava”
Claim · model-written summary
Whitefly abundance and inoculum pressure drove site differences.
- Taxon
- cassavaManihot esculentat0
- Interactor
- Bemisia tabaci
Bemisia tabacie0pest - Outcome
- Differencese0
- Qualifier
- CBSD inoculum pressuree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Differences were driven by Bemisia tabaci whitefly vector abundance and CBSD inoculum pressure.”
t0“cassava”
Claim · model-written summary
CBSV and UCBSV were nearly equally represented around plots, with differing regional predominance.
- Taxon
- cassavaManihot esculentae0
- Outcome
- CBSV and UCBSVe0
- Setting
- cassava fields surrounding experimental plotse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both CBSV and UCBSV were almost equally represented in cassava fields surrounding experimental plots, although CBSV predominated in the north-west whilst UCBSV was more frequent in coastal and southern sites.”
Claim · model-written summary
CBSV incidence exceeded UCBSV incidence in initially virus-free plots.
- Taxon
- cassavaManihot esculentat0
- Interactor
- CBSVe0pathogen
- Outcome
- incidence of CBSVe0
- Direction
- much greatere0
- Comparator
- UCBSVe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the incidence of CBSV was much greater than that of UCBSV in initially virus-free experimental plots”
t0“cassava”
Claim · model-written summary
Cultivars formed three groups by shoot and root CBSD symptoms.
- Taxon
- cassavaManihot esculentat0
- Outcome
- three groupse0
- Value
- three groupse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cultivars could be categorised into three groups based on the degree of CBSD symptom expression in shoots and roots.”
t0“cassava”
Claim · model-written summary
Seven resistant cultivars each had shoot and root incidence below 20%.
- Taxon
- cassavaManihot esculentat0
- Material
- F10_30R2, Eyope, Mkumba, Mkuranga1, Narocass1, Nase3 and Orerae0
- Outcome
- shoot and root incidencese0
- Value
- less than 20%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The seven cultivars (F10_30R2, Eyope, Mkumba, Mkuranga1, Narocass1, Nase3 and Orera) in the most resistant category each had shoot and root incidences of less than 20%.”
t0“cassava”
Claim · model-written summary
Fresh root yield differed among sites and cultivars.
- Taxon
- cassavaManihot esculentat0
- Outcome
- Fresh root yielde0
- Direction
- differede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fresh root yield differed between sites and cultivars”
t0“cassava”
Claim · model-written summary
Root yield showed no genotype by environment interaction.
- Taxon
- cassavaManihot esculentat0
- Outcome
- genotype by environment interactione0
- Setting
- environmente0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no genotype by environment interaction for this trait”
t0“cassava”
Claim · model-written summary
Susceptible cultivars and local check performed well without CBSD pressure.
- Taxon
- cassavaManihot esculentat0
- Outcome
- performed welle0
- Qualifier
- absence of CBSD pressuree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Susceptible cultivars and the local check performed well in the absence of CBSD pressure”
t0“cassava”
Claim · model-written summary
The authors recommend improved and local germplasm plus phytosanitary measures for CBSD management.
- Taxon
- cassavaManihot esculentat0
- Outcome
- combine the deployment of improved cultivars with phytosanitary control measurese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This should use both improved and local germplasm resources to generate high yielding cultivars for specific end-user traits, and combine the deployment of improved cultivars with phytosanitary control measures including the use of healthy planting material and planting during periods of reduced CBSD infection.”
t0“cassava”