Cassava brown streak disease is endemic to the coastal regions of East Africa and from around 2004 the disease resurged and became epidemic in the Great Lakes Region, where it continues to spread. In both these areas CBSD leaf symptoms occur at high incidences.However, it is the associated symptom of root rot (necrosis) in the starch-bearing tissues that renders the root unfit for human consumption. Because the extent of root necrosis is not known until the crop is harvested and surveys require destructive sampling, root symptoms are much less frequently assessed than are the above-ground symptoms on the leaves and stems. Surveys were undertaken in selected villages in Tanzania, Kenya, Uganda and Malawi to assess the incidence of CBSD leaf symptoms and the incidence and severity of root symptoms, in order to estimate the impact of the disease on household food security and on cassava processing. CBSD leaf symptoms were recorded at high incidences [40 -90% in individual fields] in all fields visited throughout East Africa but root necrosis incidence was lower than would be expected from the high incidence of leaf symptoms. Severe root necrosis at high incidence was found only on a few varieties, usually grown to a limited extent. It appears that varieties that are prone to root necrosis are being abandoned in favour of those with a lower propensity to develop root necrosis after infection by the virus.
Objective: Senna didymobotrya (African senna, African wild sensitive plant, peanut butter cassia, peanut butter tree, popcorn cassia, popcorn senna or wild senna) is native to East Africa and is widely used as a medicinal plant among many communities in Kenya. The objective of this research was to evaluate the presence of phytochemicals present in the different plant parts and their antibacterial activity. Methodology and results: Leaves, flowers, stem bark, immature pods and root barks were collected from Siaya, Nandi and Nakuru Counties. These were dried and ground. Methanolic crude extracts were in cooperated in nutrient media at 2.5 %, 5 %, 7.5 % and 10 %. Test organisms Staphylococcus aureus and Escherichia coli were inoculated on impregnated media, incubated and observed for colony development. Observation on growth of cultures was made at an interval of 2 days for 8 days. The area under disease progress stairs (AUDPS) was calculated using the derived colony surface areas. Results indicated that all plant parts contained terpenoids, phenols and steroids. The presence of alkaloids and flavonoids varied with the location the plant was collected and the plant part. Growth of S. aureus cultures grown on media impregnated with 2.5% root bark extract and that with 7.5% stem bark extract were completely inhibited (no growth). Media with 10% flower, pods and leaves extract had average reduction of colony sizes from AUDPS 10102 (control) to AUDPS 2475. Growth of E. coli was completely inhibited on media impregnated with 5% root bark extract and 7.5% stem bark extracts. At 10% concentration, the flowers, pods and leaves extract did not result in complete inhibition of colony growth. Conclusions and applications: The present research suggests that S. didymobotrya extracts possessed antibacterial activity against bacterial pathogens thus supporting their folkloric usage, promising a future scope for its use against microbial populations. Methanolic extracts possessing high antibacterial effects should be further investigated for their therapeutic utility. This would be related to the presence of bioactive metabolites, which are soluble in methanol. There is need to explore further the quantities of phytochemicals in the root and
11358stem barks that make them more potent than the other plant parts. The structures of the bioactive metabolites should be examined in future.
A farm survey was conducted in Kuria East and Suna West sub-counties to determine the incidence, severity and estimated losses of cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) on cassava crops in farmers' fields. The results showed that cassava is the second most important staple crop after maize in Migori County. CMD incidence ranged from 0.0 to 56.7%) in Kuria East and 10.0 to 55.0% in Suna West. CBSD incidences were much higher at 5.0 to 74.0% in Kuria East and 10.0 to 77.5% in Suna West. Both CMD and CBSD had an effect on yield reduction and total root loss ranged from 10.7 to 47.2% in Kuria East and 11.5 to 33.2 in Suna West. The percent mean total root loss in Kuria East was 25.9%; equivalent to 1299.6 US dollars/ha while in Suna East was 24.7%; equivalent to 1259.5 US dollars/ha. The best performing variety with regards to low CBSD and CMD incidence, low root losses and high yield were TMS 30572 and MH95/0183. The findings of this study are expected to provide impetus for the development and promotion of new high yielding, locally adapted and resistant cassava varieties.
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