Browsing by Author "Isutsa, D. K.1"

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Current characteristics of cassava mosaic disease in post-epidemic’ areas increase the range of possible management options.
(Association of Applied Biologists, 2006-06-05) Mallowa, S. O.1; Isutsa, D. K.1; Kamau, A. W.1; Obonyo, R.2; Legg, J.P 2,3; ; ;
As a case study to document the current characteristics of cassava mosaic virus disease (CMD) in postepidemic areas, surveys were carried out, in 2003 and 2004, in Siaya District of western Kenya. This was an area affected by a severe CMD pandemic in the late 1990s. Data recorded on cassava varieties were CMD incidence, severity index and number of adult whiteflies. Farmers (174) were interviewed on their understanding of the disease and their knowledge and practice of management interventions. Cassava cultivation was being reestablished, but local landraces predominated. Resistant varieties were present 13% in 2003, and 4% in 2004, of the surveyed fields. Adhiambolera was the most common variety, occurring in 35% and 40% of fields in 2003 and 2004, respectively, and had an average CMD incidence of 82% in 2003 and 73% in 2004. By contrast, the CMD-resistant variety Migyera had a low mean incidence (28% in 2003). The overall incidence for both years was 71%, consisting of 61% as a result of infection through planting diseased cuttings and 10% as a result of whitefly infection. In 2003, the total incidence was 72% and the average severity 2.7 (severity index), while in 2004 the incidence was 78% and the severity 2.6. There were significant severity variations in each division of the Siaya District during the 2 years except for Karemo and Ukwala. The abundance of whiteflies on the top five leaves of plants was low in 2003 but high in 2004, with means of 1 and 16, respectively, over the same seven divisions in both years, although this variation was thought to be because of seasonal factors. East African cassava mosaic virus-Uganda was the predominant geminivirus present in every division. Phytosanitation by farmers was minimal, as evidenced by 29% of farmers using a selection of CMD-free stems for planting and 15% using hand-roguing for CMD management. Occurrence of more than 25% CMD-free plants in 2004, moderate CMD severity and limited spread provide a conducive environment for the use of phytosanitation as a CMD control measure that can be immediately used by farmers growing their own cassava varieties.
Effectiveness of phytosanitation in cassava mosaic disease management in a post-epidemic area of western Kenya
(2011-07) Mallowa, S. O. 1; Isutsa, D. K.1; Kamau, A. W.1; Legg, J. P.2; ; ;
The effectiveness of phytosanitation in managing cassava mosaic disease (CMD) was studied in a post-epidemic area of western Kenya. Four varieties [MM96/4466 (resistant), TMS 30572 (Migyera, moderately resistant), Bukalasa 11 (Serere, moderately susceptible) and Karemo (susceptible)] and four phytosanitation approaches (roguing, cutting selection, roguing plus cutting selection, and none) were studied at two sites (Alego and Ugunja) for two seasons. With no phytosanitation, resistant varieties had very low levels of CMD infection, and infected plants expressed very mild symptoms. By contrast, the most susceptible variety became heavily diseased, with incidences of > 90%, whether phytosanitation measures were applied or not. Tuberous root yields were highest for CMD-resistant varieties. Roguing susceptible varieties resulted in significantly reduced root yields compared to the 'do nothing' control, largely as a result of the greatly reduced plant population. However, plots of CMD-susceptible varieties where selection was applied gave tuberous root yields that exceeded those of the control and that were comparable to those of the resistant variety with the equivalent treatment. These data clearly demonstrate the value of selection as an approach for maintaining the production of local varieties under the CMD post-epidemic conditions that are now prevalent across large areas of East and Central Africa. Conversely, the results show that roguing provides no tuberous root yield benefit under any of the tested circumstances. Raising awareness amongst farming communities of the potential advantages of selection of healthy planting material should be an important component of CMD management programmes, in tandem with efforts to multiply and disseminate planting materials of resistant varieties.