Browsing by Author "Kyamanywa Samuel"

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Effect of temperature on sweet potato virus disease symptom expression
(Uganda Martyrs University, 2019) Sseremba Godfrey; Mukasa Settumba; Kyamanywa Samuel
The incidence and severity of sweetpotato virus disease (SPVD) was reported to be highly variable under different agroecological zones in Uganda, a situation that could be partly attributable to differences in temperature. This raised a need for understanding the effect of temperature on the biology of SPVD causative agents which ultimately influences disease development and symptom expression that undermines productivity among sweet potato cultivars. This study was carried out at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK). Initially clean sweet potato cultivars were inoculated with two viruses namely Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato feathery mottle virus (SPFMV) that cause SPVD when co-infecting sweet potato and established at two temperature environments; field and glasshouse, followed by a weekly interval monitoring of the plants for symptom expression and growth response. Temperature differences significantly (p<0.001) influenced SPVD severity and the growth response of different sweet potato cultivars. Overall, the plants under field conditions where temperature was lower produced higher SPVD severity than under glasshouse where higher temperatures were recorded. SPVD severity for most of the cultivars was higher in the field than under glasshouse. Cultivar (cv.) Ejumula displayed the highest severity levels followed by cvs. Tanzania and Beauregard. Conversely, New Kawogo, Dimbuka and Naspot 1 showed none to mild severities particularly under the glasshouse conditions. Therefore temperature influenced the development of SPVD; low temperatures of 20 to 29°C produced more disease severities than high temperatures of 30 to 39oC. It is suggested that reasonably high temperatures under a controlled environment should be incorporated in any sweet potato seed production system for possible elimination of SPVD.
Interaction of the predatory ant Pheidole megacephala (Hymenoptera: Formicidae) with the polyphagus pest Xylosandrus compactus (Coleoptera: Curculionidea)
(Elsevier Science, 2017) Ogogol Rajab; Egonyu James P.; Kyamanywa Samuel ; Erbaugh Mark; Bwogi Godfrey
We evaluated the potential of using Pheidole megacephala as a biological control agent against the coffee twig borer Xylosandrus compactus (Eichhoff), an economically important pest of Robusta coffee in Uganda. Upon observing that P. megacephala was common in coffee fields infested by X. compactus, we tested hypotheses that (1) P. megacephala feeds on all stages of X. compactus, (2) P. megacephala can enter galleries of X. compactus inside coffee twigs in search for the prey and (3) P. megacephala’s presence on infested twigs reduces populations of X. compactus in the galleries. In a Petri dish bioassay over 24 h, we found that P. megacephala preyed upon all stages of X. compactus without indication of preference. We caged up X. compactus infested twigs with P. megacephala in a plastic container over 48 h and found that the predator was unable to enter the galleries. Lastly, we caged up intact X. compactus infested coffee twigs in the field with muslin cloth sleeves for one month and found that P. megacephala reduced the population of X. compactus per twig by almost 22-fold compared to the untreated control. We concluded that P. megacephala is an indiscriminate predator of all X. compactus stages, and, though unable to enter X. compactus galleries, the predator may reduce X. compactus population on infested twigs. Exploitation of P. megacephala in the biological control of X. compactus on coffee and other crops would require additional studies on how to enhance presence of the predator on the infested crop.
Relationship between Tomato Yellow Leaf Curl Viruses and the Whitefly Vector
(African Journals Online, 2010) Ssekyewa C.; Van Damme P.; Nagawa F.; Kyamanywa Samuel; Steele K. A.
Tomato yellow leaf curl is prevalent in tomato growing districts of Uganda. The disease is known to be spread by a whitefly (Bemisia tabaci) in a persistent manner. Some of its symptoms are leaf curl, marginal leaf yellowing, malformation of fruits, stunting and dieback (in case of primary infection at early seedling stage), so the disease is economically important. Therefore, this study delved into the relationship between the disease and the vector in selected agro-ecosystems in the Country. The influence of weather and seasonality on the incidence of the disease and the vector was also investigated through a series of field experiments across a period of two years. New methods for trapping the vector were developed and applied to estimate its populations on individual plants and in the overall field environment. The findings were that whereas incidence of the disease is low at seedling stage, the whitefly population is highest at this stage. It was also found that the vector population is favoured by drought, so rainy conditions reduced it tremendously.