Abstract
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. Key words: Temperature, disease symptom expression, viruses, Ipomea batatas, growth response.
Highlights
Sweet potato (Ipomoea batatas, family Convolvulaceae) is of great importance to Uganda and other African countries such as Rwanda and Burundi because of its various food and feed uses (Kpaka et al, 2013)
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 sweetpotato virus disease (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
For New Kawogo, it was observed that symptom development did not change systematically with plant age unlike the rest of the cultivars where severity scores generally increased with plant age, with Tanzania showing the clearest forward trend (Table 2)
Summary
Sweet potato (Ipomoea batatas, family Convolvulaceae) is of great importance to Uganda and other African countries such as Rwanda and Burundi because of its various food and feed uses (Kpaka et al, 2013). According Kpaka et al (2013), Uganda is the biggest producer of sweet potato in Africa but its low average yield of 4.58 t/ha (compared to experimental yield estimates of 25 t/ha) makes it impossible to satisfy the country’s production demand. Major constraints such as pests and diseases explain the crop’s current low yields (Kpaka et al, 2013; Sanginga and Mbabu, 2015). This study was focused on gaining an insight into the effect of temperature on the development of SPVD and growth of sweet potato
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