Effects of Sweet Potato Feathery Mottle Virus and Sweet Potato Chlorotic Stunt Virus on the Yield of SweetPotato in Uganda

Abstract

Sweet potato feathery mottle virus (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV) are the most common viruses infecting sweetpotato in Uganda. Field plots planted with graft inoculated plants of virus-free cultivars Beauregard, Dimbuka, Ejumula, Kabode and NASPOT 1 were used to assess the effect of SPFMV and SPCSV on yield and quality of sweetpotatoes in two agro-ecologies. SPFMV spreads rapidly to control plots at Makerere University Agricultural Research Institute Kabanyolo (MUARIK), and these plots had similar yields to those singly infected with SPFMV but at the National Semi Arid Resource Research Institute (NaSARRI) where SPFMV spreads slowly, plots infected with SPFMV yielded 40% less than the control. Recovery from SPFMV appeared to be more frequent at NaSARRI than at MUARIK. Infection by SPCSV alone resulted in yield losses of 14-52%, while mixed infections of SPFMV+SPCSV resulted in yield losses in both locations of 60-95% depending on the cultivar. SPCSV and mixed infections of SPFMV+SPCSV also reduced the number of roots formed as well as the diameter of the roots, resulting in a greater length to diameter ratio compared to the healthy control. This study, therefore, confirms that both SPFMV and SPCSV, both singly and when mixed, can reduce yield, the extent depending on the cultivar. To mitigate the effect of these viruses, farmers should use clean planting materials of resistant varieties.

Effect of temperature on sweet potato virus disease symptom expression

“…This is in agreement with the earlier observations by Wasswa (2010), Adikini et al (2016) and Gibson et al (2014) though most of these authors did not vary temperatures to wide ranges. Sweet potato infected with SPVD and grown under glasshouse conditions produce little or no tuber yield, and this observation concurs with that of Adikini et al (2016). SPVD presence also influenced the number of leaves.…”

“…Previous studies reported that some areas such as central Uganda had higher SPVD incidences and severities than for instance the eastern region (Adikini et al, 2016). The two regions differ in average ambient temperature, among other climatic aspects; with the eastern being hotter than the central region.…”

“…SPVD is the most important disease of the crop that threatens sweet potato in the tropics (Kpaka et al, 2013). It causes yield losses of up to 95%; there are no reports of immune cultivars (Adikini et al, 2016;Gibson et al, 2014;Sanginga and Mbabu, 2015). However, there exist good levels of SPVD resistance among the commonly grown sweet potato varieties in high infection areas (Kpaka et al, 2013).…”

“…In addition, the incidence and severity of pathogens is strongly influenced by the interaction of temperature, vectors, hosts, and pathogen genetics (Adikini et al, 2016;Mwanga et al, 2016). From one environment to another, climatic aspects namely rainfall patterns and intensity, relative humidity, wind speed and direction, and temperature tend to differ and fluctuate none equivocally Sabaghnia et al, 2012).…”

“…The two regions differ in average ambient temperature, among other climatic aspects; with the eastern being hotter than the central region. It has been suggested that high temperature favours recovery from SPVD (Adikini et al, 2016;Gibson et al, 2014). There are increasing reports on rise of SPVD outbreaks in traditionally disease free agro-ecologies in Uganda.…”