Prevalence and implications of sweetpotato recovery from sweet potato virus disease in Uganda

Abstract

Sweet potato virus disease (SPVD) is the most important disease of sweetpotato in the tropics. It causes yield losses of up to 98% and extinction of elite cultivars. Although there are no reports of immune cultivars, disease recovery phenomenon (a manifestation of some form of resistance) was reported in many vegetatively propagated crops including sweetpotato. A total of 1320 sweetpotato cultivars from 3 major sweetpotato growing regions in Uganda were field evaluated for SPVD severity, of which 24% showed recovery from SPVD. The nature of SPVD recovery was assessed in the screenhouse using 20 distinct cultivars after graft inoculation with SPCSV and SPFMV, the SPVD causing viruses. SPVD progress in 20 graft inoculated cultivars was significantly (P<0.05) different; Munyeera was the most resistant cultivar followed by New Kawogo and Polyster. The 3 resistant cultivars (disease score 1-2) displayed recovery from SPVD which was correlated with a reduction in SPFMV titers as observed from quantitative ELISA. Reversion was not evident since all cuttings taken from recovered vine tips later tested positive for both viruses. Cultivars with the ability to recover were common in farmers’ fields in central (36.4%) and western (33.3%) regions of Uganda, which are high SPVD pressure zones. Conversely, fewer cultivars (5.6%) from the low disease pressure eastern region displayed recovery. The very susceptible cultivars (disease score of 4-5) were not prevalent in central and western regions. These observations suggest that SPVD recovery has an influence on the cultivars grown in different SPVD pressure zones, where more susceptible cultivars are preferred in areas of low disease pressure.