Evaluation of exotic and locally adapted sweetpotato cultivars to major viruses in Ethiopia

Sweetpotato virus disease (SPVD) is currently threatening sweetpotato production in Ethiopia than ever, with more viruses unidentified earlier being detected in more recent years. Due to the increased importance of virus diseases, management option using host plant resistance was planned using local cultivars and exotic genotypes for three consecutive years (2011-2013) at Hawassa, Ethiopia. A total of 89 sweetpotato introductions from international sources, and clones of 26 locally adapted cultivars were used for this study. The materials were evaluated at three stages of screening under natural infection, where Hawassa is selected as hotspot area for sweetpotato viruses based on observations made in the previous years. Genotypes were planted in a single row observation plot in preliminary screening, and randomized complete block design (RCBD) in advanced screening. Symptomatology was used to evaluate the reaction of genotypes in the field and supplemented by three times serological testing (NCM-ELISA) during each experiment using a battery of 10 antibodies against the common viruses known to infect sweet potato. The results of laboratory analysis have ascertained the occurrence of six new viruses not reported to exist in Ethiopia before, viz. C-6 virus, Sweetpotato caulimo-like virus (SPCaLV), Sweetpotato chlorotic flecks virus (SPCFV), Sweetpotato mild speckling virus (SPMSV), Cucumber Mosaic Virus (CMV) and Sweetpotato latent virus (SwPLV). All of the newly identified viruses were detected on exotic sweet potatoes obtained from international sources, suggesting the possibility of their introductions along with the planting materials and hence the need of establishing strong quarantine inspection. Among 25 genotypes evaluated in advanced screening, 14 genotypes (13 from exotic sources and one local) were apparently virus free. These materials need be tested at multi-locations for further use in improvement programs. Highly significant difference (p< 0.01) was observed for virus disease severity and storage root yield among sweetpotato genotypes indicating the possibility of selection for resistant /tolerant/ clones against sweetpotato virus disease (SPVD). Use of vines from infected fields of sweetpotato resulted in the decline in yield and stand establishment across years. Within virus susceptible genotypes, 47.8% – 92.6% yield reduction was witnessed in the third year of the experimental period. Similarly out of planting materials used from infected plots, 75-85 % of the vines showed poor establishment when compared to vines taken from virus free plots. This signifies the importance of periodically renewing planting materials from virus free sources