Cultivar decline in sweetpotato: II. Impact of virus infection on yield and storage root quality in 'Beauregard' and 'Hernandez'

To determine the effects of Sweet potato feathery mottle virus (SPFMV), and possibly other newly described potyviruses, on sweetpotato yield and storage root appearance, virus-indexed 'Beauregrd' and 'Hernandez' mericlones testing free of known viruses were compared with virus-infected mericlones in two separate experiments over two years. The experiments were arranged in a split-plot,randomized, complete-block design with the initial presence (VI+) or absence (VI-) of SPFMV as the whole plot factor and mericlone as the subplot factor. Plants were monitored weekly for symptoms of SPFM and vine samples were taken for virus-indexing on Ipomoea setosa. Additional testing for selected sweetpotato viruses was done using a nitrocellulose membrane enzyme-linked immunosorbant assay. SPFMV was the only virus detected in the study, using available testing methodologies. Field monitoring indicated that approximate to100% of the VI- plants were reinfected with SPFMV by 9 weeks after planting. The presence of virus before planting reduced yields of No. 1 roots by 26% and decreased overall appearance ratings for the three 'Beauregard' mericlones. In addition, VI+ planting Materials resulted in increased storage root length and reduced storage root width of both cultivars leading to increased storage root length/diameter ratios, further detracting from overall storage root appearance. The results of this study demonstrate that SPFMV contributes to cultivar decline in sweetpotato. However, the interaction of SPFMV with other newly described potyviruses, which may result in synergistic negative effect. S on sweetpotato yield and quality, needs further research.