Characterising reversion from virus infection in sweetpotato

Abstract

Sweetpotato (Ipomoea batatas) production is negatively impacted by viral infections. However, some East African sweetpotato cultivars were recently reported to “fight off” viral infection through reversion process. Very few reverting cultivars have been reported and as a a resistance mechanism, it has been postulated to be associated with genetic nature of the plant. Secondly, it is speculated that some environmental conditions could favour reversion. This study aimed at understanding reversion as one of the means to viral disease management using East African cultivars New Kawogo, NASPOT 1 and NASPOT 11, and the USA cultivars Resisto and Beauregard. This was done through evaluating the potential of different sweetpotato cultivars to revert from various virus infections. Reversion potential was also tested under different temperature regimes and soil amendments. In silico methods were used to evaluate the genes associated with reversion, and their segregation pattern. Also heritability of reversion from virus infection of sweetpotato progeny was tested. The study revealed that sweetpotato plants, especially the East African cultivars, reverted from single infections of Sweet potato feathery mottle virus, Sweet potato virus C, Sweet potato mild mottle virus and Sweet potato leaf-curl - Uganda virus. None of the tested cultivars fully reverted from single or double infections involving Sweet potato chlorotic stunt virus. Reversion generally increased with increasing temperature and improved soil nutrition. Further, the study predicted reversion to be due to defense genes including; RNA dependent RNA polymerases 1, 2, 5, and 6; Argonaute 1; and Dicer-like 1, 2, and 4. These genes were phylogenetically related to similar genes in other crops. Variants of several of these genes were observed on different chromosomes. These defense genes contained mono-, di-, tri-, tetra-, penta-, and hexa-nucleotide repeat motifs, and the SSR markers within progenies of sweetpotato crosses - segregated in disomic, co-segregation, nullisomic, monosomic, and trisomic modes. Reversion potential varied among the progeny for which broad and narrow sense heritability were 76.42% and 42.4%, respectively. These results indicated that reversion was a heritable trait determined by multiple genes. This study therefore shows that reversion is influenced by the type of virus infecting sweetpotato, soil nutrition enhancement and temperature. By utilising conditions observed in this study (in consonance with appropriate agronomic practices), could further enhance control, management and mitigating the spread of viral infections in sweetpotato, thus secondarily contributing to food security.