Sweetpotato Virus C and Its Contribution to the Potyvirus Complex in Sweetpotato (Ipomoea batatas)

In Louisiana, sweetpotato (Ipomoea batatas) is infected in Louisiana by the four ubiquitous potyviruses: Sweetpotato feathery mottle virus (SPFMV), Sweetpotato virus G (SPVG), Sweetpotato virus 2 (SPV2) and the strain of SPFMV previously known as the common strain, recently renamed as Sweetpotato virus C (SPVC). These four viruses belong to the Potyviridae family, with single stranded RNA of ~11kb. In this group of plant viruses, a single polyprotein is coded entirely but later cleaved into ten mature proteins: P1, HC-pro, P3, 6K1, CI, 6K2, NIa-VPg, NIa-Pro Nib and Coat Protein (CP). In sweetpotato potyviruses, two additional open reading frames produced by polymerase slippage called PIPO and PISPO act as RNA silencing suppressors. Despite the minimal differences at the nucleotide level in these four viruses, their titers, vector transmissibility and presence in the field are different. The objectives of this research were: (i) redesign the qPCR assay of SPFMV and SPVC and determine the best organ and sampling time after sweetpotato transplanting to detect each of these four viruses; (ii) determine if SPVC is the missing element in reproducing the observed yield reduction of natural infections that occur in the field and; (iii) determine the complete sequences of nine isolates from sweetpotato production fields in Louisiana and analyze the genetic structure and variability compared to other isolates present in the world. Results suggested that leaf tissue at the 3rd week after transplanting is the best organ to sample to determine if the plant is infected with the four potyviruses. The inclusion of SPVC did not reproduce the storage root reduction observed under naturally infected plants and, the molecular variation was not high from other isolates previously sequenced but six isolates report recombination events in the CP and P1 region of their genome