Response of sweetpotato germplasm to sweetpotato virus disease and molecular characterization of sweetpotato mild mottle virus

Abstract

Sweetpotato virus disease (SPVD) is the most economically important disease affecting sweetpotato production in Kenya, causing yield reduction of up to 90%. Sweetpotato mild mottle virus (SPMMV) also increases the severity of symptoms expressed in SPVD-infected plants. To address this challenge, twenty sweetpotato genotypes were evaluated for it in this study. Two field trials were set up in Kenya Agricultural and Livestock Research Organization (KALRO) Kakamega and Yala swamp. The genotypes were planted in 5m x 3m plots in rows spaced at 100 cm and intra row spacing of 30cm. the experiments were laid out in a randomized complete block design (RCBD) with three replications. Disease severity was scored every month for a period of five months by visually assessing the severity of symptoms on a scale of 1 to 5. To determine genetic variability of SPMMV, PCR products were sequenced and compared with sequences of 14 East African SPMMV isolates from the National Center for Biotechnology Information (NCBI) gene bank using the DNAMAN version 4.02 software. To determine the vector for SPMMV, white flies (Bemisia tabaci) were allowed six access acquisition periods (AAP) of 0, 6, 12, 24, 48 and 72 hours of feeding and a uniform inoculation access period (IAP) of 48 hours. After six weeks, leaves from the inoculated I. setosa plants were evaluated for presence of SPMMV using an Enzyme Linked Immunosorbent Assay on Nitro cellulose membranes (NCM-ELISA). The virus transmission was calculated by expressing the number of infected recipient I. setosa plants as a percentage of the total number of recipient plants used. The test sweetpotato genotypes exhibited significant differences (P<0.05) in disease severity. The results indicated that four genotypes, KKFS 56682-03-1, Marooko-3, YS Sopalla and YS Kemb 10 were tolerant to SPVD. Nucleotide sequence similarity of the SPMMV isolates sequenced ranged between 71% and 97% indicating a high genetic variability among the SPMMV isolates. Transmission of SPMMV was observed at the 48 and 72 hours AAP.