Yield evaluation of multiple and co-infections of begomoviruses and potyviruses on sweet potato varieties under field conditions and confirmation of multiple infection by NGS

Abstract

Potyviruses and begomoviruses are regarded as the most common viruses affecting sweet potato production in South Africa (SA). The impact of single and mixed virus infections on the yield of sweet potato varieties have not been established in SA. The objective of this study was to determine the effects of potyviruses and begomoviruses on sweet potato total and marketable yield. Twelve varieties, 8 locally bred and four imported, were selected for evaluations and these were graft-infected with different virus combinations: 1) co-infections of the russet crack (RC) strain of Sweet potato feathery mottle virus (SPFMV) + Sweet potato virus G (SPVG) + Sweet potato virus C (SPVC) + begomoviruses [Sweet potato leaf curl Sao Paulo virus (SPLCSPV) + Sweet potato mosaic virus (SPMV)] [(treatment (T) 1)]; 2) co-infections of SPFMV (RC strain) + begomoviruses (T2); 3) single infection of the RC strain of SPFMV (T3); and 4) co-infection of the begomoviruses SPLCSPV and SPMV (T4). Next generation sequencing (NGS), reverse transcription polymerase chain reaction (RT-PCR) or PCR confirmed the identification of the viruses in sweet potato plants used as sources of various treatments. Two consecutive field trials were planted in January 2014 and 2015, respectively. Varieties produced significantly reduced total [(F11, 236 = 5.17); P < 0.0001)] and marketable [(F11, 236 = 3.65); P < 0.0001)] yield with all the treatments in both the trials. Treatment 1 reduced the total yield by between 66% and 93% in trial 1, and by 66% and 99.5% in trial 2. The loss in marketable yield ranged between 67% and 98% in trial 1, and 58% and 100% in trial 2 with T1. Treatment 2 also led to reduced average total yield of varieties by between 28% and 94% in trial 1 and the total yield was severely reduced by between 74% and 99% in trial 2. Similar trends were recorded for the marketable yield of varieties treated with T2. The total yield reduced with T3 was between 27% and 78% in trial 1 and varieties such as Bophelo, Hernandez, Impilo and Ribbok had yield reduction of less than 50% when compared to the other eight varieties, however, total yield was severly reduced in trial 2 (61%–99%) for all varieties. Similar trends were also observed with marketable yield of varieties treated with T3. Total yield was also reduced with begomovirus co-infections (T4) and yield loss was between 32% and 84% in trial 1 and varieties such as Bophelo, Bosbok, Mvuvhelo, Ndou and Resisto had yield reduction of less than 50% when compared to the other seven varieties. Total yield was severely reduced in trial 2 with T4 and only varieties 199062.1 and Hernandez had yield reduction of less than 50%. Marketable yield was also reduced with T4 and only varieties Bophelo, Bosbok, Mvuvhelo and Ndou had yield reduction of less than 50% in trial 1. The results demonstrate that single or co-infections of potyviruses and begomoviruses have variable negative effects on the yield of sweet potato varieties.