First Report of Sweetpotato symptomless virus 1 and Sweetpotato virus A in Sweetpotatoes in Tanzania
Authors: Mbanzibwa D. R. , Tairo F. , Gwandu C. , Kullaya A. , Valkonen J. P. T. 
Published: November 2010

Sweetpotato (Ipomea batatas L.) is grown widely from tropical to temperate regions and is an important food security crop in tropical countries. In Africa, sweetpotato is infected by RNA viruses of many taxa (4), but DNA viruses, such as the genus Begomovirus (family Geminiviridae), infecting sweetpotatoes in the Americas have been reported only in Kenya (3). A caulimo-like DNA virus (family Caulimoviridae) has been detected in sweetpotatoes in Uganda (1). Recently, two novel badnaviruses (genus Badnavirus, family Caulimoviridae) and a new mastrevirus (genus Mastrevirus, family Geminiviridae) were discovered in a local sweetpotato cultivar maintained in a germplasm collection in Peru (2) but were not reported elsewhere. This study examined the possible existence of these novel viruses in landrace sweetpotato varieties grown in Tanzania. Nine landrace sweetpotato varieties and one introduced cultivar (NIS 91 from the International Potato Centre, Peru) were sampled from six regions of Tanzania. DNA was extracted (2) and amplified by PCR using primers (MastvKF: 5′-GACAGACCCCTAGGGTGA-3′; MastvsR 5′-ACTGCATATAGTACATGCCACA-3′) designed in this study to amplify partial, putative movement and coat protein gene sequences of Sweetpotato symptomless virus 1 (SPSMV-1) (GenBank Accession No. FJ560945) (2). Products of the expected size were detected in seven samples (varieties Ex-London, Ex-Lyawaya, Gairo, Hombolo, Kagole white, Mbeya, and Shangazi) representing four regions surveyed (Dodoma, Mbeya, Morogoro, and Kagera). PCR products from five samples were sequenced (396 nt; GenBank Accession Nos. HQ316938 to HQ316942) and found to be identical to each other and the isolate described originally in Peru (2). Amplification with primers (BadnaBKF: 5′-CAAATTAGGAGGCAGATAAATG-3′; BadnaBsR: 5′-GGTCTTCTTATGTTCCACCTT-3′) designed in this study according to the sequence of Sweetpotato virus B (SPBV-B) (GenBank Accession No.FJ560944) resulted in products of the expected size in three samples (varieties Ex-Lyawaya, Gairo, and Hombolo collected in Mbeya, Morogoro, and Dodoma, respectively) that were positive also for SPSMV-1. Sequences of the products (787 nt; HQ316935 to HQ316937) were nearly identical (99.4%). They were 96.8 to 96.9% similar to a region (nts 830-1616) of Sweetpotato virus A (SPBV-A; FJ560943) (2), whereas they were only 83.2 to 83.6 % similar to the corresponding region (1,486 to 2,272 nt) of SPBV-B (FJ560944) (2). No virus was detected in cv. NIS 91. All plants sampled exhibited mild mottling or mosaic symptoms, but a contribution to the symptoms by other untested viruses cannot be excluded because few of the large number of sweetpotato viruses have been studied in Africa (4). To our knowledge, this is the first report of SPSMV-1 and SPBV-A outside South America and in sweetpotatoes grown in the field. The results show that the two viruses are distributed widely in local sweetpotato varieties in Tanzania, which suggests that they may be found in other sweetpotato-growing areas where they have not been studied. While the yield losses caused by SPSMV-1 and SPBV-A remains to be studied, the data from this study are of practical importance in terms of regional and international exchange of sweetpotato germplasm.

References: (1) V. Aritua et al. Plant Pathol. 56:324, 2007. (2) J. F. Kreuze et al. Virology 388:1, 2009. (3) T. Paprotka et al. Virus Res. 149:224, 2010. (4) F. Tairo et al. Mol. Plant Pathol. 6:199, 2005.