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D.W. Miano, D. R. LaBonte and C. A. Clark

Sweetpotato is an important staple food crop in Sub-Saharan Africa, with production being concentrated in East Africa, particularly around Lake Victoria. Productivity of the crop is greatly constrained by viral diseases. Four main viruses have consistently been detected from various surveys done in the region viz. sweet potato feathery mottle virus (SPFMV), sweet potato chlorotic stunt virus (SPCSV), sweet potato mild mottle virus (SPMMV), and sweet potato chlorotic fleck virus (SPCFV). Sweet potato caulimo-like virus (SPCaLV), sweet potato latent virus (SPLV), and cucumber mosaic virus (CMV) have also been detected though only in isolated cases. The most severe symptoms have been caused by co-infection with SPCSV and SPFMV, resulting in the synergistic Sweet potato virus disease (SPVD). Yield reductions due to virus infections have been estimated to be >90% in very severe cases. Virus detection has mainly been limited to the use of serological methods. Some plants have been observed with symptoms resembling those caused by viruses, but do not react with available antisera, indicating that the plants could be infected with viruses that have not been described, or not tested in the region. Use of other detection techniques such as PCR may result in identification of more viruses in the region. This report gives a summary of our research efforts towards detection of other viruses present in the region, and identification of resistant germplasm.

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Robert O.M. Mwanga, Charles Niringiye, Agnes Alajo, Benjamin Kigozi, Joweria Namukula, Isaac Mpembe, Silver Tumwegamire, Richard W. Gibson and G. Craig Yencho

good to excellent consumer acceptance, depending on growth conditions. The cultivar has moderate to high field resistance to sweetpotato virus disease (SPVD) and Alternaria bataticola blight. Both diseases can be devastating, causing high storage root

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R.O.M. Mwanga, A. Kriegner, J.C. Cervantes-Flores, D.P. Zhang, J.W. Moyer and G.C. Yencho

When sweetpotato chlorotic stunt crinivirus (SPCSV) and sweetpotato feathery mottle potyvirus (SPFMV) infect sweetpotato [Ipomoea batatas (L.) Lam.], they interact synergistically and cause sweetpotato virus disease (SPVD), a major constraint to food productivity in east Africa. The genetic basis of resistance to these diseases was investigated in 15 sweetpotato diallel families (1352 genotypes) in Uganda, and in two families of the same diallel at the International Potato Center (CIP), Lima, Peru. Graft inoculation with SPCSV and SPFMV resulted in severe SPVD symptoms in all the families in Uganda. The distribution of SPVD scores was skewed toward highly susceptible categories (SPVD scores 4 and 5), eliminating almost all the resistant genotypes (scores 1 and 2). Likewise, when two promising diallel families (`Tanzania' × `Bikilamaliya' and `Tanzania' × `Wagabolige') were graft inoculated with SPCSV and SPFMV at CIP, severe SPVD was observed in most of the progenies. Individual inoculation of these two families with SPCSV or SPFMV, and Mendelian segregation analysis for resistant vs. susceptible categories led us to hypothesize that resistance to SPCSV and SPFMV was conditioned by two separate recessive genes inherited in a hexasomic or tetradisomic manner. Subsequent molecular marker studies yielded two genetic markers associated with resistance to SPCSV and SPFMV. The AFLP and RAPD markers linked to SPCSV and SPFMV resistance explained 70% and 72% of the variation in resistance, respectively. We propose naming these genes as spcsv1 and spfmv1. Our results also suggest that, in the presence of both of these viruses, additional genes mediate oligogenic or multigenic horizontal (quantitative) effects in the progenies studied for resistance to SPVD.

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Robert O.M. Mwanga, Gerald Kyalo, Gorrettie N. Ssemakula, Charles Niringiye, Benard Yada, Milton A. Otema, Joweria Namakula, Agnes Alajo, Benjamin Kigozi, Rose N.M. Makumbi, Anna-Marie Ball, Wolfgang J. Grüneberg, Jan W. Low and G. Craig Yencho

field resistance to sweetpotato virus disease (SPVD) and alternaria bataticola blight. The two cultivars were bred targeting development of vitamin A–rich (biofortified) orange-fleshed sweetpotato (OFSP). OFSP have been shown to be both effective for

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Scovia Adikini, Settumba B. Mukasa, Robert O.M. Mwanga and Richard W. Gibson

successfully from their fields without serious sweetpotato virus disease (SPVD) infection. In all the reversion studies done so far, the focus has been on SPFMV, and they are limited to vine materials only. It is not clear whether plants infected by SPCSV alone

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Damien Shumbusha, Jean Ndirigwe, Lydia Kankundiye, Anastasie Musabyemungu, Daphrose Gahakwa, Phanuel S. Ndayemeye and Robert O.M. Mwanga

field resistance to sweetpotato virus disease (SPVD) and Alternaria bataticola blight and yield higher (8.3 to 22.8 t·ha −1 ) than the average storage root yield of 6.0 t·ha −1 [ FAOSTAT, 2011 ; International Potato Center (CIP), 1999 ]. Two of the

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Robert O.M. Mwanga, Benson Odongo, Charles Niringiye, Agnes Alajo, Putri E. Abidin, Regina Kapinga, Silver Tumwegamire, Berga Lemaga, James Nsumba and Edward E. Carey

children and women. The cultivars have low to moderate levels of field resistance to sweetpotato virus disease (SPVD) and Alternaria blight ( Tables 2 and 3 ) and high storage root yields compared with the average national root yield of 4 t·ha −1

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Fekadu Gurmu, Shimelis Hussein and Mark Laing

, R.O.M. Yencho, G.C. Moyer, J.W. 2002b Diallel analysis of sweetpotatoes for resistance to sweetpotato virus disease Euphytica 128 237 248 Ndunguru, J. Kapinga, R. Sseruwagi, P. Sayi, B. Mwanga, R. Tumwegamire, S. Rugutu, C. 2009 Assessing the

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R.O.M. Mwanga, B. Odongo, G. Turyamureeba, A. Alajo, G.C. Yencho, R.W. Gibson, N.E.J.M. Smit and E.E. Carey

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R.O.M. Mwanga, B. Odongo, C. Ocitti p'Obwoya, R.W. Gibson, N.E.J.M. Smit and E.E. Carey