Resistance to sweet potato virus disease (SPVD) in wild East African Ipomoea

Sweet potato virus disease (SPVD), the most harmful disease of sweet potato es in East Africa, is caused by mixed infection with sweet potato feathery mottle potyvirus (SPFMV) and sweet potato chlorotic stunt crinivirus (SPCSV ). Wild Ipomoea spp. native to East Africa (I. cairica, I. hildebrandtii, I . involucra and I. wightii) were graft-inoculated with SPVD-affected sweet potato scions. Inoculated plants were monitored for symptom development and tested for SPFMV and SPCSV by grafting to the indicator plant I. setosa, a nd by enzyme-linked immunosorbent assay (ELISA). Virus-free scions of sweet potato cv. Jersey were grafted onto these wild Ipomoea spp. in the field, and scions collected 3 wk later were rooted in the greenhouse and tested fo r viruses using serological tests and bioassays. In all virus tests, I. cai rica and I. involucra were not infected with either SPFMV or SPCSV. I. wigh tii was infected with SPFMV, but not SPCSV, in the field and following expe rimental inoculation; I. hildebrandtii was infected with SPCSV, but not SPF MV, following experimental inoculation. These data provide the first eviden ce of East African wild Ipomoea germplasm resistant to the viruses causing SPVD.