Aspects of resistance to sweet potato virus disease in sweet potato

In field trials during the first and the second rainy season of 1996 in Uga nda, whiteflies were similarly abundant and aphids were absent on three clo nes of sweet potato (NIS-93-63, cv. Tanzania and cv. New Kawogo) although t he three clones differed considerably in their resistance to sweet potato v irus disease (SPVD), a complex disease resulting from infection by both the aphid-borne sweet potato feathery mottle virus (SPFMV) and the whitefly-bo rne sweet potato chlorotic stunt virus (SPCSV). This suggests that vector r esistance does not determine the relative SPVD resistance of these genotype s. SPFMV alone had only a low virus titre in sweet potato cvs Tanzania and New Kawogo, became increasingly difficult to detect in plants of these cult ivars and was seldom acquired by aphids. However, this resistance to SPFMV was not apparent in plants which were also infected with SPCSV, Plants then had a high SPFMV titre, appeared unable to eliminate SPFMV and provided go od sources for aphids to acquire it.