Abstract
A technique was developed for rapidly testing sweet potato seedlings for resistance to leaf scab disease (Elsinoe batatas). Since E. batatas isolates can differ in virulence and aggressiveness, inoculum was derived from field-grown sweet potato vines of different cultivars by incubating stem and petiole sections of heavily-infected cuttings for two days in Petri dishes. A breeding-derived population of seedlings inoculated with a suspension of 3-4 × 103 spores ml-1 could be divided into three groups, heavily infected (43%), moderately infected (36%) and not-infected (21%) seedlings. A field trial showed that 76% of clones derived from not-infected and moderately infected seedlings remained scab-resistant under natural leaf scab epidemics. Of clones derived from heavily infected seedlings, 75% showed susceptible reactions in the field. The test is accurate enough to be used in a breeding programme for scab resistance in sweet potato.
