A greenhouse assay to screen sunflower for resistance to Alternaria helianthi

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi is described. A comparison of conditions led to the following standard conditions being recommended. The first or second pair of leaves of seedling plants at the V8 growth stage are inoculated using inoculum grown on sunflower leaf extract agar for 5–10 days at an inoculum density of 1–2 spores cm² of leaf tissue. A 48 h dew period should be applied to plants covered by a plastic tent. A dew period temperature of 26/26°C night/day and a post-dew period temperature relative to that experienced under local growing conditions should be applied. Lesions are measured 7 days after inoculation, and mean lesion size per plant is calculated. Mean lesion size of lines being tested is expressed as a proportion of the mean lesion size of a susceptible standard included in each screening experiment.