Production of Inoculum and Field Assessment ofAlternaria helianthion Sunflower

Abstract

A. helianthi grew and sporulated better on potato-dextrose agar amended with a sunflower seed extract than on other media tested. Production of inoculum for field and laboratory studies was achieved by culturing the pathogen on filter paper to which a solution containing sucrose and sunflower seed extract had been added. Inoculum produced on the filter paper was stored intact on the mycelium for up to 6 mo. with little loss of viability. A pictorial key based on a percentage scale was developed for the assessment of Alternaria blight on sunflower in the field. Regression analysis showed that the percentage of leaf area infected by A. helianthi for the whole plant was directly proportional to the level of infection on the lowest unsenesced leaves.