Abstract

                                Alternaria helianthi, the leaf spot pathogen of sunflower, produced toxic metabo lite in culture, as well as in the infected leaf tissue. The toxin produced necrotic lesions on sunflower leaves. These spots, however, differed from the pathogen produced spots in that, these were not characterized by the yellow halo around. At 2000 ppm, the toxin. inhibited sunflower seed germination by 9 per cent. The shoot and root growth was also inhibited when seeds were treated with the toxin at 1000 ppm. The toxin sprayed at 100 ppm resulted in an initial increase in respiration of leaf tissue. which decreased subse- quently. The effect, in several respects, paralleled the effect of the pathogen on host respiration.

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