Efficacy of Seedborne Alternaria helianthi on Germination, Seedling Vigour and Blight Incidence in Sunflower

Sunflower seeds collected from Alternaria leaf blight affected plants were tested to detect the pathogen and categorize seeds into apparently healthy, naturally infected (partially infected) and artificially infected (completely infected). All these three categories of infected seeds, naturally infected with A. helianthin and artificially inoculated showed 32.8 and 19.0 per cent reduction in germination respectively. The shoot and root length of seedlings were also reduced in both cases. The vigour index was very low (400) in naturally infected seeds, artificially inoculated seeds recorded a vigour index of 533.5 whereas in control it was 1799.8. With the increase in spore load of A. helianthi on seeds, there was an increase in the number of seedlings showing blight incidence. Seeds were tested to detect the pathogen from the seed coat, endosperm and embryo by a component plating method. In all these three categories of infected seeds, the infection of A. helianthi was more on seed coat than cotyledons and embryos. In cotyledons and embryos of the apparently healthy seeds, the fungal infection was not detected. In partially infected seeds, only cotyledons showed infection while the embryo was found to be free from the pathogen. Completely infected seeds showed the lowest rate of germination (60-64%) in blotter towel and pot culture experiments. Disease incidence was high in completely infected seeds (40%) in the blotter towel test. The fungus is both externally as well as internally seed-borne. The result indicated that the level of seed infection influences germination, seedling vigour and disease incidence in sunflowers