Studies on Septoria on celery seed

SUMMARY Studies of the relationship between the viability of Septoria on celery seed and the ability of the seed to give rise to infected plants have enabled the effectiveness of various fungicides against celery blight to be readily assessed by tests of treated seed. Seed of differing degrees of infectivity was obtained by storage over a period of 14 months or by various seed disinfection treatments. The germination of spores derived from infected seeds was determined by streaking them on agar and the viability of the ‘total’ fungus (spores and mycelium within the seed) was assessed by inserting seeds into slits in celery petioles. The ability of the seed to give rise to infected seedlings was determined by sowing the seed on compost in seed boxes and retaining glass covers on the boxes for 14 days after seedling emergence. Using the three tests concurrently on stored seed it was shown that the decline in the viability of the ‘total’ fungus was similar to that of the spores and was reflected in the decline in seedling infection. It was thus concluded that tests of the viability of spores from infected seed would indicate the ability of such seed to give rise to infected seedlings and that spore germination tests could be used for assessments of the effectiveness of seed treatments. By this means it was shown that soaking diseased seeds in 0·2% thiram suspension for 24 hr. at 30° C. eliminated infection.