Conditions for germination of Pycnidiospores of Septoria Apiicola Speg.

Summary The effect of temperature and relative humidity on germination and growth of germ tubes of pycnidiospores of the fungus Septoria apiicola Speg. on different substrates was studied. The optimum temperature for germination was 20.0° to 22.5°c but spores germinated readily between 5.0° and 27.5°c. Free water was not essential. either for germination or for infection of celery leaves (cultivar Utah 52/70). On a clean glass surface spores germinated at relative humidities down to 96.8% but failed to do so at or below 96.0%. On celery leaves good germination occurred at relative humidities down to 94.5%; a few spores produced germ tubes at 80.0% but these failed to continue growth and disease symptoms were not evident 10 days after inoculation.