Amendment of soil with lime or gypsum and its effect on cavity spot disease of carrots (Daucus carota L.) caused by Pythium coloratum

Glasshouse trials were conducted to examine the effect of lime or gypsum amendments on the development of cavity spot disease of carrots in soil artificially infested with Pythium coloratum. Each amendment was applied to soil from the field at 4000 or 8000 kg/ha. Lime at both application rates significantly (P<0.05) reduced the incidence of the disease. In contrast, both gypsum treatments had no effect on the incidence of cavity spot disease. There was no significant (P>0.05) difference in calcium concentration between carrot roots grown in unamended, lime- or gypsum-amended soil with or without the pathogen. Calcium did not appear to play a direct role in the reduction of cavity spot disease. Under the controlled conditions of this glasshouse trial, reduction in the incidence of cavity spot appeared to be related to the increase in soil pH associated with the application of lime. Field trials at the site of soil collection will confirm whether this mechanism is related to field reduction of the disease following liming.