A toothpick inoculation method for evaluating carrot cultivars for resistance to Alternaria radicina

The susceptibility of 46 carrot cultivars to infection by Alternaria radici na Meier, Drechsler, and Eddy, causal agent of black rot disease, was evalu ated in field trials with a toothpick inoculation method. Toothpicks infest ed with A. radicina were inserted into the shoulders of 10- to 12-week-old carrots (Daucus carota L.) and lesion areas were measured 9 to 10 weeks lat er. There were significant differences in lesion size among cultivars. Rela tively resistant cultivars included 'Panther' and 'Caro-pak', and susceptib le cultivars included 'Royal Chantenay' and 'Nogales'. Nine of the cultivar s were inoculated with A. radicina-infested toothpicks and maintained in co ld-storage for 10 weeks. Lesion development was greater in cold-storage tha n in the field, but the relative ranking of cultivars in terms of resistanc e to A. radicina was similar.