Culture of the Root-Lesion Nematode Pratylenchus vulnus on Carrot Disks.

O'Bannon and Taylor reported that carrot disks on 1% agar were suitable for culturing Pratylenchus brachyurus (4). We found that they are suitable also for Pratylenchus vulnus, and easier to prepare than the alfalfa tissue we have used in the past (3). Our observations on carrot disks during the last 3 years may be useful to others. Initially, many of the carrot disks rotted, and a variety of surface-sterilization procedures failed to prevent rotting. Cultures of internal carrot tissue on carrot extract agar or carrot juice agar revealed that apparently healthy carrots had internal infections of Fusarium solani (Mart.) Appel and Wr. and three apparently different, but unidentified, species of bacteria. Bacterial infection of apparently healthy vegetables and the stimulation of bacterial soft rot by Fusarium have been reported (5, 6). The fungus and bacteria caused a fairly rapid soft rot of the de-topped carrots in plastic bags which we obtained from a store, but little soft rot developed over a 3-month period when carrots with tops still attached were purchased. Carrots with tops usually have not been stored as long as those in plastic bags. Storage, especially in a plastic container, is favorable for bacterial and fungal growth. C a r r o t s wi th tops need no t be surface-sterilized. Simply remove the tops, scrub the roots, and allow the excess moisture to evaporate. Then, working in a clean location (we use a laminar flow transfer chamber), pare off the external tissue of a carrot in a spiral pattern, flaming the knife before each contact with the carrot. As a carrot is pared, disks 10-15 mm in thickness are cut with the flamed knife into sterile petri dishes. Five disks are later transferred with flamed forceps to culture jars. This number of disks provides sufficient moisture to eliminate the need for water agar.