Sources, survival and transmission of Cladosporium allii and C. allii‐cepae, leaf blotch pathogens of leek and onion

Abstract

Neither Cladosporium allii nor C. allii‐cepae was detected in seed samples of 46 commercial cultivars of leek and nine of onion.In glasshouse tests where flower inflorescences of onions and leeks were dusted with conidia of C. alliicepae and C. allii, respectively, few onion seeds and no leek seeds became contaminated. In field crops of leeks some spathes and inflorescences became diseased and gave 0 002%C. allii contaminated seeds. No infected onion seeds were obtained from naturally‐infected plants in the field.Conidia of both fungi survived for less than 6 weeks in sterile and non‐sterile soil (during which time the temperature varied from ‐8 to +11 C); pseudothecial bodies survived longer.Both pathogens survived for 3 months in debris of onion or leek on the surface of soil in pots under similar conditions. In debris buried at a depth of 7 cm in sterile or unsterile soil they survived for 2 months. Although C. allii survived only 1 month in debris on the soil surfaces following a leek crop, conidia of the fungus were trapped from the air above the area for at least 6 months and healthy leeks transplanted into this area developed the disease. No leaf blotch developed in leeks grown on land which had not previously borne that crop.