Abstract
Abstract A description is provided for Didymella lycopersici . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Lycopersicon esculentum . DISEASE: Stem and fruit rot of tomato. A girdling canker, dark brown and sunken, develops at, or just above, soil level. Secondary cankers may later develop higher up the stem. The plant collapses and dies. The soft, outer diseased tissues contain numerous pycnidia and in damp conditions conidia are extruded in slimy pink masses. The perfect state is rarely found (24: 78; 35: 349). Infection can occur on roots, leaves and flowers. Fruit is also attacked. GEOGRAPHICAL DISTRIBUTION: Widespread (CMI Map 324, ed. 2, 1968). TRANSMISSION: Infection arises via conidia from infected organic material in the soil, usually host debris or composting waste. This is probably the main source of infection (36: 138) and the pathogen overwinters readily in such debris. Air dispersal by ascospores appears less important than splash and soil dispersal by conidia (39: 626). Seed transmission is considered less important. Hyphae and pycnidia are found within the hairy seed coat (9: 70; 24: 480; 34: 554; 40: 386). More seed transmission occurs in Jan. sowings than in Mar. and Apr. (41: 546). Conidia do not survive more than 9 months on the surface of seed (36: 138).
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