Plant Pathology Department, Faculty of Agriculture, Mansoura University, Egypt; 2Danish Government Institute of Seed Pathology, Hellerup, 2900 DK, Copenhagen, Denmark

Background and objectives
Fusarium wilt is a devastating disease that occurs in tomato-growing regions of the world. Seeds provide an effective source of infection by pathogens in new geographical areas as well as in successive seasons. Tomato seeds are exchanged throughout the world by commercial activities. Although increasingly sensitive seed testing techniques are being developed and used, seed health testing for seedborne pathogens can never certify that there is absolutely no contamination. In the present investigation we describe the role of tomato seeds in dissemination of fusarium wilt and fusarium crown and root rot diseases. Seed samples resembling local and imported cultivars commonly grown in Egypt were examined for health by routine testing techniques. This paper reports the detection of races 1 and 2 of the fusarium wilt pathogen and Fusarium oxysporum f.sp. radicis-lycopersici from naturally infected tomato seeds. Aspects of race identification, pathogenicity testing and cultivar resistance were investigated. Determination of purity, germination and optimum method for detection of Fusarium species were also studied.

Results and conclusions
Of 83 seed lots, 19% were infected with F. oxysporum. Percentage of infection ranged from 1 to 22%. Based upon pathogenicity tests and race identification using tomato differential cultivars, two races, 1 and 2, of Fusarium oxysporum f.sp. lycopersici were identified.

Greenhouse results showed that the resistance reaction of nine tomato cultivars against races 1 and 2 of the fungus demonstrated that two cultivars, namely Flora Dade and Pomo Doro, were resistant to race 1, while cultivars Peto 86 and Super Marmand were resistant to race 2. Only strain B cultivar was resistant to both races. The other cultivars were either susceptible or moderately resistant to races 1 and 2.

Data obtained from purity and germination tests of heavily infected seed lots with F. oxysporum revealed that samples with more inert matter yielded more seed infection and less germination. In seed health, testing of tomato seeds is very important to determine the pathogenicity of any Fusarium colony associated with the seeds, because most colonies are saprophytes and similar in character to the pathogenic ones. It was difficult to detect such internal slow-growing fungi by the blotter method, but specific agar medium was sensitive in detecting Fusarium species. During the pathogenicity test on F. oxysporum f.sp. lycopersici isolates, one isolate produced crown and root rot symptoms. The isolate was identified as F. oxysporum f.sp. radicis-lycopersici. All the tomato cultivars under investigation were susceptible to this isolate.