Phases of seed transmission of fusarium oxysporum f sp lycopersici and verticillium dahliae in several tomato cultivars
Phytopathologische Zeitschrift 93(2): 148-163
Seeds of the 3 most important autumn varieties in Morocco ('Eclaireur', 'Monalbo' and 'Exhibition') were examined. The different parts of the fruit cluster (peduncle, vascular tissues of the fruit and seed) were colonized by F. oxysporum f. sp. lycopersici. However, the percentage of infection of these fruit clusters depended on the position of these clusters on the tomato stem and on the variety. The percentage of colonization of the lower fruit clusters was higher than the percentage of colonization of the upper ones. The percentages of Fusarium-contaminated seed of 'Monalbo', 'Eclaireur' and 'Exhibition' were respectively, 41, 19 and 8.5%. All the strains of F. oxysporum isolated from seeds of the three varieties were virulent and belonged to race 1. The pathogen was carried on the seed surface. This contamination was due to the presence of contaminated pulp residues adhering to the seed surface or mixed into the seed lot. The level of contamination of these residues was in direct proportion to the susceptibility of the plant. Under laboratory conditions, all parts of 7-day old seedlings (radicle, hypocotyl, cotyledons) were colonized by F. oxysporum f. sp. lycopersici. Symptoms began to appear at the 7th-15th day up to the 28th day. The ratio between the percentage of contaminated seed and the percentage of plants which actually become infected from the seed-borne pathogen was 1.75, 1.7 and 1.36, for 'Monalbo', 'Eclaireur' and 'Exhibition', respectively. The height of healthy plants was 2-3 times that of wilted plants. V. dahliae was isolated only from the vascular tissue of the lower fruit clusters of 'Eclaireur'. It was not isolated from the other fruit clusters of the same variety nor from those of 'Monalbo' and 'Exhibition'. All the seeds of the 3 varieties were free from this pathogen. F. oxysporum f. sp. lycopersici is a seed-borne fungus.