Non-pathogenic
Fusarium oxysporum S3HO3, isolated from the root surface of healthy spinach growing in a field infested with Fusarium wilt, cross-protected against
F. oxysporum f. sp.
spinaciae, when the soil was amended with the isolate before infestation with the pathogen. This cross-protection, however, did not continue through the harvesting. In order to extend the duration of disease suppression, pre-treatment of spinach seedlings with non-pathogenic
F. oxysporum S3HO3 was combined with subsequent transplanting to reduce disease development. The most effective pre-treatment method for seedlings was mixing a bud-cell suspension (10
6 cfu/dry soil g) with nursery soil before sowing and then seedlings were grown 15 days before transplanting. Disease suppression then lasted through harvesting with a protective value of 96.3 when pre-treated seedlings were transplanted in infested soil. On the other hand, when nursery soil was drenched with a bud-cell suspension (10
7 budcells/ml, 1/10, v/w) 10 days after sowing (5 days before transplanting) and pre-treated seedlings were transplanted, the protective value (87.1) was higher than drenching at earlier stage such as 1 or 5 days after sowing. Although the drenching method was easier and more practical, its protective value was less than that of the soil-mixing method. Non-pathogenic
F. oxysporum S3HO3 was not pathogenic to spinach, cucumber, melon, water-melon, tomato, lettuce, garland chrysanthemum, carrot, Japanese hornwort and some
Brassica spp. Practical control of Fusarium wilt of spinach by transplanting seedlings grown in nursery soil containing non-pathogenic
F. oxysporum S3HO3 was tested in the field. The protective effect of this method was even greater than that obtained by direct sowing, more effective than transplanting without inoculation with non-pathogenic
F. oxysporum S3HO3 and as effective as solar heating sterilization in a closed vinyl house in summer, when pre-treated seedlings were transplanted in naturally infested soil in vinyl house. The protection in the field lasted through harvesting. These results suggest that control of Fusarium wilt of spinach by transplanting spinach pre-inoculated with non-pathogenic
F. oxysporum S3HO3 should be practical.
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