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Complete Resistance by Carnation Cultivars to Fusarium Wilt Induced by Fusarium oxysporum f. sp. dianthi Race 2

The response of two carnation (Dianthus caryophyllus) cultivars, Arbel and Scarlette, to Fusarium wilt induced by Fusarium oxysporum f. sp. dianthi race 2 was determined in experiments conducted in an infested field and using artificially inoculated plants grown in a net-house. In six field experiments conducted from 1989-90 to 1995-96, and including more than 200 different cultivars, Arbel and Scarlette were the only ones that remained symptomless. The responses of the other cultivars varied markedly, but even those known to be highly resistant, Eveline and Novada, were frequently diseased. In the net-house tests, Arbel and Scarlette were compared with cultivars that ranged in their response to Fusarium wilt from highly resistant to highly susceptible. Due to the conducive conditions for Fusarium wilt prevailing in these tests, disease progressed rapidly, and by the end of the experiments all cultivars except Arbel and Scarlette were severely diseased (incidence of 81.2 to 100%); Arbel and Scarlette remained symptomless. The pathogen did colonize the basal stem parts of all cultivars, including Arbel and Scarlette. The number of colony-forming units (CFU) recovered from the basal stem parts was 10⁵ CFU/g of stem in the other cultivars, 10³ CFU/g in Scarlette, and 50 CFU/g in Arbel. Results of our study suggest that Arbel and Scarlette exhibit a novel type of resistance to Fusarium wilt induced by F. oxysporum f. sp. dianthi race 2.