VIEW ARTICLE

Ecology and Epidemiology

Effects of Initial Inoculum and Cultivar Resistance on Incidence of Fusarium Wilt and Population Densities of Fusarium oxysporum f. sp. dianthi on Carnation and in Soil. Y. Ben- Yephet, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel; M. Reuven, A. Zviebil, and D. Shtienberg. Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Phytopathology 86:751-756. Accepted for publication 10 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-751.

The effects of initial inoculum and cultivar resistance on the incidence of Fusarium wilt and the population densities of Fusarium oxysporum f. sp. dianthi on carnation and in soil were studied in the field and in large containers filled with naturally infested soil. Five carnation cultivars that ranged in their response to Fusarium wilt from completely resistant (‘Scarlette’), highly resistant (‘Eveline’), moderately resistant (‘Galit’), susceptible (‘Lior’), to highly susceptible (‘Hermon’) were included in all experiments. In the field, Fusarium wilt incidence and counts of CFU of F. oxysporum f. sp. dianthi recovered from soil or plants increased with time. The magnitude of that increase and the final population density of the pathogen, however, were affected by the degree of cultivar resistance. For example, the number of CFU of the pathogen on stems of cultivar Hermon was 10,000-fold higher than that on cultivar Scarlette. Population densities of the pathogen on plant stems were linearly related to disease incidence; the more severe the disease, the larger the number of CFU of F. oxysporum f. sp. dianthi recovered. The pathogen also was recovered (about 10⁴ CFU/g of plant) from symptomless plants. A similar relationship was observed in soil, sampled from beneath plants, except that the increase in CFU was not linear and pathogen CFU leveled off gradually at high disease incidence. In containers, disease incidence increased significantly (P < 0.05) with increasing initial inoculum levels for the susceptible, but not for the resistant, cultivars. The number of F. oxysporum f. sp. dianthi CFU in soil increased for the cultivars Hermon, Lior, and Galit, but not for ‘Eveline’ or ‘Scarlette’; in the stems, the number of CFU increased for all cultivars.