Fusarium resistance in Gladiolus: effects of plant material and testing conditions on the infection of cultivars

Fusarium oxysporum f.sp. gladioli is the most important pathogen of Gladiolus. Cultivation of both corms and flowers is hampered by this fungus. Resistant cultivars are therefore much desired and partial resistance was found within the commercial gladiolus assortment. To assess the Fusarium resistance of cultivars for breeding purposes a standard assay is in use at CPRO-DLO. Genotypes are planted in infested soil. The resistance level is determined six to eight weeks after planting, by calculating the relative length (RL) of the shoots, i.e., length of shoots in infested soil divided by length of shoots in control soil. No information about effects of corm origin, corm size, corm cleaning, temperature or inoculum concentration is known. For Values for Cultivation and Use purposes (VCU) more information is needed about these conditions. Therefore this was investigated in the present study. The disease incidence of a number of cultivars with differing Fusarium resistance was assessed with various corm treatments. In all our experiments, a significant cultivar effect was found. No cultivar by treatment interactions were detected. A significant corm origin effect was also found. For VCU purposes, corms from different growers (mostly breeders), must be cultivated during one year under equal conditions. The corm size had no significant effect on the level of Fusarium infection. Significant corm cleaning effects were found. Dehusking and disinfection of the corm gave a significantly higher infection level. For further tests corm cleaning is not advised, since by damaging the corm secondary infections may occur. Significant temperature and inoculum concentration effects were found. A higher temperature and a higher inoculum concentration gave a higher disease incidence. Both parameters can be manipulated to influence the time course of an assay.