Influence of Inoculum Density of Fusarium oxysporum f. sp. cyclaminis and Sodium Chloride on Cyclamen and the Development of Fusarium Wilt.

The influence of soil densities of Fusarium oxysporum f. sp. cyclaminis on development of Fusarium wilt of cyclamen (Cyclamen persicum) was evaluated by adding increasing amounts of F. oxysporum f. sp. cyclaminis-colonized millet inoculum to potting mix planted to cyclamen. Additions of inoculum resulted in an increase in the CFU of F. oxysporum f. sp. cyclaminis per ml of potting mix and an increase in vascular discoloration of the corm of cyclamens after 10 weeks. A threshold of 5 × 104 CFU/ml of potting mix was needed to consistently cause vascular discoloration in the corms. Final fresh leaf weights declined to 30% of the leaf weights of the control when inoculum was added at 105 CFU/ml of potting mix. The effect of NaCl on Fusarium wilt was also examined, as anecdotal reports from cyclamen producers suggest that NaCl applications may improve plant growth. When NaCl was applied to potting mix at rates of 0.25 and 0.50 g/liter of potting mix, final fresh weights were greater and the area under the disease progress curve values were less than those of control plants. However, final disease severity was not affected. In the absence of the pathogen, leaf weights were greater when NaCl was added at 0.25 g/liter of potting mix. Disease development and the effectiveness of NaCl on disease were not affected by potting mix pH 5.1 to 7.2. Cyclamens grown in potting mix with a pH of 7.2 had chlorotic leaves, but with the addition of NaCl, the chlorosis was not observed. Leaf analyses showed that the addition of NaCl increased foliar levels of Na, Cl, and Mn, but decreased foliar levels of P, Ca, Mg, S, and B. Sodium chloride applied at 0.25 to 0.50 g/liter of potting mix had growth benefits, but disease suppression was marginal.