Appendix B. The fungicide Ridomil Gold has no effect on plant fitness in the absence of Coleosporium ipomoeae.
Results from the main experiments of 2000 – 2002 describe the deleterious effects of Coleosporium ipomoeae on Ipomoea purpurea fitness. The purpose of this supplementary experiment was to determine if the fungicide Ridomil Gold affects plant fitness in the absence of C. ipomoeae.
Materials and Methods
The following experiment was conducted at a different field site than that used in the main experiments of 2000 – 2002. In 2000, a total of 288 seeds (96 seeds of each resistance locus genotype) were planted using a randomized block design at 0.75 m × 1 m intervals and were allowed to twine up 2 m wooden stakes. Seeds were randomly assigned to a control or pathogen exclusion treatment, administered in the same manner described for the main experiment of 2000. C. ipomoeae damage was measured as the absolute number of uredia that developed on plant leaves. All leaves were counted as an estimate of plant size and seeds were counted as an estimate of plant fitness. Data for leaf number and seed number were log transformed for statistical analyses to improve the fit of residuals to a normal distribution. Ridomil Gold was obtained as a gift from Novartis Crop Protection, Inc, Greensboro, North Carolina, USA.
Germination and survival was low at this site and only 236 seeds germinated, of which 187 grew to maturation. There was no significant difference between treatments for the number of plants that germinated but failed to produce seeds (23 control plants vs. 26 treated with Ridomil Gold: X 2 = 0.18, χ 2 0.05, 1 = 3.814). Of the plants that grew to maturation, six susceptible plants in the control treatment exhibited a single C. ipomoeae uredium and three susceptible plants exhibited two uredia, representing a negligible fraction of leaf area. Leaf number and seed number were analyzed for all adult plants using block, treatment, and genotype as fixed main effects in an ANOVA. There was no evidence that the fungicide used in the main experiments of 2000 – 2002 had any detectable effect on I. purpurea leaf number (F = 0.03, df = 1, 180, P = 0.8719) (Fig. B1) or seed number (F = 0.05, df = 1, 180, P = 0.8306) (Fig B2). These qualitative results are not influenced by the removal of the 9 plants exhibiting C. ipomoeae damage. This experiment indicates that the fungicide used to reduce the infection load of C. ipomoeae in the pathogen exclusion treatments of the main experiments of 2000 – 2002 had no detectable effect on the performance of I. purpurea. Consequently, differences observed between the control and pathogen addition treatments relative to the pathogen exclusion treatments can be ascribed to the effects of C. ipomoeae.
|FIG. B1. Ridimal Gold has no effect on leaf number.|
|FIG. B2. Ridimal Gold has no effect on seed number.|