| Climate change is already influencing the prevalence and distribution of plant disease, posing a potential threat to native species. For plant populations that include mixed ploidy levels, diploids and polyploids may differ in their response to changing abiotic and biotic factors because of divergence in morphology, phenology, or plasticity in these traits. To examine how these factors influence the incidence of powdery mildew, I used diploid and tetraploid Solidago altissima lineages that had been artificially selected to expand the breadth of flowering time and subjected them to contrasting water availability treatments. I also tracked the maternal effects of both water availability and mildew infection on offspring. In general, powdery mildew infection was more widespread in wetter sites and treatments. I also found that ploidy level influenced the amount of powdery mildew cover on the plants, and this may be caused by innate differences in morphology and phenology between diploid and tetraploid cytotypes. Within each ploidy level, the extent of disease damage was higher among earlier flowering genotypes suggesting that advanced flowering phenology may result in increased duration of exposure to pathogens. Finally, maternal infection and water availability has consequences for offspring fitness and robustness. This work indicates that the genetic composition of plants may influence their disease susceptibility in a changing climate, and phenological changes influence plant fitness in response to disease. |
