Contrasting sensitivities to seasonal warming among co-occurring diseases

Environmental variation can deviate from a pathogen's optimal conditions for symptom expression and transmission, changing disease dynamics and potentially altering the predominance and distribution of infections across host populations. Here, we assessed the co-occurrence and temperature sensitivity of two common, sterilizing, and persistent diseases of wild Silene vulgaris populations: anther smut (caused by Microbotryum silenes-inflatae) and receptacle smut (caused by Thecaphora melandrii). Using seasonal field surveys and experimental tests of temperature effects on disease expression and infection processes, we show that anther smut is highly sensitive to the summer temperatures experienced in the native range of this host-pathogen system, while co-occurring receptacle smut is not. Anther smut exhibited significantly lower disease prevalence in mid-summer than in spring or autumn seasons, resulting from temporary heat curing of symptoms. Summer temperatures also inhibited infection by anther smut. These results suggest that further environmental warming may lead to changes in the relative impact of these diseases on S. vulgaris, with the temperature-insensitive receptacle smut becoming more dominant in warmer areas or expanding its range to higher elevations where currently only anther smut is common.  This article is part of the theme issue 'Wild plant pathosystems'.