Intrathalline distribution of two lichenicolous fungi on Lobaria hosts - an analysis based on quantitative Real-Time PCR

The biology of lichenicolous fungi is still poorly known, including intrathalline hyphal distribution patterns and the density of hyphae these fungi may form within lichen thalli. Since the hyphae of most lichenicolous fungi cannot be morphologically distinguished from those of the lichen mycobiont, we used quantitative Real-Time PCR (qPCR) to detect and quantify lichenicolous fungi and lichen bionts. We investigated the lichenicolous fungi Plectocarpon lichenum and Tremella lobariacearum which inhabit species of the genus Lobaria using the following sample types to determine intrathalline distribution patterns: material with obvious infections, material next to infections, as well as visually uninfected plectenchyma from central and marginal thallus parts. Furthermore, some visually uninfected thalli were sampled for T. lobariacearum. Based on the qPCR data, we show that the two lichenicolous fungi occur predominantly in the symptomatic areas and in a certain area around symptomatic areas. Samples derived from lichen thalli without symptoms of infection showed no evidence of the lichenicolous fungi. We did not observe an alteration of the proportion of lichen bionts in visually infected material. Our data suggest that the structures formed by T. lobariacearum represent galls, whereas those formed by P. lichenum represent stromata. These results raise the question of how intrathalline growth of lichenicolous mycelia might be controlled by the mycobiont.