XVI International Botanical Congess

The mutualistic mycorrhizal symbiosis between 80% of plant species and the arbuscular mycorrhizal fungi (AMF, Class: Zygomycete) has existed since plants colonized land about 400 million year ago. Theoreticians have predicted that mutualistic symbionts are not subject to either selection pressures favouring the evolution of a sexual life history or evolution of specificity. Ecological studies on the effects of AMF on plant fitness and effects of plant species on AMF life history traits indicate that selection pressures exist which would favour specificity. I will also present data from molecular studies on the genome organization of AMF that give us a clue to evolution of these fungi. Owing to their unusual life history and in the absence of recombination, AMF have possibily evolved to habour a genetically diverse population of nuclei within individuals. Most of the molecular data presented concern the multi-copy ribosomal gene family and the data indicate that the process of concerted evolution my not be acting on this gene family in the AMF. The consequences of the molecular evolution of AMF will be discussed in relation to the evolution of specificity in the mycorrhizal symbiosis.