Fungal Spore Germination and Pre-symbiotic Mycelial Growth – Physiological and Genetic Aspects

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs, living symbiotically in the roots of most land plants. They form spores in the soil, which are able to germinate and grow, but are unable to complete their life cycle without establishing a functional symbiosis with a host plant. In this chapter, results of recent studies providing new insights into the main developmental switches occurring in the fungal organism, from the relief of spore dormancy to the development of germlings and growth arrest in the absence of the host, are reviewed. The knowledge of environmental, cytological, biochemical and molecular events involved in early stages of AMF life cycle may reveal how these obligate symbionts compensate for the lack of host-regulated spore germination, possibly representing a strong selective disadvantage. Diverse scientific approaches showed multiple survival strategies, active during pre-symbiotic mycelial growth, contributing to the survival of AM fungal individuals and populations.