A mutant in Lycopersicon esculentum Mill. with highly reduced VA mycorrhizal colonization: isolation and preliminary characterisation

Abstract

This paper reports the successful isolation and preliminary characterisation of a mutant ofLycopersicon esculentumMill. with highly reduced vesicular-arbuscular (VA) mycorrhizal colonization. The mutation is recessive and has been designatedrmc. Colonization byG. mosseaeis characterised by poor development of external mycelium and a few abnormal appressoria. Vesicles were never formed by this fungus in association with the mutant.Gi. margaritaformed large amounts of external mycelium, complex branched structures and occasional auxiliary cells. Small amounts of internal colonization also occurred. Laser scanning confocal microscopy (LSCM) gave a clear picture of the differences in development ofG. intraradicesandGi. margaritain mutant and wild-type roots and confirmed that the fungus is restricted to the root surface of the mutants. The amenability of tomato for molecular genetic characterisation should enable us to map and clone the mutated gene, and thus identify one of the biochemical bases for inability to establish a normal mycorrhizal symbiosis. The mutant represents a key advance in molecular research on VA mycorrhizal symbiosis.