Characterisation of new symbiotic Medicago truncatula (Gaertn.) mutants, and phenotypic or genotypic complementary information on previously described mutants.

From a pool of Medicago truncatula mutants--obtained by gamma-irradiation or ethyl methanesulfonate mutagenesis--impaired in symbiosis with the N-fixing bacterium Sinorhizobium meliloti, new mutants are described and genetically analysed, and for already reported mutants, complementary data are given on their phenotypic and genetic analysis. Phenotypic data relate to nodulation and mycorrhizal phenotypes. Among the five new mutants, three were classified as [Nod+ Fix- Myc+] and the mutations were ascribed to two loci, Mtsym20 (TRV43, TRV54) and Mtsym21 (TRV49). For the two other new mutants, one was classified as [Nod-/+ Myc+] with a mutation ascribed to gene Mtsym15 (TRV48), and the other as [Nod- Myc-/+] with a mutation ascribed to gene Mtsym16 (TRV58). Genetic analysis of three previously described mutants has shown that [Nod-/+ Myc+] TR74 mutant can be ascribed to gene Mtsym14, and that [Nod-/+ Myc-/+] TR89 and TRV9 mutants are ascribed to gene Mtsym2 (dmi2). Using a detailed analysis of mycorrhizal phenotype, we have observed a delayed typical arbuscular mycorrhizal formation on some mutants that present thick lens-shaped appressoria. This phenotype was called [Myc-/+] and mutants TR25, TR26, TR89, TRV9, P1 and Y6 were reclassified as [Myc-/+]. Mutant P1 was reclassified as [Nod-/+] because of a late nodulation observed on roots of this mutant.