Phenotypic characterization of sym8 and sym9, two genes conditioning non-nodulation in Pisum sativum 'Sparkle'

Two non-nodulating and non-allelic mutants of P. sativum (L.) 'Sparkle', R25 (sym8) and R72 (sym9), were obtained by γ-radiation. Non-nodulation in each mutant was conditioned by a single recessive gene. Growth analysis indicated that if the mutants were provided with adequate fixed nitrogen, they both had the same growth rate as their nodulating parent, 'Sparkle'. Reciprocal grafts between mutants and parent plants indicated that non-nodulation was controlled by the root genotype. Both mutants induced the common nod genes in rhizobia, and had either higher or similar numbers of rhizobia attached to their roots as had 'Sparkle'. Microscopic studies indicated that root hairs of R72 deformed after inoculation, whereas root hairs of R25 did not show such deformation. In both mutants hair curling, infection thread formation, and nodule meristem initiation did not occur. Key words: mutants, sym genes, nodulation stages, symbiosis.