Nodulation phenotype of 35-day-old wild type (‘Frisson’, 212 + ) and various single- and double-mutant combinations of brassinosteroid-deficient lk and AON mutants Psnark, Psclv2 and Psrdn1. (A) Log of number of nodules per gram dry root weight, (B) space between nodules and (C) photographs of nodules on secondary roots (tertiary roots have been removed); the scale bar is 1 cm. Different letters above bars indicate significant differences between genotypes (ANOVA, P < 0·01). For A and B, values are the mean ± s.e. (n = 6–7).