Three pea mutants with an altered nodulation studied by genetic analysis and grafting

In this study three independently isolated nodulation mutants of pea (Pisum sativum L./cv. Rondo) were compared, i.e.: supernodulating mutant nod3 and the nodulation resistant mutants K5 and K24.

It was observed that the root- and shoot morphology of mutant nod3 were also changed in comparison with the wild type.

Both the altered nodulation and morphology of mutant nod3 appeared to be due to a pleiotropic effect of one mutated gene. Mutant K5 and K24 did not differ morphologically from the wild type.

All mutants were non-allelic, indicating that three different genes were involved. Crossing experiments between nod3 and both nod- mutants showed independent segregation and resulted in the isolation of two different recombinant genotypes.

A difference in nodulation resistance between mutant K5 and K24 was observed. Both mutants did not form nodules when grown in liquid medium, but only mutant K24 showed nodulation resistance when grown in soil. Microscopical investigations on inoculated lateral roots of mutant K5 showed the presence of infection threads, in contrast with mutant K24, where only curling of root hairs was observed.
Grafting showed that the altered nodulation of nod3 and K5 was dependent on the root, while the inhibited nodulation of mutant K24 was dependent on the root and the shoot. Grafting- and adventitious root regeneration experiments showed that the cotyledons were not involved in the mutant characters.