Allelic relationships of pea nodulation mutants

Thirteen stable nonnodulating mutant lines of pea (Pisum sativum L.) originating from cv. Finale were tested for allelism in pairwise crosses. The F(1) plants were evaluated for the symbiotic phenotype under controlled growth conditions against the nodule bacterium Rhizobium leguminosarum bv. viciae strain 248. All mutations were found to be recessive and the lines were classified into eight complementation groups comprising Risnod1-Risnod23, Risnod8, Risnod9-Risnod22, Risnod14, Risnod19-Risnod25, Risnod20, Risnod24-Risnod26, and Risnod32. Position of Risnod21 was not firmly established, leaving the possibility of allelism both with Risnod19-Risnod25 and Risnod20. The results were partially consistent with the previous reports on the allelism of these lines. Additional crosses confirmed the correspondence of Risnod14 with the locus sym7 and of Risnod19-Risnod25 with sym8. The high number of eight complementation groups formed by 13 mutants provides an indication of additional nodulation loci in pea to those already reported and confirms the complexity of the genetic control of the early stages of nodulation.