PEA LINES CARRYING SYM1 OR SYM2 CAN BE NODULATED BY RHIZOBIUM STRAINSCONTAINING NODX - SYML AND SYM2 ARE ALLELIC

In wild pea varieties two genes, sym1 and sym2, have been identified t hat cause resistance to European Rhizobium leguminosarum by. viciae (R lv) strains. The sym2 gene has previously been studied in some detail and it was shown that the additional nodulation gene nodX is sufficien t to overcome the sym2 controlled nodulation resistance. Here we chara cterize the sym1 gene. We show that the resistance conferred by sym1 c an be overcome by the introduction of nodX in European Rlv strains, in dicating that sym1 just as sym2 is involved in Nod factor recognition. Both sym1 and sym2 display a recessive or dominant nature depending o n the Rlv strain used for inoculation. Furthermore, introgression line s containing either sym1 or sym2 are able to form nodules with Rlv str ain 248 at 26 degrees C, but not at 18 degrees C, indicating that both sym1 and sym2 have a temperature sensitive nature. sym2 was mapped on the pea RFLP map. We found that sym1 maps in the same region of chrom osome 1 as sym2. By crossing sym1 and sym2 containing introgression li nes we demonstrate that sym1 and sym2 are allelic.