SYM 18 - A NOVEL GENE CONDITIONING ALTERED STRAIN SPECIFICITY IN PISUM-SATIVUM CV. SPARKLE

An induced mutant of pea Pisum sativum cv. 'Sparkle' forms few nodules with R. leguminosarum bv. viciea from temperate regions, exemplified by strain PRE, but nodulates normally with some rhizobia from Middle E ast soils, exemplified by strain TOM. The mutant gene is not an allele of sym2, found in the primitive cultivar 'Afghanistan'. Mutant line E 54 has a specificity similar to 'Afghanistan' but forms more nodules w ith temperate strains, especially PF2 which nodulates 'Afghanistan' on ly poorly. The new phenotype is conditioned by gene sym18, which can a ct as recessive or semi-dominant depending on the rhizobial strain. Al so sym18 is distinguished from sym 2 by its location on a different li nkage group. Sym 18 was mapped 9cM from k on linkage group II.