MUTANTS DEFECTIVE IN SYMBIOTIC NITROGEN FIXATION

PNL Volume 19

1987

RESEARCH REPORTS

Kneen, B. E.
and T. A. LaRue

Boyce Thompson Institute
Ithaca, NY 14853-1801 USA

Variants in the symbionts are required to delineate the steps
in the process of nodule formation and function. Using EMS and
gamma radiation, we induced mutants of the pea cultivar 'Sparkle'
which are defective in nodulation (2). We previously reported
four loci (sym-5, sym-7, sym-8, and sym-9) controlling
non-nodulation in these mutants (3). We have since obtained addi-
tional mutants by neutron radiation. Two monogenic recessive mu-
tations, in selections N15 and N24, are not nodulated by any
strain of Rhizobium leguminosarum tested, and are not allelic with
those previously described. We designate these loci as sym-10 and
sym-11.

Jacobsen (1) obtained EMS-derived mutants of cv. 'Rondo'.
The gene controlling defective nodulation in his selection K5 is
non-allelic with our mutants, and is designated sym-12.

Although line E135 was selected in the M2 generation as a
nodulating but non-fixing plant, its M3 progeny segregated both
non-nodulating and nodulating, non-fixing plants. The non-fixing
segregant forms abundant small, white nodules lacking nitrogenase
(acetylene reduction) activity. In crosses between wild-type and
a true-breeding pure-line, nodulating, non-fix line, the F2
segregated 3:1 fix:non-fix. The gene controlling the fixation
phenotype is designated sym-13. The F2 progeny of the non-
nodulating egregant crossed with its wild-type parent, Sparkle,
segregated for both nodulation and fixation, indicating the non-
nod line also carried alleles for non-fixing. Allelism tests are
in progress involving this non-nod segregant and other non-nodula-
ting lines.

1. Jacobsen, E. 1984. Plant and Soil 82:427-438.

2. Kneen, B. E., T. A. LaRue, and N. Weeden. 1984. PNL 16:31-34.

3. Kneen, B. E. and T. A. LaRue. 1986. PNL 18:33.

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