PNL Volume 18 1986 RESEARCH REPORTS

ADDITIONAL MUTANTS DEFECTIVE IN NODULATION

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

Boyce Thompson Institute, Ithaca, NY 14853 USA

The availability of both bacterial and plant mutants defective in

nodulation and fixation is essential to studying the molecular basis of

nitrogen fixing symbioses. To obtain host mutants, seeds of Pisum sativum

cv 'Sparkle' were treated with gamma radiation or EMS. M2 populations were

screened with Rhizobium leguminosarum strain 128C53 for nodulation defec-

tive plants, and selections which were stable and fertile to M3 are being

characterized. We found well nodulated Ineffective mutants which have

little or no nitrogenase (C₂H₂ ) activity. There are 29 selections with few

or no nodules; four of these have shortened roots and/or shoots. F1 and F2

progeny from reciprocal crosses among mutants are being examined to deter-

mine allelism.

Six mutants, five obtained by EMS and one by gamma radiation, are allelic

with the sym-5 gene of our first reported non-nod mutant (2). The reason

for the high frequency of mutation at this locus is unknown.

Three new non-nodulating lines have single gene recessive mutations at

unique loci. All the F1 plants from crosses between the mutants and

Sparkle or 'Rondo' nodulate, and segregation of the progenies ap-

proximates 3:1 non:non-nod. Crosses among selections E69, R2 5, R72, and

sym-2 ('Afghanistan' [3]) and sym-5 lines yield F1 nodulating plants. The

new loci are designated sym-7, sym-8, and sym-9. Two mutants, one from EMS

and one from gamma radiation, are allelic at sym-8. None of these mutants

exhibits strain specificity in infectivity tests with nine strains of _R.

leguminosarum including four Middle Eastern strains. The non-nodulating

phenotypes were not temperature dependent in an experiment comparing plants

grown at a 2 5C/20C day/night regime or plants whose roots were kept at 9C

with plants grown at the normal 20C/15C regime.

Two mutants with few nodules and abnormal roots are monogenic reces-

sives, based on crosses with Sparkle or 'Trapper'. R50 has shortened

internodes and shortened lower lateral roots. The leaves are pale with

raised veins. Very few (0-5) white nodules are found near the crown of the

roots. E151 appears normal in shoot growth, but the lower lateral roots

are variable in length, averaging approximately one-half that of Sparkle.

The number of pale pink or white nodules varies (0-30). These low nodula-

tion phenotypes are always associated with shortened roots in segregating

F2 populations.

Jacobsen (I) found two nodulation defective EMS-induced mutants of

Rondo: K5 and K24.We are crossing these selections with our mutant lines

to determine if they are allelic.

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

2. Kneen, B. E. 1984. J. Heredity 75:238-240.

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

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