PNL Volume 17 1985 RESEARCH REPORTS

A SEARCH FOR NITROGEN FIXATION MUTANTS OF PEA

Engvild, K. C. Riso National Laboratory, DK-4000, Roskilde Denmark

Mutants of pea that cannot fix N₂ in symbiosis with Rhizobium are

valuable for studies of the physiology and genetics of symbiotic nitrogen

fixation, even though they may not be useful in plant breeding. Nitrogen

fixation mutants are now being investigated in several laboratories (1,

2, 3).

'Finale' (Cebeco, Rotterdam) was chosen for study because of its

stable yields and wide adaptation in many countries. It is a dwarf,

white flowered cultivar with large, round, green seeds and very easy to

handle in growth chambers.

One or 1.5 kg lots of seeds were treated with mutagens (ethyl

methanesulphonate, sodium azide, N-ethyl-N-nitroso urea, and diethyl sul-

phate). The mutagenized seeds were treated with Captan fungicide and

sown wet in the field. The peas from one pod per plant were harvested,

sown in sand in plastic trays, fertilized with P and K and grown in the

greenhouse during winter at about 18C with supplemental fluorescent

light. The trays were inoculated with a mixture of Rhizobium strains.

About 27,000 M₂ plants from different EMS treatments (0.1% EMS over-

night or 0.5% EMS for 1 or 2 hours on pre-soaked seeds) have been

screened. Chlorophyll mutants (1.5-2.7%) were discarded, and plants with

nitrogen deficiency symptoms, yellowing from the root upwards, were exa-

mined for nodulation at the 7-10 leaf stage. Several tentative mutants

have been isolated, and so far three non-nodulating mutants have been

confirmed after retesting. One leaky non-fixing mutant behaves in a very

peculiar way and may not be a nitrogen fixation mutant as such. Non-con-

firmed mutants have been "slow" chlorophyll mutants and plants with no-

dules destroyed by Pythium spp.

1. Jacobsen, E. and W. J. Feenstra. 1984. Plant Sci. Lett.

33:337-344.

2. Kneen, G. E. and T. A. LaRue. 1984. J. Heredity 75:238-240.

3. Messager, A., G. Due, and J. Picard. 1983. Abstract of OECD

workshop "Interactions between carbon dioxide and nitrogen

assimilation in higher plants, Zurich, p. 45.