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.
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.