1022-7954/03/3904- $25.00 © 2003
Russian Journal of Genetics, Vol. 39, No. 4, 2003, pp. 406–413. Translated from Genetika, Vol. 39, No. 4, 2003, pp. 501–509.
Original Russian Text Copyright © 2003 by Sidorova, Shumnyi.
Pea is a culture of historical signiﬁcance. In his
experiments conducted on pea, Mendel discovered the
laws of heredity and founded the discipline that was
later named genetics. Since then, pea has been widely
used as a model in genetic, physiological, and other
biological studies. Pea is a primary food crop in many
countries. As a leguminous culture, pea is of a para-
mount importance in producing food and forage plant
proteins. Its nitrogen-ﬁxing properties make it a key
culture in crop rotation.
Developing particular genetics of pea, researchers
have been long focused on studying the above-ground
traits (morphology of stem, leaves, ﬂowers, and
legumes) as well as vegetation period; photoperiod
response; resistance to diseases; productivity-affecting
factors; etc. Only in recent years, their attention
switched to the traits related to root nodule formation
and nitrogen ﬁxation.
To examine symbiotic traits and detect genes
responsible for them, induced mutants obtained by
methods of experimental mutagenesis are generally
used. Spontaneous mutations of symbiotic genes are
rare and difﬁcult to isolate. So far, the highest number
of symbiotic genes was established in pea .
The aim of the present study was creating and study-
ing genetically a collection of symbiotic mutants in pea
L. We examined the following issues:
morphological and biological features of various types
of symbiotic mutants, mode of inheritance of symbiotic
traits, identiﬁcation of symbiotic genes, the ultrastruc-
ture of the bacteroid tissue of root nodules, and identi-
ﬁcation of the plant organ expressing nodulation-con-
trolling genes by means of root/stem grafts.
MATERIALS AND METHODS
Most mutants of out collection were derived from
leguminous cultivar Rondo by exposing seeds to the
chemical mutagen ethylmethane sulfonate. Several
mutants were isolated from the grain cultivar Ramon-
skii 77 treated with nitrosoethylurea. The treatment
methods were described elsewhere .
The mutants were evaluated by symbiotic traits (the
number, size, and color of root nodules; nitrogenase
activity) and morphological traits (stem height and
shape, vegetative biomass amount, the number of roots,
root length). Seed productivity was estimated when
Each isolated mutant was homozygous for one
mutation but could be heterozygous for one or more
other mutations. Therefore, examining each symbiotic
mutant up to generations M
, we discarded all
mutants appearing in the same family M
that the iso-
lated symbiotic mutant. Only stable mutant lines of
were included in hybrid analysis.
For further examination, phenotypically mutant plants
isolated in F
from the cross with the original cultivar
Experiments were conducted in the greenhouse.
Plants were grown on shelves in pots under two regimes
of mineral nutrition (with or without nitrogen; in the
latter case, only a start dose of nitrogen was introduced
at the beginning of the plant growth at the amount of 0.2
of the norm. The plants were inoculated as seedlings
A Collection of Symbiotic Mutants in Pea
Creation and Genetic Study
K. K. Sidorova and V. K. Shumnyi
Institute of Cytology and Genetics, Russian Academy of Sciences, Novosibirsk, 630090 Russia;
fax: (3832) 33-12-78; e-mail: firstname.lastname@example.org
Received October 31, 2001; in ﬁnal form, March 6, 2002
—A collection of symbiotic pea mutants consisting of 34 lines was created. The morphobiological and
symbiotic description of different types of pea mutants is presented. The mode of inheritance of symbiotic char-
acters is analyzed. For the ﬁrst time in pea, hypernodulation mutations with dominant inheritance were isolated.
Differences in the structure of bacteroid tissues of root nodules were revealed between mutants with effective
and ineffective nodules. Using reciprocal root/stem and stem/root grafts, the plant organ producing nodulation-
controlling factors was established. New hypernodulation-controlling genes—
For the ﬁrst time in pea, using pure lines derived from cultivars with contrasting nodulation, the new gene
was found. The dominant allele of this gene controls abundant nodulation, high nitrogen ﬁxation, and
nitrate resistance. Pea cultivars carrying the
gene that can be used in selection for improved symbiotic
properties were identiﬁed.