Another source of the sym2 mutant determining the resistance to nodulation with European strains of Rhizobium leguminosarum bv. viciae

Tsyganov, V.E., Borisov A.Y. and Tikhonovich I.A.

All-Russia Research Institute for Agricultural Microbiology
189620, St. Petersburg, Pushkin 8, Podbelsky sh. 3, Russia

To identify pea genotypes with symbiotic defects 85 pea varieties of different geographical origin from the VIR collection were tested for nodulation and nitrogen fixation ability with commercial strain CIAM 1026. Previously, this set of varieties was analyzed for morphological traits and some of them were subdivided into several lines by Dr. S.M. Rozov (Institute of Cytology and Genetics, Novosibirsk, Russia). Plants of two pea lines: K320-1 (Palestine, P. sativum subsp. humile) and K6047-1 (Afghanistan) were unable to form nodules when grown in quartz sand with N-free nutrient solution. Line K320-1 can form a few nodules per root system when grown in vermiculite with the same nutrition, so its phenotype is not strictly non-nodulating.

Hybridization of variety K320 (Dco) able to nodulate with CIAM 1026 and K320-1 (d) demonstrated monogenic inheritance and recessive manifestation for the K320-1 phenotype. In addition, linkage between this symbiotic gene and locus d was observed (Table 1).

Earlier it was shown that sym2 mutants producing a very low number of nodules when inoculated with European Rhizobium strains are common in pea varieties from the Middle East [1,2,3]. Gene sym2 was localized on the pea linkage group I near d [4]. Allelism tests conducted between lines K320-1 and 31/6 (type line for sym2 used in ARRIAM) showed that line K320-1 is allelic to line 31/6. Thus, the K320-1 line represents yet another naturally occurring source of the sym2 mutant.

Table 1. Segregation data in the F2 population of the cross between line K320-1 (d) and K320 (Dco).

Gene
pair

Phase

Phenotype

Joint
chi-sq.

RCV

SE

A/B

A/b

A/B

a/b

D sym2

C

92

19

16

19

19.1

27.9

4.5

A/a, first locus; B/b, second. *P < 0.0001. The calculations have been made using Rozovís program CROS. Chi-sq. for both genes (3:1) is 0.08, 0.7<P<0.8

1. Young, J.P.W. and Matthews, P. 1982. Heredity. 48:203-210.
2. Kneen, B.E. and LaRue T.A. 1984. Heredity. 52:383-389.
3. Lie, T.A. 1984. Plant and Soil. 82:415-425.
4. Young, J.P.W. 1985. J. Heredity. 76:207-208.