32                           PNL Volume 20                       1988 RESEARCH REPORTS
AN ANALYSIS OF THE SYMBI0TIC PROPERTIES OF PEA MUTANTS
Sidorova, K. K. and S. N. Stolyarova
Institute of Cytology and Genetics, Novosibirsk, USSR
According to current concepts, the plant provides the symbiotic fixa­tion of molecular nitrogen needed to cover the energy expenditures of le­gumes.
Experimental mutagenesis appeared promising as a method to produce wider genetic variability for nitrogen fixation in legumes, especially in self-pollinators.
The aim of this study was to analyze the variations in the nitrogen fixation activities of mutants induced by the chemical mutagens EMS, EI, and NMM in the pea varieties 'Parvus' and 'Torsdag'. It was hoped that this analysis would allow us to identify forms with improved symbiotic properties.
The pea plants were grown in pots containing keramsite and vermicu-lite. Before sowing, the seeds were inoculated with a three-day-old cul­ture of Rhizobium leguminosarum. The plants were grown under conditions of nitrogen deficiency. At the beginning of flowering, nitrogen fixation (nitrogenase activity) was determined by the acytelene method in l5-20 plants of each line; stem length, the weight of fresh and dry biomass, and nodule number were also determined.
Nitrogen fixation was estimated as 1.86 mkg N/hr/plant for Parvus; the respective values varied from 0.05-43.45 mkg N/hr/plant for the mutants (Table 1).
On the basis of their nitrogen fixation values, the mutants were as­signed to three groups: Group 1 - decreased as compared with the Initial line (IL) (No. 676, 629, 646, and 630); Group 2 - not different from the IL (No. 653, 1073, 662, 1070, 681, and 614); Group 3 - increased as com­pared with the IL (No. 620, 623, 613, 622, 1087, 612, and 679).
No significant relation was established for nodule number and nitro­gen fixation. However, nodule number was quite high in the mutants of Group 3.
In Group 1 mutants with the lowest nitrogen fixation, the weights of dry biomass were the smallest (No. 676, 629); in those, of Group 3 with the highest nitrogen fixation, the respective values were twice as high (No. 1087, 612, 679).
Four mutants with improved symbiotic properties were identified. 0f these, two had compact stems and dark green leaves (No. 679, 1087), and two were waxless (No. 612, 622).
The estimates for nitrogen fixation varied from 6.6-54.8 mkg N/hr/plant in the mutants induced in Torsdag, the value for Torsdag itself being 19.5 mkg N/hr/plant (Table 2). Five mutants surpassing the original variety in nitrogen fixation were identified. Mutant No. 14, with a maxi­mum nitrogen fixation of 54.8 mkg N/hr/plant, was noteworthy.
Nitrogen fixation was re-estimated in the most outstanding mutants. There was a good agreement between these and the previous estimates.
PNL Volume 20
1988 RESEARCH REPORTS 33
Table 1. Nodule number and estimates for nitrogen fixation in mutants induced in the 'Parvus' variety.
Mutant number
Stem
length
(cm)
Per plant
Fresh
biomass
g
Dry biomass
8
Nodule number
Nitrogen fixation
mkgN/hr
Parvus
127
22.2
4.1
564
1.86
676
124
10.4*
1.6*
4*
0.05*
629
94*
12.4*
1.5*
388*
0.46*
646
133
18.9*
2.5*
203*
1.03*
6 30
106*
22.0
3.1*
138*
1.12*
65 3
129
12.8*
1.7*
72*
2.31
1073
113*
21.1
4.0
514
2.40
662
136*
16.4*
2.4*
104*
2.49
1070
114*
17.5*
3.3*
561
2.90
681
27*
8.4*
1 .4*
29*
3.08
614
131*
17.3*
2.8*
397*
3.14
620
124
17.3*
3.5*
617
6.15*
625
122
16.5*
2.6*
208*
6.29*
613
134*
19.8
3.7
459*
13.94*
622
128
17.0*
3.2*
651
17.00*
1087
70*
26.9*
4.1
271*
26.76*
612
123
19.5*
3.8
364*
27.02*
679
46*
18.8*
3.1*
227*
43.45*
* - The difference from the original variety is significant by Student's
t test.
Tab 2. The estimates for ninrogene fixation in mutants induced in the 'Torsdag' variety.
Mutant
number
Stem length
cm
Per plant
Fresh
biomass
g
Dry biomass
g
Nitrogene
fixation
mkgN/hr
Torsdag
67
4.3
1.1
19.5
3
31*'
4.6
1.1
6.6*
754
72*
10.7*
1.3*
7.7*
1256
76*
10.0
1.3*
11.5*
7
67
9.5
1.3*
12.6*
54
63*
7.8*
0.9
12.8*
1291
71*
10.1
1.5*
14.1*
1310
68
10.2
1.4*
14.6*
955
61
10.2
1.3*
16.5
32
70*
7.9*
1.1
23.3*
1342
75*
9.9
1.4*
23.9*
15
70*
9.4
1.3*
24 .4*
34
54*
7.9*
1.2
27.3*
14
70*
9.6
1.4*
54.8*
* - The difference from the original variety is significant by Student's t test.
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