CHISINAU, MOLDOVA
Institute of Genetics and Physiology

 

Gamma - irradiation of seeds with haploid and diploid embryos

 

-- Rotarenco, VA, Maslobrod, SN, Romanova IM, Mihailov, ME

 

Haploid plants have recently gained a wider utilization in maize breeding programs. This is feasible after high-effective inducers of maternal haploids have been discovered (Coe, 1959).

            All the genes, both dominant and recessive are expressed at the level of haploid plants due to the absence of the second gene allele. Thus, the use of haploids for induced mutagenesis may allow a significantly efficient identification of mutations. In addition, a higher mutation number may appear at the level of haploid plants in comparison with diploids – the reduction of gene-reparation efficiency in haploids might be one of the possible reasons.    

            In order to induce mutations in haploids, their reaction to a mutagenic factor should be evaluated.

            The aim of this work was to establish the impact of different g-irradiation doses on the seeds with haploid embryo. Both haploid and diploid seeds of the heterogeneous SA population were irradiated. Dry seeds were irradiated at doses of 20, 40, 60, 80 and 100Gy. Soaked seeds (24 hours) were irradiated at doses of 2, 4, 6, 8 and 10Gy. 50 kernels were used in each treatment. Following irradiation, seeds were divided into two replications and grown up in a thermostat for 4 days (28¡C). Root (main root) and coleoptile length were measured in seedlings, and the number of roots was counted. The results of the experiment are shown in the Table.

            The irradiation of haploid seeds (soaked) resulted in a significant decrease of root length at the doses of 4, 6, 8 and 10Gy as compared with control. A similar regularity was found for coleoptile length; however, significant differences were observed only at the doses of 6 and 10Gy. This tendency was maintained for the parameter of root number, but the differences were not significant. The dose of 2Gy showed a tendency to stimulation for the three indices mentioned.

            The irradiation of haploid-dry seeds resulted in a decrease of root length accompanied by intensification of the inhibiting effect beginning from the dose of 40Gy to 100Gy. As for coleoptile length, a significant difference at the dose of 100Gy was found. A significant reduction was discovered for root number beginning from the dose of 40Gy. A tendency toward stimulation was traced at the dose of 20Gy.

 

 

The parameters of 4-day seedlings after g-irradiation of seeds

                                          Haploids

Diploids

#

Dose,

Gy

Length of

coleoptile,

mm

Length of root,

mm

Number of roots,

no.

Length of

coleoptile,

mm

Length of root,

mm

Number of roots,

no.

Soaked seeds

1

Control

53.0±4.97

104.4±6.81

3.4±0.23

70.4±4.62

124.6±7.61

3.7±0.27

2

2

60.8±3.97

107.0±3.43

3.6±0.18

73.1±4.36

133.4±6.54

3.9±0.18

3

4

55.0±4.89

75.9**±5.79

3.0±0.22

71.9±3.66

132.1±4.70

4.3±0.18

4

6

42.5*±4.26

66.3***±5.49

3.0±0.22

73.1±5.11

114.6±7.42

3.3±0.20

5

8

53.0±3.26

76.0**±5.94

3.3±0.17

78.0±3.47

118.5±5.43

4.1±0.16

6

10

44.6*±2.92

50.7***±4.42

3.0±0.16

54.2*±5.25

75.3***±7.50

2.8*±0.26

Dry seeds

1

Control

23.7±2.56

71.3±3.79

3.1±0.15

28.2±2.85

74.3±6.06

3.0±0.19

2

20

29.0±2.83

69.2±3.59

3.4±0.14

38.3±2.70

90.2*±4.58

3.3±0.15

3

40

18.9±2.05

49.1***±3.80

2.7±0.17

31.7±2.43

86.5±5.12

2.9±0.17

4

60

21.9±2.26

40.4***±3.30

2.3***±0.18

34.3±2.99

76.3±5.88

3.0±0.24

5

80

17.6±2.19

41.0***±3.06

2.3***±0.16

29.9*±2.74

79.9±5.23

2.9±0.19

6

100

11.0**±2.00

27.7***±2.62

1.8***±0.16

19.5*±2.23

53.1**±5.06

1.8**±0.16

 

 

 

 

 

 

 

 

 

 

 

 

 

*,  **, *** significant at 5%, 1% and 0.1% level, respectively. 

 

The irradiation of diploid seeds (soaked) resulted in a decrease of root length beginning from 6Gy; however, a significant difference was observed only at 10Gy. A similar trend towards stimulation at the dose of up to 8Gy and a significant decrease at 10Gy was found for coleoptile length. A similar regularity was discovered for root number. The tendency towards the stimulating effect was observed up to 4Gy for root length, and up to 8Gy for coleoptile length and root number.

            The irradiation of diploid-dry seeds yielded an increase of root length, the reliable increase being found at 20Gy and 40Gy. The dose of 100Gy yielded a significant decrease. The tendency towards stimulation was observed at the dose of up to 80Gy for coleoptile length, but the significant stimulation was established at the dose of 20Gy. A significant decrease was found at the dose of 100Gy. A significant decrease was observed at 100Gy for root number.

            There were not observed any significant differences in germination rate between the treatments and regardless the ploidy of kernels, and on average it was 95%.

Based on the results obtained, some conclusions can be done: a significant difference in sensitivity to irradiation was recorded in haploids in comparison with diploids; a stimulation of seedling growth has been found at minimal doses of irradiation of both diploid and haploid seeds, however, the stimulation was insignificant in the most cases. The experiment carried out allows us to identify acting doses of g-irradiation that will be employed to induce genetic variation using haploids.