Influence of selection of haploid sporophyte on reaction of diploid maize population exposed to g-irradiation --Rotarenco, VA, Chalyk, ST In our work, maternal haploid plants are used in recurrent selection for improvement of two synthetic populations of maize, SA and SP (Chalyk S. T. and Rotarenco V.A., 1999). Selection of favorable genotypes is carried out at the haploid sporophyte level.

There are no inter-allelic interactions at the haploid sporophyte level, i.e. effects of both dominant and recessive genes are displayed. Thus, an effective natural selection is provoked at the haploid level in a population, which clears up unfavorable mutations. The purification of the population from semilethal and lethal recessive genes has a positive effect on its viability and productivity, as well as significantly enhances its combining ability (Strunikov V.A. 1983; Strunikov V.A., Stepanova N.L., 1983; Seryi A.P., Golovin V.P., 1987).

Our work was aimed at the investigation of the reactions of diploid populations derived through haploid recurrent selection to g-irradiation. To accomplish this, dry seeds of the initial SAC0 population and the results of two selection cycles, SAC1 and SAC2, were irradiated before planting with four doses, 150 Gr, 200Gr, 250Gr and 300Gr. Control and irradiated variants were planted in the field on two-row plots (10m2). Four plant traits were measured after flowering: plant height, ear height, leaf length, and leaf width. Ear traits were measured after harvesting and after drying to normal moisture: seed weight per ear (productivity), ear length, ear diameter, number of seed rows, number of seeds per row, number of seeds per ear, weight of 1,000 seeds, and percentage of seed set. Estimation of the population reaction to irradiation was presented as a ratio to the control. Differences in means between irradiated variants and the control and statistical significance of the differences are presented in the Tables.

Table 1 summarizes the results of the estimation for plant traits and shows that all control for these traits exceeded significantly the means of the irradiation variants, excluding leaf width in the 150 Gr. irradiation variant in the SAC1 population. Reaction of different cycles of haploid selection on g-irradiation was different. A tendency of the reduction of the difference between control and irradiated variants, was observed for three plant traits: plant height, ear height and leaf length in the SAC1 and SAC2 populations in comparison with the SAC0. The SAC2 population should be mentioned specially, as the differences among the controls for almost all the variants of these traits are significantly lower than in the initial SAC0 population.

Table 1. Excess (%) of the control over the means of the irradiated treatments for plant traits.
 
Traits Populations
Irradiation doses 
    150Gr. 200Gr. 250Gr. 300Gr.
Plant Height SAC0 7.1*** 10.7*** 15.4*** 32.7***
  SAC1 8.8*** 16*** 31*** 17.4***
  SAC2 2.5*** 7.4*** 13.7*** 24.6***
Ear Height  SAC0 16.1*** 41.9*** 117.6*** 131.6***
  SAC1 6.5*** 14.8*** 84.8*** 52.7***
  SAC2 3** 9.5*** 29.4*** 77.2***
Leaf Length SAC0 12.5*** 18.5*** 19*** 35.8***
  SAC1 20.9*** 17.5*** 30.9*** 12.9***
  SAC2 4.4*** 14.9*** 27.6*** 24.7***
Leaf Width SAC0 7.3*** 12.1*** 16.8*** 25.1***
  SAC1 -3.2*** 12*** 31.3*** 12.8***
  SAC2 5.3*** 28.6*** 24.8*** 25.3***
**,*** Different from the control at 1% and 0.1% significance level, respectively

Table 2 presents the assessment of the populations for ear traits. As opposed to the plant traits of the populations, the ear traits, to a larger extent, demonstrate the difference in the population reaction to irradiation. Based on productivity as a trait in which all the ear traits are expressed, it can be noted that the differences in relation to the control were significant in all three populations, but in the SAC1 population these differences were negative for three of the four irradiation treatments, i.e. the productivity of the control was lower than in the irradiated treatments. The difference of the productivity of the irradiated variants and the control in SAC2 population were significantly lower than for the SAC0 population. An interesting result was found for the weight of 1,000 seeds in the experimental treatments under study. The mean of this trait increased in all the populations, but in the SAC1 and SAC2 populations this increase was several times higher than in the SAC0 population. We speculated that this is associated with the increase of seed set in the irradiated variants, as compared to the control, but inspection showed that seed set was at the same level for these populations.

Table 2. Excess (%) of the control over the means of the irradiated treatments for ear traits
 
Traits  Populations
Irradiation doses
    150Gr. 200Gr. 250Gr. 300Gr.
Productivity SAC0 52.7*** 49.3*** 250.1*** 254.4***
  SAC1 -36.5*** -11.9*** 24.4*** -18.9***
  SAC2 20.6*** 39.9*** 52.1*** 88.7***
Ear length  SAC0 8.5*** 9.3*** 18.2*** 29.1***
  SAC1 -6.6*** -4*** 2.2 -16.6***
  SAC2 1.3*** 1.2*** 0.8 9.8***
Ear diameter SAC0 6.5*** 8.9*** 18.8*** 27.7***
  SAC1 -7.2*** -1.8** 2.7** 1.2
  SAC2 4.9*** 5.5*** 10.4*** 12.5***
Number of seed rows SAC0 5.4*** 12.8*** 9.3*** 14.3***
  SAC1 0.6 0.08 0.3 1.2
  SAC2 6*** 8*** 12.7*** 14.1***
Number of seeds per row SAC0 19.3*** 23.5*** 36.1*** 46.5***
  SAC1 -3.5** 4.3** 17.9*** -4
  SAC2 7*** 11.3*** 7.3*** 22***
Number of seeds per ear SAC0 39*** 57.3*** 198.7*** 227.6***
  SAC1 5.5** 30.5*** 73.4*** 27.5***
  SAC2 28.5*** 63.2*** 83.6*** 136.7***
Weight of 1,000 seeds SAC0 5.7*** -9.5*** -6* -8.1*
  SAC1 -48*** -43.4*** -49.5*** -59.8***
  SAC2 -9.9*** -19.7*** -24.4*** -29.3***
Seed set SAC0 -248.6 -311.5 -1964 -1619
  SAC1 -137.3 -208.8 -698.3 -1431
  SAC2 -319.2 -574.2 -1076 -1846
*,**,*** Differences from the control at 5%, 1% and 0.1% significance level, respectively

This research allows us to conclude that a combination of artificial and natural selection at the haploid sporophyte level significantly improved a population for plant and ear traits, and enhanced the population's resistance to effects of g-irradiation.
 
 


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