The comparative characteristic of the correlation between the traits of maize diploids and haploids --Rotarenco,VA Plant transition from the diploid to haploid level involves quite notable phenotypical modifications. Haploids, as a rule, are similar to the specimens of the initial species for major traits, but in most cases their difference from diploids is of quantitative nature. It is believed that haploids are a reduced copy of parental form, at the same time, the transition to the haploid level involves significant modifications of genotypical medium, gene dose, expression of recessive gene. These peculiar features of haploids cause a definite specificity in gene interaction, as well as in genotype one , or more precisely, that of the genome and the environment. Some researchers (Hollingshead, 1930; Muntzing, 1934; Katayama, 1954) have found among the haploids traits absent in the initial diploids in a number of crops. The correlation between different traits is likely to vary in haploids and diploids, too.

The trait conjunction is a complex property from the genetic and physiologic viewpoints. Much attention is paid to the interrelation of the expression of different traits in both breeding work and genetic studies. Every possible correlation of traits is at the same time a property which hampers the breeding process, as well as an obstacle to developing an expected ideotype.

The goal of our work was to compare the interrelation of some qualitative traits, as well as the comparison of the relations between the indices including plant and earcorn traits at the diploid and haploid level.

The heterogeneous SP population and haploids derived from it were used as initial material for our studies. The plant traits were measured in diploid and haploid population after the termination of growth. The earcorn traits were measured after their maturation under laboratory conditions. These were followed by the calculation of correlation coefficients and the criteria of their significance.

The correlation coefficients presented in Table 1 show that the pairs of the plant traits have a mean correlation between each other. The comparison of two levels of ploidy with the respect to these traits and their relation shows that the correlation coefficients differ insignificantly. A significant difference between the diploid and haploid levels was recorded for earcorn length and diameter. The correlation coefficient for the earcorn traits was 0.63 in the diploid population and 0.21 in the haploid one.

The earcorn traits are very important for maize haploids as their yielding potential can be predicted from them. This is associated with the dominance of the abnormal meiosis in the haploid chromosome set and the formation of a low number of seeds.

Table 1. The coefficients of correlation between certain plant and ear traits in diploids and haploids.
Correlating Traits 2n n
Plant Height and Height of Attachment of the First Ear 0.53** 0.59**
Leaf Length and Width 0.4** 0.43**
Ear Length and Diameter  0.63** 0.21

*,** The coefficients of correlation are significant at P>0.05 and 0.01 respectively.

Table 2 shows the correlation coefficients between the traits of the earcorn and plant at the diploid and haploid level. The data show a mean correlation of these traits in the diploid plants and actually the absence of the correlation in the haploids.

Table 2. The coefficients of correlation between the ear and plant traits in diploids and haploids.
Traits Plant Height Height up to the 1 ear  Leaf Length  Leaf Width
  2n n 2n n 2n n 2n n
Ear Length 0.47** 0.17 0.35* 0.13* 0.57** 0.007 0.6** 0.07
Ear Diameter 0.28 0.19 0.020 0.09 0.36*  0.21 0.4* 0.07

*,** The coefficients of correlation are significant at P>0.05 and 0.01 respectively.

In order to provide a general characterization of the correlation between the habitus and earcorn, we calculated the correlation between the indices, combining four traits of the plant and two traits of the earcorn. The indices were calculated in the following way: the value of the trait of an individual plant was divided by the mean value of this trait for all the samples and the data obtained were summed up with those obtained by the same way but for other traits. As a result, each plant in the sampling was characterized by only two figures. One figure characterized the plant traits, the other - the earcorn traits.

We calculated the correlation between the plant index and the earcorn one in the diploid and haploid. The correlation coefficient was 0.53 (significant at P>0.01) at the diploid level, and 0.073 at the haploid one.

This study has shown that the correlation between the earcorn traits and the plant ones differs significantly at the diploid and haploid levels. This difference is true for both individual pairs of the traits and the indices of plant and earcorn traits. The difference was also significant for the earcorn traits in the diploid and haploid plants. The data suggest that the transition to the haploid level leads to a significant change in the correlation between the maize traits. This fact may have a great importance for breeding work. During the selection at the haploid level, the genetically determined expression of the trait can be selected with a high precision in comparison with the selection at the diploid level. Thus, it is possible to reduce the time of selection work and to increase its efficiency.

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