*2.5.3 Changes in monogenic ratios for marker genes in F2 as a result of high-temperature treatment of pollen from F1 hybrids*

A shift in Mendelian segregation ratios is one of the convincing evidence of the genetic activity of gametes. Segregation distortion for any marker gene as a result of treatment of a heterogeneous population of pollen is not yet evidence that this particular gene is expressed in the male gametophyte. A shift in the monogenic ratio for the marker locus can also be due to its linkage with the gene that determines the sensitivity of the gametophyte to the used selection agent. At the same time, conclusions about the localization of this gene (s) on a particular chromosome (chromosomes) of the genome can be drawn.

*F*1 hybrids whose parent components were characterized by differences in heat tolerance at both gametophytic and sporophytic levels were used in our experiments. Mangelsdorf tester was one of the parents of those hybrids. This line is marked with 10 recessive genes, localized in different chromosomes. Seven markers were analyzed, which are typically expressed at the early stages of plant development: *bm2* (chromosome (Chr) l), *lg1* (Chr 2), *a1* (Chr 3), *su1* (Chr 4), *gl1* (Chr 7), *j1* (Chr 8), *g1* (Chr 10).

Mature pollen grains of hybrids and pollen grains at the stage of their maturation were subjected to high-temperature treatment. In the latter case, maize tassels, which were transferred to a laboratory at the beginning of flowering, were exposed to temperature stress. After heat treatment, the pollen was used for self-pollination of the hybrids. In the control pollination was performed with fresh pollen.

With the help of marker analysis, the changes in segregation for seven recessive marker genes were evaluated in comparison with the control. For each *F*2 population at least 400 plants were analyzed. In each case, the percentage of seed germination was quite high and amounted to more than 95%.

Pollen treatments of *F*1 hybrids considerably influenced the monogenic ratio for some marker genes studied in the *F*2 populations. The changes in dominant and recessive genotype ratios were found both after the treatment of mature pollen and pollen during its maturation. Following high-temperature treatment of pollen grains at the maturation stage, differences in the segregation for three markers loci—Gl1, *A*1, and

*Microgametophytic Selection as a Way to Improve Drought Tolerance in Cultivated Plants DOI: http://dx.doi.org/10.5772/intechopen.102735*


## **Table 9.**

*Marker genes for which a shift in monohybrid ratios in F2 was found as a result of temperature treatment of male gametophyte of F1 hybrids of maize.*

Su1 were observed. On the other hand, the treatment of mature pollen of *F*1 hybrids led to a change in monogenic ratios for four marker loci on the first, third, fourth, and tenth chromosomes in comparison with the control (**Table 9**).

Comparing the data on changes in monohybrid ratios in *F*2 as a result of exposure of the microgametophyte to high and low temperatures at the stages of pollen maturation, mature pollen grains and during germination and growth of the pollen tube, one can conclude that the direction of those changes largely depends on the stage of the male gametophyte than on the temperature. The male gametophyte of maize at each stage is characterized by its own set of expressed genes. Some of them, apparently, are expressed at the stages of development and functioning of the microgametophyte.

The presented data on the change in Mendelian segregation in *F*2 under the influence of high temperature on the pollen of *F*1 hybrids indicate the selectivity of this factor and the possibility of efficient selection of genotypes resistant to temperature stress at the microgametophytic level in maize.
