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

As a result of this experimental study, it was found that 6 and 12 h of heat treatment of pollen completely deprived it of the ability to germinate. Fruits were not set during pollination with such pollen, which indicated the loss of not only vitality but fertilizing ability as well. As optimal for gametophytic selection a 3 h treatment was accepted, which reduced the viability of pollen from 20–30% to 2–5%. The sum of temperatures under this effect amounted to 174°C and was close to the sum of lethal temperatures found for tomato varieties with high heat resistance of pollen.

Subsequently, the pollen of interspecific hybrids after 1 and 3 h of heating was used for pollination and raising *F*2 and BC1 offspring. It should be noted that the Mo 500 inbred line is a multimarket mutant, which is marked with 4 genes located in the 2nd and 6th chromosomes. These genes are easily identified in the early stages of plant development.

Marker analysis of *F*2 and BC1 segregating plant populations revealed differences after pollen treatment. Deviations from the control were insignificant for genes marking the second chromosome but significant for gene "*c*" (potato leaf), localized on the 6th chromosome (**Table 7**).

Only a 3 h treatment of *F*1 hybrid pollen with high temperature led to a deviation of monogenic ratios in the direction of increasing the number of alleles of wild species. A decrease in the number of recessives at the *C* locus, emerged as a result of a 3 h temperature treatment of the hybrid pollen indicates that selection for heat resistance was accompanied by a predominant elimination of pollen grains of mutant type as compared to wild ones, such as *L. minutum* and *S. pennellii*.

In general, of the 4 studied loci, only the *C* locus has proved to be "temperature-sensitive" at the stage of mature pollen. Later, marker loci of the 4th and 11th chromosomes were involved in research. However, analysis of *F*2 and BC1 plants after heating of *F*1 hybrid pollen did not reveal significant differences from the


## **Table 7.**

*Influence of pollen heating of F1 tomato hybrids on the segregation ratio in F2 or BC1 generations for "potato leaf" marker-trait.*

control in the allele frequencies of wild tomato species for the marker genes from those chromosomes.

It can be assumed that the 6th chromosome of a tomato or its section within the immediate vicinity of the *C* locus determines to some extent the sensitivity of mature pollen to high temperatures. It is important to note that the same locus was also "perceptive" to low temperatures as it fluctuated in segregations in accordance with pollen germination ability and pollen tube growth at cold stress.

To reveal the differences between the segregating populations of sporophytes obtained after pollination with fresh and heated pollen, those populations were tested against the high-temperature background at the stage of seedlings and 4–6 leaves. It was determined that in both cases the experimental populations exceeded the control ones in terms of heat resistance. That is, pollen selection for high-temperature resistance is effective and can be used as a helpful tool in breeding programs.
