**Table 8.**

*Effects of mature pollen heating on pollen grain germination percentage in two maize accessions with contrasting heat resistance.*

not only by higher germination percentage, but also a better ability to develop normal pollen tubes at high temperatures.

The mechanism which induces the rapid loss of viability of tricellulate cereal pollen is not yet clear. A reduction up to 80% of the original water content of maize pollen did not essentially affect its viability. With water loss greater than this value, pollen grains undergo irreversible changes.

A comparison of the heat resistance of pollen of inbred lines with their heat resistance at the stage of 20-day-old seedlings suggests a certain pattern. Lines with pollen more resistant to high temperature are also characterized by more resistant to this stress sporophyte. The correlation coefficient between the temperature resistance of the male gametophyte and the sporophyte turned out to be rather high and varied in different years from 0.6 to 0.78.

The positive relationship between the resistance to high temperatures of the gametophyte and sporophyte suggests that this trait is controlled by the same genetic system at both the haploid and diploid levels. In this case, the assessment of the sporophyte quality can be made based on the analysis of pollen traits.

Genotypic differences in the response of pollen to temperature stress give rise to the hope that the selection of mature pollen grains in a heterogeneous population will be successful in increasing the resistance of the sporophytic generation to high temperatures. In maize, mature pollen can be not only a tool for increasing sporophyte resistance. Mature pollen can be a breeding goal, given that the resistance of pollen grains to high temperatures after they are shed from the anthers is no less important for ensuring high crop yields than the resistance of a vegetative plant.
