*2.5.1 Effects of high temperature on maize mature pollen grains*

Pollen of maize inbred lines of various origins were collected on sunny days. Then it was placed on glass slides (without medium) in one pollen grain layer. Some slides were placed into a thermostat and heated in the dark at 35°C for 3, 5, 10, and 20 min and other slides were treated for 10, 20, and 30 min at 26°C. After the heat treatment, pollen was inoculated on the nutrient medium. Fresh pollen was used as the control. The percentage of pollen grain germination and pollen tube length were scored. Tolerance of pollen to high temperature was defined by the decrease in viability as compared to the control.

Effects of temperature on the percentage of pollen grain germination in two contrast maize inbreeds (A641 and MK386 lines) are presented in **Table 8**.

Heating mature pollen at 35°C decreased maize mature pollen grain viability even at very short exposures (3–5 min) in MK386 inbred but such treatments did not affect germination percentage in A641 inbred line. Longer treatments (10 min and more) considerably decreased pollen grain germination in A641 and completely inhibited the germination process in the MK386 line. In contrast to the MK386 line, the pollen of A641 inbred endured heating at 35°C for 20 min. Pollen of these accessions also lost its viability at 26°C. After 30 min treatment, MK386 pollen perished completely, while at the same exposure A641 pollen was characterized by the sufficiently large number of germinated pollen grains.

Differences in the tolerance of maize mature pollen to high temperatures were revealed among the inbreeds both at 26°C and 35°C. Even a 5-min treatment at 35°C resulted in decreases in pollen viability that varied in different inbreeds, as compared to the control, from 1.3% in A641 line to 99.1% in MK386 inbred. The effects of high temperatures on pollen tube length were similar. The data obtained allowed us to conclude that the genotypes with high-temperature resistant pollen were characterized

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

