**3. Conclusions**

Losses in crop yield caused by unfavorable abiotic factors, in particular drought, may reach large dimensions. Drought is usually accompanied by temperature spikes which invoke damage of plants and decrease the yield. Therefore, increasing the drought and heat tolerance are important directions in the modern breeding of cultivated plants.

Along with the traditional methods of selection for tolerance to abiotic stresses at the level of seeds, seedlings, or plants the methods of gametophytic selection, including pollen selection, can be successfully used. It was established that a large part of the genes expressed in the pollen are also exhibits in the plant. This fact indicates that gene transcription occurs in the haploid genome and therefore selection of the traits, which are under the control of genes expressed at both plant and microgametophyte (pollen) levels can be performed effectively.

In our research with sunflowers, when freshly collected pollen of *F*1 plant was heated and used for self-pollination, the drought resistance of the next *F*2 generation was significantly enhanced. This was confirmed by the large number of plants that can survive to bloom in dry field conditions as well as better *F*2 seed germination in osmotic solutions. In another experiment, germination of sunflower pollen in vivo under osmotic stress with polyethylene glycol solution as the selective barrier increased seed germination on the osmotic medium in vitro.

High efficiency of the pollen selection technique for drought tolerance was revealed by us earlier in other crops, such as tomato, maize, castor bean, and linseed. It was in this way that the flax variety was obtained which is a National Standard in Ukraine, and is perfectly adapted to the dry conditions of the south of the country.

Evaluation at the level of pollen may also be of independent interest since the sensitivity to a drought of the plant reproductive system itself is a very important characteristic for many agricultural crops. A possibility to use this approach at the earliest stages of the breeding process, especially when the breeding material is quantitatively limited, is an undeniable advantage of the proposed assessment method.

In general, in the suggested chapter, using as an example different agricultural crop, the effectiveness of pollen selection techniques for drought resistance were demonstrated, as well as methods for assessing plant drought tolerance by its male gametophyte.
