*2.1.2 Pollen heating as a way of selection drought tolerant genotypes*

Treatment of pollen with high-temperature can also be an effective tool for breeders to overcome environmental stresses. Studies on the influence of *F*1 pollen heating on the genetic structure of *F*2 sporophytes showed that this technique can not only change the heat resistance of the segregating populations but its drought resistance as well. To estimate the effectiveness of pollen treatment for drought resistance improvement, comparisons were performed in the dry year 2013 on the number of plants that are able to bloom under such conditions. *F*2 plants obtained from pollination with fresh or heated pollen from *F*1 hybrids were analyzed.

**Table 3** shows that in the year 2013 the amount of rainfall during the two months of vegetation before flowering was only about 60% of the long-term average. Before sowing in April and early May, there was almost no rainfall, while the average daily temperature was significantly higher than the average long-term data. This suggests that for cultivated sunflowers the environmental field conditions during the season of 2013 were arid, at the initial stages of growth and development especially.

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


**Table 3.**

*Weather conditions in Zaporozhye region (Ukraine) before and after sowing of sunflower, 2013.*

*F*1 hybrids were grown in the field conditions during the year 2012 to obtain *F*2 seeds by self-pollination. Before flowering, inflorescences of *F*1 hybrids were isolated. One set of these plants was emasculated within 1–5 days for artificial pollination. The other set was grown without emasculation for collecting fresh pollen. Freshly collected pollen was immediately (in 5–10 min after collection) transferred to the laboratory, placed in parchment packets in a layer of 2–3 mm thick, and heated at the temperature of 60°C using an air bath oven for a period of 1 h and then used to self-pollinate the emasculated *F*1 plants. At the same time, freshly collected pollen without temperature treatment was used to control pollinations. One cm3 of pollen was taken for pollination of each head.

A viability test based on pollen germination on an artificial nutrient medium [25] demonstrates that the heating technique can significantly reduce the percentage of pollen germination on the artificial media. Thus, pollen treatment for 1 h at 60° C reduces the number of germinated pollen grains by almost 4 times, and treatment for 3 h—by more than 20 times, while the germination of pollen drops down to 1%.

Data on the influence of pollen heating in *F*1 hybrids on the adaptability to drought in the *F*2 resulting sporophytic offspring are presented in **Table 4**. As follows from the table, the number of flowering plants was significantly higher in *F*2 populations obtained after 1-h pollen treatment than in the control. These facts indicate that gametophytic selection for heat tolerance increases the adaptability of the *F*2 populations to drought stress [26].

In our earlier studies, we tested the selective effect of different high temperatures on the heterogeneous pollen populations of some interspecific sunflower hybrids [27]. The results showed that pollen heating at 40°C for 3 h did not cause the selective


## **Table 4.**

*Influence of pollen heating in F1 sunflower hybrids on number of flowering plants in F2 population.*


## **Table 5.**

*Influence of pollen heating in F1 hybrids on seed germination of the F2 offspring in an osmotic solution in sunflower.*

elimination of haploid genotypes. Only the use of a higher temperature for pollen treatment led to the shift in the genetic structure of the sporophytic population. As it turned out, pollen heating at the temperature of 60°C for 1 h was already effective.

Tolerance to drought of *F*2 sporophytes after heating pollen of *F*1 hybrids was also assessed by the seed germination in 15% sucrose or 20% PEG solutions. The *F*2 seeds were germinated at the temperature of 25°C for a period of 4 days (sucrose) and 3 days (PEG 6000). After that, the percentage of seed germination was calculated **(Table 5).**

As can be seen from **Table 5**, the heating of *F*1 pollen increased the drought resistance of *F*2 sporophytic population estimated by seed germination in a 15% sucrose solution or in 20% PEG 6000 solution. Germination in the osmotic of *F*2 seeds that were developed after pollen heating was more than 3–6 times higher compared with the *F*2 seeds resulting from the pollination of *F*1 hybrids with fresh pollen.

These facts reveal that gametophytic selection for heat tolerance increases both the adaptability to the drought of the *F*2 populations in dry field conditions and the germination of *F*2 seeds in the conditions of osmotic stress. Thus, during the pollen heating, we observe the indirect selection that increases drought resistance of sporophytic offspring. It can be reasonably assumed that the genes which define sunflower drought resistance are linked to the genes determining heat resistance.
