Usage of introduced species in forest plantations can increase the productivity of woodlands as well as improve their landscape, decorative properties and enrich the plant resources of the country.
The aim of the study was to determine the quality of pollen (its viability, abnormal deviation in pollen grains and length of pollen tubes) of various introduced pines species in conditions of State Enterprise “Kyiv Forest Research Station”.
Materials and Methods
The pinetum with an area of 2.0 ha was established with seedlings and grafted seedlings grown in containers and includes 20 species of pine trees.
To determine the viability of pollen of different pine species, we used the germination method on 1% agar-agar with a 10% sucrose solution in a sagging drop in Petri dishes at a temperature of 26–30°C for 3 days. At the end of the germination, Petri dishes with sprout pollen were placed into a freezer for 2–4 hours and then stored in a refrigerator.
Pollen specimens were examined microscopically with an ocular micrometer with 16 × 8 magnification. About 500 pollen grains were counted in some fields. For them, we determined several indicators, namely the number of normally developed and underdeveloped pollen grains, the number of pollen grains with 3–4 utricles and the number of sprouted pollen grains, including those with abnormal pollen tubes.
In some pine species, massive pollination began with a two-week difference and lasted 6 days on an average. In all types of pine, ‘flowering’ of megastrobiles and flying the pollen out of the microstrobiles coincide, which makes it possible to pollinate. The pollen vitality of most pine species is higher than 90%. In growth-supporting microenvironment, the pollen germinates evenly: the length of pollen tubes reaches 100–175 μm and this feature’s variability is very low: 3.2–6.1%. It points to the relative stability of the growth intensity of pollen tubes. Deviation from the norm in the form of two pollen tubes was found in almost all types of pines. The total number of anomalous pollen grains is insignificant (0–3.8%) and does not significantly affect pollen viability.
Only 8 of 18 pine species which had ‘bloomed’, formed the cones by free pollination. Moreover, not all the cones had full seeds. Introduced species showed a low yield of seeds from free pollination – 0.05…0.79%, apart from ponderosa pine which had 2.22%. In the conditions of Kyiv Forest Research Station seed embryos of most introduced pine trees died immediately after pollination, resulting in a small number of full grain seeds, and the rest were wings with barely noticeable pyknotic structures.
The seed germination of introduced pines differed a lot. Thus, this indicator for ponderosa pine was 0.5%, whereas Japanese black pine and Austrian pine had high seed germination: 60–65%.
There was a probable positive correlation of average strength between the pollen viability of introduced pine species and the growth intensity of pollen tubes (r = 0.566, t0.05 = 2.75 at n = 18). The seed number in cones of different pine species is not related to the quality of their pollen. The improbability of impact may be due to a small number of pairs: the seeds were harvested from only 8 species. At the same time, this may indicate a deviation in the development of megastrobiles and point at the fact that the quality of pollen is not limiting in the development of the generative sphere of pine trees.
There is a high negative correlation between the seed number in a cone and soil germination of the seeds (r = -0.725); it is 5% probable. In general, in the State Enterprise “Kyiv Forest Research Station” pinetum, introduced trees successfully ‘bloom’ but do not form a sufficient quantity of full-fledged seeds.
The pollen vitality of most pine species is higher than 90%, and it isn’t significantly affected by a small number of abnormal pollen grains (0–3.8%). Deviation in the form of two pollen tubes in almost all types of pines (up to 37.8%) was detected during the pollen germination. There is a positive correlation with a 5% probability value (r = 0,556) between the pollen viability and the length of the pollen tubes.
Only 8 of 18 pine species which had ‘bloomed’, formed the cones by free pollination. At that, not all the cones had full seeds. Introduced species showed a low seed yield from free pollination – 0.05…0.79%. Japanese black pine was an exception – it showed a 2.22% seed yield. In the conditions of Kyiv Forest Research Station seed embryos of most introduced pine trees died immediately after pollination, resulting in a small number of full grain seeds. The rest of them formed wings with barely noticeable pyknotic structures.
There is a strong negative correlation with a 1% probability value between the seeds number in a cone and the soil germination of the seeds (r = - 0,725). It indicates a significant proportion of normally developed empty seed whose embryos died.
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