Rozhko I. I. Level of formation and variability of elements of switchgrass (Panicum virgatum L.) seed productivity in the environment of the central Forest-Steppe of Ukraine. – Qualifying scientific work as a manuscript.
A thesis for a Doctor of Philosophy degree by specialty 201 Agronomy (field of study 20 Agrarian and Food Sciences). Poltava State Agrarian Academy of the Ministry of Education and Science of Ukraine, Poltava. – Poltava State Agrarian University of the Ministry of Education and Science of Ukraine, Poltava, 2021.
The thesis presents a solution to an important scientific problem – increasing the yields of switchgrass by studying the best foreign and national variety samples according to economically valuable traits to specify the source material for selection. The peculiarities of the formation of switchgrass seed yields by the elements of yield structure depending on variety assortment, cultivation conditions, and the use of appropriate scientific-based techniques of cultivation are studied.
At the first stage of the research, the variety samples of switchgrass were divided into maturity groups according to the length of the growing season: early maturing (less than 149 days), mid-maturing (150–170 days), and late-maturing (over 170 days). It is found that varieties of switchgrass of all maturity groups are characterized by high or medium lodging resistance and have the highest drought and frost resistance except for Alamo and Kanlow.
According to the degree of influence on the yields of the seeds of switchgrass varieties, the elements of productivity are presented in decreasing order: density of plant stand → the weight of 1000 seeds → plant height. Among the range of switchgrass varieties with high indices of adaptability and yields, Cave-in-Rock and Sunburst are singled out, to a lesser extent, but at a high level – Carthage and Forestburg varieties.
According to the indices of plasticity, stability, and seed yields, the variety samples of switchgrass are conveniently classified into three groups. The first group includes the variety samples Cave-in-Rock, Shelter, Carthage, Forestburg, Blackwell, and Pathfinder as high-yielding ones (307.2–340.5 kg/ha), and they are characterized by low plasticity and high stability. These variety samples can provide high and stable seed yields under soil and climate conditions of the central Forest-Steppe. The second group includes the variety samples of average yield in terms of seed yields (215.4–286.1 kg / ha): Shelter, Sunburst, and Dacotah, which have an average level of genotypic effect expression. The third group is represented by other variety samples: Nebraska, Kanlow and Alamo (seed yields is less than 120.0 kg / ha), characterized by low expression of genotypic effect.
At the second stage of the research of the variety samples Cave-in-Rock (conditional standard), Zoriane, Morozko, and Liniia 1307, it was found that the quantitative indices of the generative part of switchgrass plants contribute significantly to the level of seed yields. The seed yields of the variety samples under study according to the coefficient of determination of trait (d) depend on the number of first-order twigs by 53–59%, on the number of heads by 48–52%, on seed size by 12–21% and on the length and width of the head by 6–12%.
The variety samples Zoriane and Liniia 1307 are discovered, they have the most stable manifestation in terms of the weight index of 1000 seeds. This index had a moderate effect by the correlation coefficient on the seed yields of Zoriane and Liniia 1307. Other variety samples had an average (Morozko) and significant (Cave-in-Rock) coefficient of variation by this index.
It was in studies revealing that the variety samples Zoriane and Liniia 1307 form a high level of yields and conditioned seed efficiency in years which according to the hydrothermal coefficient were characterized as arid and optimal, other varieties provided relatively high seed productivity in years with the hydrothermal coefficient close to 1.
According to the degree of ecological plasticity of the seed yields indices (more than 0.5 t / ha) and seed size (more than 1.5 g), the best compatibility of stability with a high expression of the genotypic effect of these traits was provided by Zoriane and Liniia 1307.
By the indices of vegetative and generative part of plants, the variety samples Zoriane and Liniia 1307 were distinguished, regardless of cultivation conditions.
The variety samples Zoriane and Liniia 1307 are pointed out as those which form heavy seeds, high seed yields (more than 250 kg/ha) of germinated seeds (about 65%) and can be used in further selection work to create and expand the range of switchgrass varieties, which in the long run will enable to obtain high-quality seed material without additional costs, to establish new energy plantations to produce plant biomass for energy purposes and additional products for various industries.
